(Manual) auto cad 2000 visual lisp tutorial (autocad)

VISUAL LISP™ TUTORIAL
00120-010000-5080 January 29, 1999

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iii
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Garden Path Revisited: Working in Visual LISP . . . . . . . . . . . . . . . . . . 2
Tutorial Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Lesson 1 Designing and Beginning the Program . . . . . . . . . . . . . . . . . . . . . . 5
Defining Overall Program Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Getting Started with Visual LISP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Looking at Visual LISP Code Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Analyzing the Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Filling the Gaps in the Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Letting Visual LISP Check Your Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Running the Program with Visual LISP . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Wrapping Up Lesson 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Lesson 2 Using Visual LISP Debugging Tools . . . . . . . . . . . . . . . . . . . . . . . . 13
Differentiating between Local and Global Variables . . . . . . . . . . . . . . . . . 14
Using Local Variables in the Program . . . . . . . . . . . . . . . . . . . . . . . . 15
Examining the gp:getPointInput Function . . . . . . . . . . . . . . . . . . . . 16
Using Association Lists to Bundle Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Putting Association Lists to Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Storing the Return Value of gp:getPointInput in a Variable . . . . . . . 19
Examining Program Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Revising the Program Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Commenting Program Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Setting a Breakpoint and Using More Watches . . . . . . . . . . . . . . . . . . . . . 24
Using the Debug Toolbar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Stepping through Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

iv | Contents
Watching Variables As You Step through a Program . . . . . . . . . . . . 29
Stepping Out of the gp:getPointInput Function and into C:Gpmain. . .30
Lesson 3 Drawing the Path Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Planning Reusable Utility Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Converting Degrees to Radians. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Converting 3D Points to 2D Points . . . . . . . . . . . . . . . . . . . . . . . . . 35
Drawing AutoCAD Entities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Creating Entities Using ActiveX Functions. . . . . . . . . . . . . . . . . . . . 37
Using entmake to Build Entities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Using the AutoCAD Command Line . . . . . . . . . . . . . . . . . . . . . . . . 37
Enabling the Boundary Outline Drawing Function. . . . . . . . . . . . . . . . . . 38
Passing Parameters to Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Working with an Association List. . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Using Angles and Setting Up Points . . . . . . . . . . . . . . . . . . . . . . . . . 40
Understanding the ActiveX Code in gp:drawOutline . . . . . . . . . . . 42
Ensuring That ActiveX Is Loaded . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Obtaining a Pointer to Model Space . . . . . . . . . . . . . . . . . . . . . . . . . 43
Constructing an Array of Polyline Points . . . . . . . . . . . . . . . . . . . . . 44
Constructing a Variant from a List of Points . . . . . . . . . . . . . . . . . . 45
Putting It All Together. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Lesson 4 Creating a Project and Adding the Interface . . . . . . . . . . . . . . . . . 51
Modularizing Your Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Using Visual LISP Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Adding the Dialog Box Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Defining the Dialog Box with DCL. . . . . . . . . . . . . . . . . . . . . . . . . . 55
Saving a DCL File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Previewing a Dialog Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Interacting with the Dialog Box from AutoLISP Code. . . . . . . . . . . . . . . . 59
Setting Up Dialog Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Loading the Dialog File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Loading a Specific Dialog into Memory . . . . . . . . . . . . . . . . . . . . . . 60
Initializing the Default Dialog Values. . . . . . . . . . . . . . . . . . . . . . . . 61
Assigning Actions to Tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Starting the Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Unloading the Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Determining What to Do Next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Putting the Code Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Updating a Stubbed-Out Function . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Providing a Choice of Boundary Line Type . . . . . . . . . . . . . . . . . . . . . . . . 66

Contents | v
Cleaning Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Running the Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Lesson 5 Drawing the Tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Introducing More Visual LISP Editing Tools. . . . . . . . . . . . . . . . . . . . . . . . 70
Matching Parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Completing a Word Automatically . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Completing a Word by Apropos . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Getting Help with a Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Adding Tiles to the Garden Path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Applying Some Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Applying Some Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Drawing the Rows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Drawing the Tiles in a Row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Looking at the Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Testing the Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Lesson 6 Acting with Reactors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Reactor Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Reactor Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Designing Reactors for the Garden Path. . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Selecting Reactor Events for the Garden Path . . . . . . . . . . . . . . . . . . 85
Planning the Callback Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Planning for Multiple Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Attaching the Reactors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Storing Data with a Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Updating the C:GPath Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Adding Reactor Callback Functions. . . . . . . . . . . . . . . . . . . . . . . . . . 91
Cleaning Up After Your Reactors. . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Test Driving Your Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Examining Reactor Behavior in Detail. . . . . . . . . . . . . . . . . . . . . . . . 93
Lesson 7 Putting It All Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Planning the Overall Reactor Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Reacting to More User-Invoked Commands . . . . . . . . . . . . . . . . . . . 97
Storing Information within the Reactor Objects. . . . . . . . . . . . . . . . 99
Adding the New Reactor Functionality. . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Adding Activity to the Object Reactor Callback Functions. . . . . . . 103
Designing the gp:command-ended Callback Function. . . . . . . . . . 104

vi | Contents
Handling Multiple Entity Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Using ActiveX Methods in Reactor Callback Functions. . . . . . . . . 105
Handling Nonlinear Reactor Sequences . . . . . . . . . . . . . . . . . . . . . 105
Coding the command-ended Function . . . . . . . . . . . . . . . . . . . . . 107
Updating gp:Calculate-and-Draw-Tiles. . . . . . . . . . . . . . . . . . . . . . 110
Modifying Other Calls to gp:Calculate-and-Draw-Tiles . . . . . . . . . 112
Redefining the Polyline Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Looking at the Functions in gppoly.lsp . . . . . . . . . . . . . . . . . . . . . . 114
Understanding the gp:RedefinePolyBorder Function. . . . . . . . . . . 115
Understanding the gp:FindMovedPoint Function . . . . . . . . . . . . . 116
Understanding the gp:FindPointInList Function . . . . . . . . . . . . . . 116
Understanding the gp:recalcPolyCorners Function . . . . . . . . . . . . 118
Understanding the gp:pointEqual, gp:rtos2, and
gp:zeroSmallNum Functions . . . . . . . . . . . . . . . . . . . 118
Wrapping Up the Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Building an Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Starting the Make Application Wizard . . . . . . . . . . . . . . . . . . . . . . 120
Wrapping Up the Tutorial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
LISP and AutoLISP Books . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
AutoLISP Books . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
General LISP Books . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

In This Chapter
1
Introduction
This tutorial is designed to demonstrate several
powerful capabilities of the Visual LISP™
programming
environment for AutoCAD®
and introduce features of
the AutoLISP®
language that may be new to you.
The purpose of the tutorial is to draw a garden path
using an automated drawing tool that minimizes
drafting time and shows the power of parametric
programming. You will learn how to create a drawing
routine that automates the generation of a complex
shape—the kind of drafting operation you do not want
to draw over and over again, if it means starting from
scratch each time.
s The Garden Path Revisited:
Working in Visual LISP
s Tutorial Overview

2 | I Introduction
The Garden Path Revisited: Working in Visual
LISP
This tutorial is intended for experienced AutoCAD users and assumes you
have some familiarity with either LISP or AutoLISP. It also assumes you
understand basic Windows®
file management tasks such as creating direc-
tories, copying files, and navigating through the file system on your hard
disk or network.
If you are familiar with AutoLISPand have used earlier versions of the Garden
Path tutorial, you will notice several differences:
s The Visual LISP (VLISP™
) environment is introduced. This environment
provides you with editing, debugging, and other tools specific to the cre-
ation of AutoLISP applications. Previous versions of the Garden Path
tutorial taught AutoLISP language concepts—not VLISP development
tools.
s New ActiveX™
and Reactor functions of AutoLISP are demonstrated, as
well as several other extensions to the AutoLISP language provided with
VLISP.
s The tutorial has been thoroughly redesigned. Even if you are familiar with
the previous version, you will encounter entirely different source code
and a much more extensive tutorial.
s There are two possible execution contexts for the Garden Path tutorial.
The application may be run as interpreted LISP in piecemeal files and/or
functions that are loaded into a single document. Alternately, the program
code can be compiled into a VLX application, denoted by a *.vlx execut-
able. A VLX operates from a self-contained namespace that can interact
with the application-loading document.

Tutorial Overview | 3
Tutorial Overview
Your goal in this tutorial is to develop a new command for AutoCAD that
draws a garden path and fills it with circular tiles. The tutorial is divided into
seven lessons. As you progress from lesson to lesson, you receive progres-
sively less detailed instructions on how to perform individual tasks. Help is
available in the VLISP documentation if you have any questions.
Lessons 4 and 5 are at an intermediate level and go beyond basic AutoLISP
concepts. Lessons 6 and 7 contain advanced and fairly complex program-
ming tasks and are designed for experienced AutoLISP developers.
All the source code for drawing the garden path at each stage of development
is available on the AutoCAD installation CD, but the tutorial files are only
included in your installation if you chose Full install, or if you chose Custom
install and selected the Samples item. If you previously installed AutoCAD
and did not install the samples, rerun the install, choose Custom, and select
only the Samples item.
The directory structure for the source code files follows the tutorial lesson
plan:
<AutoCAD directory>TutorialVisualLISPLesson1
<AutoCAD directory>TutorialVisualLISPLesson2
and so on.
It is recommended you do not modify the sample source code files supplied
with AutoCAD. If something is not working correctly within your program,
you may want to copy the supplied source code into your working directory.
Throughout the tutorial, the working directory is referred to as:
<AutoCAD directory>TutorialVisualLISPMyPath
If you choose a different path for your working directory, substitute your
directory name at the appropriate times.
Finally, read the Getting Started section of the Visual LISP Developer’s Guide.
It has a brief introduction to many concepts you need to complete this
tutorial.

5
In This Lesson
1
Designing and Beginning
the Program
In this first lesson, you'll begin by defining what the
application will do. Using the Visual LISP (VLISP) devel-
opment environment, you'll create a LISP file and begin
writing AutoLISP code to support your application.
In the process, you'll begin to discover how VLISP
facilitates application development.
s Defining Overall Program Goals
s Getting Started with Visual LISP
s Looking at Visual LISP Code
Formatting
s Analyzing the Code
s Filling the Gaps in the Program
s Letting Visual LISP Check Your
Code
s Running the Program with Visual
LISP
s Wrapping Up Lesson 1

6 | Lesson 1 Designing and Beginning the Program
Defining Overall Program Goals
Developing an AutoLISP program begins with an idea for automating some
aspect of AutoCAD. It may be a need to speed up a repetitive drafting func-
tion, or to simplify a complex series of operations. For the tutorial, the
garden path you want your program to draw is a complex shape with a vari-
able number of components, based on initial input from the user. Here’s
what it will look like:
Your program must do the following to draw the garden path:
s Given a start point, an endpoint, and a width, draw a rectilinear bound-
ary. The boundary can be at any 2D orientation. There should be no limit
on how large or small it can be.
s Prompt the user for tile size and tile spacing values. The tiles are simple
circles and will fill the boundary but must not overlap or cross the
boundary.
s Place the tiles in alternating rows.
To see how things should work, you can run a completed version of the appli-
cation that is supplied with AutoCAD.

Getting Started with Visual LISP | 7
To run the supplied example
1 From the AutoCAD Tools menu, choose Load Application.
2 Select gardenpath.vlx from the TutorialVisualLISP directory, and choose Load.
3 Press Close.
4 At the Command prompt, enter gpath.
5 Respond to the first two prompts by picking a start point and an endpoint in
the AutoCAD graphics window.
6 Enter 2 at the Half Width of Path prompt.
7 Choose OK when prompted by the Garden Path Tile Specifications dialog
box.
Getting Started with Visual LISP
Now that you’ve seen how the application is supposed to work, you can
begin developing it with VLISP. But first, it helps to demonstrate what can
happen when VLISP is waiting for control to return from AutoCAD. You may
have already encountered this.
To see Visual LISP wait for control to return from AutoCAD
1 At the AutoCAD Command prompt, enter vlisp to start Visual LISP.
2 Switch back to the AutoCAD window (either select AutoCAD from the task-
bar or press ALT+TAB and choose AutoCAD), and enter gpath at the AutoCAD
Command prompt.
3 Before responding to the prompts from gpath, switch back to the VLISP
window.
In the VLISP window, the mouse pointer appears as a VLISP symbol and you
cannot choose any commands or enter text anywhere in the VLISP window.
The pointer symbol is a reminder that there is an activity you must complete
in AutoCAD before resuming work with VLISP. Remember this whenever you
see the VLISP pointer.
4 Return to the AutoCAD window and respond to all the prompts from gpath.
Now you are ready to begin building the garden path application.

To begin application development with Visual LISP
1 From the VLISP File menu, choose New File.
2 Enter the following code in the text editor window (it is the window titled
“<Untitled-0>”); you can omit the comments, if you wish:
;;; Function C:GPath is the main program function and defines the
;;; AutoCAD GPATH command.
(defun C:GPath ()
;; Ask the user for input: first for path location and
;; direction, then for path parameters. Continue only if you have
;; valid input.
(if (gp:getPointInput) ;
(if (gp:getDialogInput)
(progn
;; At this point, you have valid input from the user.
;; Draw the outline, storing the resulting polyline
;; "pointer" in the variable called PolylineName.
(setq PolylineName (gp:drawOutline))
(princ "nThe gp:drawOutline function returned <")
(princ PolylineName)
(princ ">")
(Alert "Congratulations - your program is complete!")
)
(princ "nFunction cancelled.")
)
(princ "nIncomplete information to draw a boundary.")
)
(princ) ; exit quietly
)
;;; Display a message to let the user know the command name.
(princ "nType gpath to draw a garden path.")
(princ)
3 Choose File ® Save As from the menu, and save the code in the new file as
<AutoCAD directory>TutorialVisualLISPMyPathgpmain.lsp.
4 Review your work.
Looking at Visual LISP Code Formatting
VLISP recognizes the various types of characters and words that make up an
AutoLISP program file and highlights the characters in different colors. This
makes it easier for you to spot something incorrect quickly. For example, if
you miss a closing quotation mark following a text string, everything you
type continues to display in magenta, the color denoting strings. When you
enter the closing quotation mark, VLISP correctly colors the text following
the string, according to the language element it represents.

Analyzing the Code | 9
As you enter text, VLISP also formats it by adding spacing and indentation.
To get VLISP to format code you copy into its text editor from another file,
choose Tools ® Format Code in Editor from the VLISP menu.
Analyzing the Code
The defun function statement defines the new function. Notice the main
function is named C:GPath. The C: prefix establishes that this function is
callable from the AutoCAD Command line. GPath is the name users enter to
launch the application from the AutoCAD Command prompt. The functions
that obtain input from users are named gp:getPointInput and
gp:getDialogInput. The function that draws the garden path outline is
gp:drawOutline. These names are prefixed with gp: to indicate they are
specific to the garden path application. This is not a requirement, but it is a
good naming convention to use to distinguish application-specific functions
from general utility functions you frequently use.
In the main function, princ expressions display the results of the program if
it runs successfully, or a warning message if the program encounters an
unexpected event. For example, as will be seen in Lesson 2, if the user presses
ENTER instead of picking a point on the screen, the call to gp:getPointInput
ends prematurely, returning a nil value to the main function. This causes the
program to issue a princ message of “Incomplete information to draw a
boundary.”
The call to princ near the end of the program serves as a prompt. Upon appli-
cation load, the prompt informs users what they need to type to initiate the
drawing of a garden path. The final princ without a string argument forces
the program to exit quietly, meaning the value of the main function’s final
expression is not returned. If the final suppressing princ were omitted, the
prompt would display twice.
Filling the Gaps in the Program
For the code in this new file to work correctly, you must write three more
function definitions. The main garden path code contains calls to three cus-
tom functions:
s gp:getPointInput
s gp:getUserInput
s gp:drawOutline

For now, you will just write stubbed-out function definitions. A stubbed-out
function serves as a placeholder for the complete function that is to follow.
It allows you to try out pieces of your code before adding all the detail needed
to complete the application.
To define stubbed-out functions for the application
1 Position your cursor at the top of the program code in the text editor window
and press ENTER a couple of times to add blank lines.
2 Enter the following code, beginning where you inserted the blank lines:
;;; Function gp:getPointInput will get path location and size
(defun gp:getPointInput()
(alert
"Function gp:getPointInput will get user drawing input"
)
;; For now, return T, as if the function worked correctly.
T
)
;;; Function gp:getDialogInput will get path parameters
(defun gp:getDialogInput ()
(alert
"Function gp:getDialogInput will get user choices via a dialog"
)
;;For now, return T, as if the function worked correctly.
T
)
;;; Function gp:drawOutline will draw the path boundary
(defun gp:drawOutline ()
(alert
(strcat "This function will draw the outline of the polyline"
"nand return a polyline entity name/pointer."
)
)
;; For now, simply return a quoted symbol. Eventually, this
;; function will return an entity name or pointer.
'SomeEname
)
Right before the end of each input function is a line of code that contains
only a T. This is used as a return value to the calling function. All AutoLISP
functions return a value to the function that called them. The letter T is the
symbol for “true” in AutoLISP, and adding it causes the function to return a
true value. The way gpmain.lsp is structured, each input function it calls must
return a value other than nil (which indicates “no value”) for the program
to proceed to the next step.
An AutoLISP function will, by default, return the value of the last expression
evaluated within it. In the stubbed-out functions, the only expression is a call
to the alert function. But alert always returns nil. If this is left as the last

Letting Visual LISP Check Your Code | 11
expression in gp:getPointInput, it will always return nil, and you will never
pass through the if to the gp:getDialogInput function.
For a similar reason, the end of the gp:DrawOutline function returns a
quoted symbol ('SomeEname) as a placeholder. A quoted symbol is a LISP con-
struct that is not evaluated. (If you are curious about how the LISP language
works, there are a number of good books available, mentioned at the end of
this tutorial.)
Letting Visual LISP Check Your Code
VLISP has a powerful feature for checking your code for syntactical errors.
Use this tool before trying to run the program. You can catch common typing
errors such as missing parentheses or missing quotation marks, and other
syntactical problems.
To check the syntax of your code
1 Make sure the text editor window containing gpmain.lsp is the active win-
dow. (Click in the title bar of the window to activate it.)
2 From the VLISP menu, choose Tools ® Check Text in Editor.
3 The Build Output window appears with the results of the syntax check. If
VLISP did not detect any errors, the window contains text similar to the
following:
[CHECKING TEXT GPMAIN.LSP loading...]
......
; Check done.
If you have problems and need help, refer to the “Developing Programs with
Visual LISP” chapter of the Visual LISP Developer’s Guide. See if you can deter-
mine where the problem is located. If you are spending too much time
locating the problem, use the sample gpmain.lsp file provided in the lesson1
directory to continue with the tutorial.
To use the supplied gpmain.lsp program (if necessary)
1 Close the text editor window containing the gpmain.lsp code you entered.
2 Choose File ® Open File from the VLISP menu, and open the gpmain.lsp file
in the TutorialVisualLISPlesson1 directory.
3 Choose File ® Save As and save the file in your TutorialVisualLISPMyPath
directory as gpmain.lsp, replacing the copy you created.

Running the Program with Visual LISP
Running AutoLISP programs in VLISP allows you to use the many debugging
features of VLISP to investigate problems that may occur in your application.
To load and run the program
1 With the text editor window active, choose Tools ® Load Text in Editor from
the VLISP menu.
2 At the _$ prompt in the VLISP Console window, enter (C:GPath).
The Console window expects commands to be entered in AutoLISP syntax,
so all function names must be enclosed in parentheses.
3 Press ENTER or click OK in response to the message windows. The final mes-
sage should read “Congratulations – your program is complete!”
NOTE If AutoCAD is minimized when you run gpath, you will not see the
prompts until you restore the AutoCAD window (using either the taskbar or
ALT+TAB).
Wrapping Up Lesson 1
In this lesson, you
s Defined program goals.
s Learned the value of stub functions.
s Learned about naming functions to identify them as specific to your appli-
cation or as general functions to be used over and over.
s Learned how to use VLISP to check your code.
s Learned how to load and run a program in VLISP.
You are done with this lesson. Save your program file again to be certain you
have the latest revisions.

13
In This Lesson
2
Using Visual LISP
Debugging Tools
This lesson teaches you how to use several valuable
VLISP debugging tools that speed up the development
of AutoLISP programs. You will also learn the difference
between local and global variables, and when to use
them. Your program will become more active—prompt-
ing users to enter some information. The information
will be stored in a list and you’ll begin to understand
the power of using lists within your AutoLISP programs.
After all, LISP got its name because it is a LISt Processing
language.
s Differentiating between Local
and Global Variables
s Using Association Lists to
Bundle Data
s Examining Program Variables
s Revising the Program Code
s Commenting Program Code
s Setting a Breakpoint and Using
More Watches

14 | Lesson 2 Using Visual LISP Debugging Tools
Differentiating between Local and Global
Variables
This lesson discusses the use of local variables versus global document
variables. Global variables are accessible by all functions loaded within a doc-
ument (an AutoCAD drawing). These variables may retain their value after
the program that defined them completes. Sometimes, this is what you want.
You’ll see an example of this later in the tutorial.
Local variables retain their value only as long as the function that defined
them is running. After the function finishes running, the local variable val-
ues are automatically discarded, and the system reclaims the memory space
the variable used. This is known as automatic garbage collection, and is a fea-
ture of most LISP development environments, such as VLISP. Local variables
use memory more efficiently than global variables.
Another big advantage is that local variables make it easier to debug and
maintain your applications. With global variables, you are never sure when
or in which function the variable’s value might be modified; with local vari-
ables you don’t have as far to trace. You usually end up with fewer side effects
(that is, one part of the program affecting a variable from another part of the
program).
Because of the advantages cited, this tutorial uses local variables almost
exclusively.
FunA
(setq localvara "boo")
(setq localvara "hoo")
(setq globalvara "foo")
(funB)
(print localvara)
"boo"
(print globalvara)
"whenever"
FunB
(print localvara)
nil
(print localvarb)
nil
(print globalvara)
"foo"
(setq globalvara "whatever)
(setq localvara "fie")
(funC) FunC
(print localvara)
nil
(print globalvara)
"whatever"
(setq globalvara)
"whenever"

Differentiating between Local and Global Variables | 15
NOTE If you have been working with AutoLISP for some time, you may have
developed the practice of using global variables during development to examine
your program while you are building it. This practice is no longer necessary, given
the powerful debugging tools of VLISP.
Using Local Variables in the Program
Refer to the gp:getPointInput function you created in Lesson 1:
(defun gp:getPointInput()
(alert
"Function gp:getPointInput will get user drawing input"
)
;; For now, return T, as if the function worked correctly.
T
)
So far, the function does not do much work. You will now begin to build on
it by adding functions to get input from the user, which will define the start
point, endpoint, and width of the path.
It is a good practice when creating AutoLISP programs to emulate the behav-
ior of AutoCAD. For this reason, instead of asking the user to indicate the
width by selecting a point in the drawing in respect to the centerline of a lin-
ear shape, your program should ask for a selection of the half width.
Once the gp:getPointInput function is complete, the variables, as well as
the values assigned to them, will no longer exist. Therefore, you will store
user-supplied values in local variables. Here’s what the function might look
like:
(defun gp:getPointInput(/ StartPt EndPt HalfWidth)
(if (setq StartPt (getpoint "nStart point of path: "))
(if (setq EndPt (getpoint StartPt "nEndpoint of path: "))
(if (setq HalfWidth (getdist EndPt "nHalf width of path: "))
T
)
)
)
)
The local variables are declared following the slash character, in the defun
statement that begins the function. The first call to getpoint prompts the
user to indicate a start point. The endpoint is then acquired in relation to the
chosen start point. While selecting the endpoint, the user will observe a
rubber-band line extending from the start point. Similarly, while setting the
half width value, the user will view another rubber-band line, this time rep-
resenting distance, emanating from the endpoint.

To see how gp:getPointInput works
1 Type the gp:getPointInput code into the VLISP Console window.
2 With the Console window cursor following the last parenthesis of the block
of code (or on the next line below it), press ENTER and you will replace any
previously loaded version of the gp:getPointInput function.
3 Execute the function from the Console window by entering
(gp:getPointInput) at the Console prompt.
4 Pick points when prompted, and enter a half width value.
Examining the gp:getPointInput Function
When you ran the gp:getPointInput function, control was automatically
passed from VLISP to AutoCAD. You responded to three prompts, after which
control was passed back from AutoCAD to VLISP, and a T symbol displayed
in the Console window.
Within the program, here’s what happens:
1 VLISP waits for you to pick the first point.
2 When you pick the first point, the program stores the value of your selection
(a list containing three coordinate values—an X, Y, and Z value) into the
StartPt variable.
3 The first if function examines the result to determine whether a valid value
was entered or no value was entered. When you pick a start point, control is
passed to the next getpoint function.
4 When you pick an endpoint, the point value is stored in the Endpt variable.
5 The result of this statement is examined by the next if statement, and con-
trol is passed to the getdist function.
6 The getdist function acts in a similar fashion when you pick a point on the
screen or enter a numeric value. The result of the getdist function is stored
in the HalfWidth variable.
7 Program flow reaches the T nested deeply within the function. No other
functions follow this, so the function ends, and the value T is returned. This
is the T you see at the Console window.
You need some way to return values from one function to another. One way
to do this is to create a list of the values retrieved from gp:getPointInput, as
highlighted in the following code:

Using Association Lists to Bundle Data | 17
(defun gp:getPointInput ( / StartPt EndPt HalfWidth )
(list StartPt EndPt HalfWidth)
)
)
)
)
Copy this version of gp:getPointInput into the Console window and press
ENTER. Here’s an opportunity to try another feature of the Console window.
To use the Console window history feature to run gp:getPointInput
1 Press TAB. This invokes the Console history command, cycling through any
commands previously entered in the Console window. If you go too far, press
SHIFT +TAB to cycle in the other direction.
2 When you see (gp:getPointInput) at the Console prompt, press ENTER to
execute the function once again.
3 Respond to the prompts as before.
The function returns a list containing two nested lists and a real (floating
point) value. The return values look like the following:
((4.46207 4.62318 0.0) (7.66688 4.62318 0.0) 0.509124)
These values correspond to the StartPt, EndPt, and HalfWidth variables.
Using Association Lists to Bundle Data
The previous example works, but you can do better. In the next exercise, you
will build an association list, or assoc list (after the LISP function that deals
with association lists). In an association list, the values you are interested in
are associated with key values. Here is a sample association list:
((10 4.46207 4.62318 0.0) (11 7.66688 4.62318 0.0) (40 . 1.018248))
In the sample association list, the key values are the numbers 10, 11, and 40.
These key values serve as a unique index within the list. This is the mecha-
nism AutoCAD uses to return entity data to AutoLISP if you access an entity
from within your program. A key value of 10 indicates a start point, a key
value of 11 is typically an endpoint.

What are the advantages of an association list? For one thing, unlike the reg-
ular list, the order of the values returned does not matter. Look at the first list
again:
((4.46207 4.62318 0.0) (7.66688 4.62318 0.0) 0.509124)
Look at the return values; it is not apparent which sublist is the start point
and which is the endpoint. Furthermore, if you modify the function in the
future, any other function that relies on data returned in a specific order may
be adversely affected.
Using an association list, the order of the values does not matter. If the order
of an association list changes, you can still tell which value defines what. For
example, an 11 value is still an endpoint, regardless of where it occurs within
the overall list:
((11 7.66688 4.62318 0.0) ; order of list
(40 . 1.018248) ; has been
(10 4.46207 4.62318 0.0)) ; modified
Putting Association Lists to Use
When you use association lists, you should document what your key values
represent. For the garden path, the key values of 10, 11, 40, 41, and 50 will
mean the following:
s 10 indicates the 3D coordinate of the start point of the path.
s 11 indicates the 3D coordinate of the endpoint of the path.
s 40 indicates the width (not the half width) of the path.
s 41 indicates the length of the path, from start to end.
s 50 indicates the primary vector (or angle) of the path.
The following is an updated version of the gp:getPointInput function.
Within it, an AutoLISP function called cons (short for construct a list) builds
the keyed sublists that belong to the association list. Copy this version to the
Console window, press ENTER, and run (gp:getPointInput) again:
;; if you've made it this far, build the association list
;; as documented above. This will be the return value
;; from the function.

Examining Program Variables | 19
(list
(cons 10 StartPt)
(cons 11 EndPt)
(cons 40 (* HalfWidth 2.0))
(cons 50 (angle StartPt EndPt))
(cons 41 (distance StartPt EndPt))
)
)
)
)
)
Notice that, when building the list, the program converts the half width
specified by the user into a full width by multiplying its value by 2.
The Console window shows output similar to the following:
_$ (gp:getPointInput)
((10 2.16098 1.60116 0.0) (11 12.7126 7.11963 0.0) (40 . 0.592604)
(50 . 0.481876) (41 . 11.9076))
_$
Storing the Return Value of gp:getPointInput in a
Variable
Now try something else. Call the function again, but this time store the
return value in a variable named gp_PathData. To do this, enter the following
at the Console window prompt:
(setq gp_PathData (gp:getPointInput))
To view the value of the variable you just set, enter its name at the Console
window prompt:
_$ gp_PathData
VLISP returns data like the following:
((10 2.17742 1.15771 0.0) (11 13.2057 7.00466 0.0) (40 . 1.12747)
(50 . 0.487498) (41 . 12.4824))
Examining Program Variables
VLISP provides you with an entire toolkit of programming and debugging
tools. One of the most valuable tools is a Watch, which lets you examine vari-
ables in more detail than appears in the VLISP Console window. You can also
watch local variables within functions as the function executes.

To watch the value of a variable
1 Choose Debug ® Add Watch from the VLISP menu. VLISP displays a dialog
box titled “Add Watch.”
2 Enter the name of the variable you wish to examine. For this example, specify
gp_PathData, the variable you just set from the Console window. VLISP dis-
plays a Watch window:
VLISP displays the value of the variable on a single line within the Watch
window—the base window shown in the illustration. In this case, the value
of the variable is a long list, and you cannot see its entire value. You can resize
the Watch window by dragging its border, but there is a better alternative.
3 Double-click on the variable name in the Watch window. This opens an
Inspect window:
The Inspect window indicates the data type of the variable you are inspecting
(in this case, a list), and the value of the variable. For lists, Inspect displays
each list item on its own line.
4 Double-click on the line with the association list key 11. VLISP opens another
Inspect window:
5 When you are done inspecting variables, close all the Inspect windows but
keep the Watch window open.

Revising the Program Code | 21
Revising the Program Code
Now that you’ve seen how to use association lists in AutoLISP code, you can
use this method in writing the completed version of the gp:getPointInput
function. Using the following code, replace or modify the version of
gp:getPointInput you previously saved in gpmain.lsp.
NOTE If you need or want to type the code into gpmain.lsp, rather than copy
it from another file, you can save time by leaving out the comments (all lines that
begin with semicolons). But don’t get used to the idea of writing code without
comments!
;;;--------------------------------------------------------------;
;;; Function: gp:getPointInput ;
;;;--------------------------------------------------------------;
;;; Description: This function asks the user to select three ;
;;; points in a drawing, which will determine the ;
;;; path location, direction, and size. ;
;;;--------------------------------------------------------------;
;;; If the user responds to the get functions with valid data, ;
;;; use startPt and endPt to determine the position, length, ;
;;; and angle at which the path is drawn. ;
;;;--------------------------------------------------------------;
;;; The return value of this function is a list consisting of: ;
;;; (10 . Starting Point) ;; List of 3 reals (a point) denoting ;
;;; ;; starting point of garden path. ;
;;; (11 . Ending Point) ;; List of 3 reals (a point) denoting ;
;;; ;; ending point of garden path. ;
;;; (40 . Width) ;; Real number denoting boundary ;
;;; ;; width. ;
;;; (41 . Length) ;; Real number denoting boundary ;
;;; ;; length. ;
;;; (50 . Path Angle) ;; Real number denoting the angle ;
;;; ;; of the path, in radians. ;
;;;--------------------------------------------------------------;
;; if you've made it this far, build the association list
;; as documented above. This will be the return value
;; from the function.
(list
(cons 10 StartPt)
(cons 11 EndPt)
(cons 50 (angle StartPt EndPt))
(cons 41 (distance StartPt EndPt))
) ) ) ) )

Next, you need to update the main function, C:GPath, in gpmain.lsp. Modify
it to look like the following code:
(defun C:GPath (/ gp_PathData)
;; direction, then for path parameters. Continue only if you
;; have valid input. Store the data in gp_PathData.
(if (setq gp_PathData (gp:getPointInput))
(if (gp:getDialogInput)
(progn
;; At this point, you have valid input from the user.
;; pointer in the variable called PolylineName.
(princ ">")
) ;_ end of progn
) ;_ end of if
) ;_ end of if
);_ end of defun
If you are copying and pasting the code, add the following comments as a
header preceding C:GPath:

Revising the Program Code | 23
;;;**************************************************************;
;;; Function: C:GPath The Main Garden Path Function ;
;;;--------------------------------------------------------------;
;;; Description: This is the main garden path function. It is a ;
;;; C: function, meaning that it is turned into an ;
;;; AutoCAD command called GPATH. This function ;
;;; determines the overall flow of the garden path ;
;;; program. ;
;;;**************************************************************;
;;; The gp_PathData variable is an association list of the form: ;
;;; (10 . Starting Point) - List of 3 reals (a point) denoting ;
;;; starting point of the garden path. ;
;;; (11 . Ending Point) - List of 3 reals (a point) denoting ;
;;; endpoint of the garden path. ;
;;; (40 . Width) - Real number denoting boundary ;
;;; width. ;
;;; (41 . Length) - Real number denoting boundary ;
;;; length. ;
;;; (50 . Path Angle) - Real number denoting the angle of ;
;;; the path, in radians. ;
;;; (42 . Tile Size) - Real number denoting the size ;
;;; (radius) of the garden path tiles. ;
;;; (43 . Tile Offset) - Spacing of tiles, border to border. ;
;;; ( 3 . Object Creation Style) ;
;;; - Object creation style indicates how ;
;;; the tiles are to be drawn. The ;
;;; expected value is a string and one ;
;;; one of three values (string case ;
;;; is unimportant): ;
;;; "ActiveX" ;
;;; "Entmake" ;
;;; "Command" ;
;;; ( 4 . Polyline Border Style) ;
;;; - Polyline border style determines ;
;;; the polyline type to be used for ;
;;; path boundary. The expected value ;
;;; one of the following (string case is;
;;; unimportant): ;
;;; "Pline" ;
;;; "Light" ;
;;;**************************************************************;
To test the code revisions
1 Save the updated file.
2 Use the Check feature to search for any syntactical errors.
3 Format the code, to make it more readable.
4 Load the code, so that VLISP redefines the earlier versions of the functions.
5 To run the program, enter (c:gpath) at the Console prompt.
If the program does not run successfully, try fixing it and running it again.
Repeat until you are too frustrated to continue. If all else fails, you can copy
the correct code from the TutorialVisualLISPLesson2 directory.

Commenting Program Code
VLISP treats any AutoLISP statement beginning with a semicolon as a com-
ment. The last two code examples contained a lot of comments. A comment
in an AutoLISP program is something you write for yourself, not for the pro-
gram. Commenting code is one of the best programming practices you can
establish for yourself. Why write comments?
s To explain the code to yourself when you are editing the program nine
months in the future, adding all those features your users have been
asking you about. Memory fades, and the most apparent sequence of func-
tions can easily turn into an unrecognizable tangle of parentheses.
s To explain the code to others who inherit the responsibility of updating
the program. Reading someone else’s code is an extremely frustrating
experience, especially if the code contains very few comments.
VLISP contains some utilities that help you as you comment your code.
Notice some comments in the examples begin with three semicolons (;;;),
sometimes two (;;), and sometimes just one (;). Refer to “Applying Visual LISP
Comment Styles” in the Visual LISP Developer’s Guide to see how VLISP treats
the different comments.
To save space and trees, the remaining code examples in this tutorial do not
include all the comments in the sample source files. It is assumed you have
already established the beneficial habit of extensive commenting and will do
so without any prompting.
Setting a Breakpoint and Using More
Watches
A breakpoint is a symbol (point) you place in source code to indicate where
you want a program to stop executing temporarily. When you run your code,
VLISP proceeds normally until it encounters a breakpoint. At that point,
VLISP suspends execution and waits for you to tell it what to do. It hasn’t
halted the program for good—it has placed it in a state of suspended
animation.

Setting a Breakpoint and Using More Watches | 25
While your program is suspended, you can
s Step through your code, function by function, or expression by
expression.
s Resume normal execution of your program at any point.
s Alter the value of variables dynamically, and change the results of the
program being executed.
s Add variables to the Watch window.
Using the Debug Toolbar
The Debug toolbar contains several tools you will employ as you work
through this section. By default, this toolbar is attached to the View and
Tools toolbars, and appears as a single VLISP toolbar:
The Debug toolbar is the left-most set of icons. Most of the items on the tool-
bar are inactive until you run your program in debugging mode (that is, with
one or more breakpoints defined).
If you haven’t done so already, detach the Debug toolbar from its position at
the top of the screen. To do this, grab and drag it by the two vertical grips at
the left of the toolbar. You can detach any of the VLISP toolbars and position
them on your screen where they are most effective for your style of work.
The Debug toolbar is divided into three main groups of buttons, each con-
sisting of three buttons. When you run a program in debugging mode, the
toolbar looks like the following:
s The first three buttons allow you to step through your program code.
s The next three buttons determine how VLISP should proceed whenever it
has stopped at a breakpoint or an error.
s The next three buttons set or remove a breakpoint, add a Watch, and jump
to the position within your source code where the last break occurred.
Debug toolbar grips

The last button on the Debug toolbar is a Step Indicator. It does not execute
any function but provides a visual indication of where your cursor is
positioned as you step through your code. When you are not running in
debugging mode, this button appears blank.
To set a breakpoint
1 In the VLISP editor window containing gpmain.lsp, position your cursor just
in front of the opening parenthesis of the setq function of the following line
of code, within the gp:getPointInput function:
(setq HalfWidth (getdist EndPt "nHalf width of path: "))
2 Click the mouse once. The position is illustrated in the following screen
snapshot:
3 With the text insertion point set, press the Toggle Breakpoint button on the
Debug toolbar.
The Toggle Breakpoint button acts as a toggle, alternating between on and off
states. If there is no breakpoint at the cursor position, it sets one; if there is
already a breakpoint there, it removes it.
4 Press the Load Active Edit Window button on the Tools toolbar to load the
file.
5 Run the (C:GPath) function from the VLISP Console prompt.
VLISP executes the program normally up to the breakpoint. In this case, it
will prompt you for the first two points—the start point and endpoint of the
path.
6 Specify the start point and endpoint when prompted.

After you specify the points, VLISP suspends execution of the program and
returns focus to the text editor window, highlighting the line of code at the
breakpoint position:
There are a couple of things to notice:
s The cursor is located right at the breakpoint. This may be difficult to
notice, so VLISP provides another clue.
s In the Debug toolbar, the Step Indicator icon displays a red I-beam cursor
in front of a pair of parentheses. This indicates the VLISP debugger is
stopped before the expression.
Stepping through Code
There are three buttons you can use to step through your code. These are the
three left-most icons on the Debug toolbar. In sequence, they represent the
following actions:
s Step in to the highlighted expression.
s Step over to the end of the highlighted expression.
s Step out to the end of the function where you are currently stopped.
Before you make a selection, take another look at the status of the high-
lighted code, the cursor position, and the Step Indicator button. In summary:
An expression is highlighted, consisting of a getdist function nested within
a setq function, and the cursor is positioned at the very beginning of the
highlighted block.

To step through the code from the breakpoint
1 Press the Step Over button.
After you press the Step Over button, control passes to AutoCAD and you are
prompted to specify the width of the path.
2 Reply to the prompt.
After you specify the width, control passes back to VLISP. Notice where your
cursor is and what the step indicator button shows.
VLISP evaluates the entire highlighted expression, then stops at the end of
the expression.
3 Press the Step Over button again. VLISP jumps to the beginning of the next
block of code, and highlights the entire block.
4 Press the Step Into (not Step Over) button.

NOTE During this exercise, if you make an incorrect selection and skip a step
or two, you can restart the exercise very easily. First, press the Reset button from
the Debug toolbar. This terminates the execution of any VLISP code, and resets
the VLISP system to the top level. Next, start over at step 1.
Now the first cons function is highlighted, and VLISP is stopped right before
the function (notice the Step Indicator button).
Watching Variables As You Step through a
Program
While you step through your program, you can add variables to the Watch
window and change their values.
If you do not see the Watch window, simply press the Watch Window button
on the toolbar to bring it back.
If your Watch window stills contains the variable gp_PathData, press the
Clear Window button displayed at the top of the Watch window.
To add variables to the Watch window
1 Double-click on any occurrence of StartPt in the VLISP text editor window.
This is the name of the variable whose value you want to track.
2 Press the Add Watch button in the Watch window, or right-click and choose
Add Watch.
3 Repeat this process for the variables EndPt and HalfWidth. Your Watch win-
dow should resemble the following:

If you are debugging a program that isn’t working correctly, use breakpoints
in combination with watches to make sure your variables contain the values
you expect.
If a variable does not contain the value you think it should, you can change
the value and see how it affects the program. For example, say that you
expect the halfwidth value to be a whole number. But because you weren’t
careful about picking the points during the input selections, you ended up
with a value like 1.94818.
To change the value of a variable while the program is running
1 Enter the following at the Console prompt:
(setq halfwidth 2.0)
Note that the value in the Watch window changes. But can you be sure the
new value will be used when the width sublist (40 . width) is created in the
association list? Add one more expression to the Watch window to test this.
2 Choose Debug ® Watch Last Evaluation from the VLISP menu.
This adds a variable named *Last-Value* to your Watch window.
*Last-Value* is a global variable in which VLISP automatically stores the
value of the last expression evaluated.
3 Step through the program (pressing either the Step Into or Step Over button)
until the expression responsible for building the width sublist is evaluated.
The code for this action is:
If you overrode the value of HalfWidth as specified, the evaluation of this
expression should return (40 . 4.0) in the Watch window.
Stepping Out of the gp:getPointInput Function
and into C:Gpmain
There is one more point to illustrate: what happens to the value of the local
variables in gp:getPointInput after you exit the function.

To exit gp:getPointInput and return control to c:gpath
1 Press the Step Out button.
VLISP steps to the very end of the gp:getPointInput function and stops just
before exiting.
2 Press the Step Into button.
Control returns to c:gpmain, the function that called gp:getPointInput.
Examine the values of the variables in the Watch window. Because they are
variables local to the gp:getPointInput function, endpt and StartPt are nil.
VLISP automatically reclaimed the memory occupied by these variables.
Normally, the third local function variable HalfWidth also contains a value
of nil, but due to debugging activity, it was overridden globally in the
Console window and still possesses the value 2.0 in the Watch window. Also
the global *Last-Value* variable displays the association list constructed by
gp:getPointInput.
Your first debugging session iscomplete. But don’t forget your program isstill
in suspended animation.
To complete this lesson
1 Press the Continue button on the Debug toolbar. Respond to the prompts.
This runs the program to completion.
2 Choose Debug ® Clear All Breakpoints from the VLISP menu. Respond “yes”
to the prompt. This removes all the breakpoints within your code.
Remember: you can remove individual breakpoints by positioning the cursor
at the breakpoint and pressing the Toggle Breakpoint button.

In this lesson, you
s Learned about local and global variables.
s Set and removed breakpoints in a program.
s Stepped through a program while it was executing.
s Watched and dynamically changed the value of program variables during
execution.
s Saw how local variables are reset to nil after the function that defined
them completes its run.
The tools you learned in this lesson will be part of your daily work if you
intend to develop AutoLISP applications with VLISP.

In This Lesson
33
3
Drawing the Path Boundary
In this lesson, you will expand your program so it actu-
ally draws something within AutoCAD—the polyline
outline of the garden path. To draw the border, you
must create some utility functions that are not specific
to a single application but are general in nature and
may be recycled for later use. You will also learn about
writing functions that accept arguments—data that is
passed to the function from the outside—and why the
use of arguments is a powerful programming concept.
By the end of the lesson, you will draw an AutoCAD
shape parametrically, which means dynamically
drawing a shape based on the unique data parameters
provided by the user.
s Planning Reusable Utility
Functions
s Drawing AutoCAD Entities
s Enabling the Boundary Outline
Drawing Function

34 | Lesson 3 Drawing the Path Boundary
Planning Reusable Utility Functions
Utility functions perform tasks common to many applications you will be
writing. These functions form a tool kit you can use over and over again.
When you create a function as part of a tool kit, spend some time document-
ing it thoroughly. In your comments, also note the features you would like
to add to the function in the future, should time permit.
Converting Degrees to Radians
You will now create a function to prevent you from repetitively typing an
equation. It looks like this:
(defun Degrees->Radians (numberOfDegrees)
(* pi (/ numberOfDegrees 180.0)))
This function is called Degrees->Radians. The function name indicates its
purpose.
Why do you need a function to convert angular measurements? Behind the
scenes, AutoCAD uses radian angular measurement to keep track of angles,
whereas most people think in terms of degrees. This function in your toolkit
allows you to think in degrees, and lets AutoLISP convert those numbers to
radians.
To test the utility function
1 Enter the following at the VLISP Console prompt:
(degrees->radians 180)
The function returns the number 3.14159. According to how this function
works, 180 degrees is equivalent to 3.14159 radians. (Does that number ring
a bell? If so, treat yourself to a piece of pi.)
To use this function within your program, simply copy the function defini-
tion from the Console window into your gpmain.lsp file. You can paste it
anywhere in the file, as long as you do not paste it into the middle of an exist-
ing function.
To clean up your work, select the text you just pasted in, then press the
Format Selection button; VLISP will properly indent and format the code.

Planning Reusable Utility Functions | 35
Next, add some comments describing the function. When you have fully
documented the function, your code should look something like this:
;;;--------------------------------------------------------------;
;;; Function: Degrees->Radians ;
;;;--------------------------------------------------------------;
;;; Description: This function converts a number representing an ;
;;; angular measurement in degrees, into its radian ;
;;; equivalent. There is no error checking on the ;
;;; numberOfDegrees parameter -- it is always ;
;;; expected to be a valid number. ;
;;;--------------------------------------------------------------;
(* pi (/ numberOfDegrees 180.0))
)
Converting 3D Points to 2D Points
Another useful function in the garden path program converts 3D points to
2D points. AutoCAD usually works with 3D coordinates, but some entities,
such as lightweight polylines, are always meant to be 2D. The points
returned by the getpoint function are 3D, so you need to create a function
to convert them.
To convert a 3D point to a 2D point
1 Enter the following at the Console window prompt:
(defun 3dPoint->2dPoint (3dpt)(list (car 3dpt) (cadr 3dpt)))
2 Test the function by entering the following at the Console prompt:
(3dpoint->2dpoint (list 10 20 0))
This works, but there is another consideration for the garden path applica-
tion. Although it often doesn’t matter whether a number is an integer or a
real in LISP functions, this isn’t the case with ActiveX functions, which you’ll
use later in this lesson. ActiveX functions require real numbers. You can eas-
ily modify the function to ensure it returns reals instead of integers.
3 Enter the following code at the Console prompt:
(defun 3dPoint->2dPoint (3dpt)(list (float(car 3dpt))
(float(cadr 3dpt))))
4 Run the function again:
(3dpoint->2dpoint (list 10 20 0))
Notice the return values are now reals (indicated by the decimal values).

5 Test the function again, this time using the getpoint function. Enter the fol-
lowing at the Console prompt:
(setq myPoint(getpoint))
6 Pick a point in the AutoCAD graphics window.
The getpoint function returns a 3D point.
7 Enter the following at the Console prompt:
(3dPoint->2Dpoint myPoint)
Note the 2D point returned.
Now add the function to the gpmain.lsp file, just as you did with
Degrees->Radians. The new code should look like the following:
;;;--------------------------------------------------------------;
;;; Function: 3dPoint->2dPoint ;
;;;--------------------------------------------------------------;
;;; Description: This function takes one parameter representing a;
;;; 3D point (list of three integers or reals), and ;
;;; converts it into a 2D point (list of two reals).;
;;; There is no error checking on the 3D point ;
;;; parameter -- it is assumed to be a valid point. ;
;;;--------------------------------------------------------------;
;;; To do: Add some kind of parameter checking so that this ;
;;; function won’t crash a program if it is passed a ;
;;; null value, or some other kind of data type than a ;
;;; 3D point. ;
;;;--------------------------------------------------------------;
(defun 3dPoint->2dPoint (3dpt)
(list (float(car 3dpt)) (float(cadr 3dpt)))
)
Note that the function heading includes a comment about some work you
should do on this function in the future. If you want to earn some extra
credit, think about how you would go about foolproofing this function so
that invalid data does not make it crash.
Hint: numberp and listp functions…
(listp '(1 1 0)) => T
(numberp 3.4) => T

Drawing AutoCAD Entities | 37
Drawing AutoCAD Entities
Most AutoLISP programs draw entities using one of several methods:
s ActiveX functions
s The entmake function
s The command function
This lesson focuses on entity creation via ActiveX. In Lesson 5, you will
implement the entmake and AutoCAD command alternatives.
Creating Entities Using ActiveX Functions
The newest way of creating entities is by using the ActiveX functions within
VLISP. ActiveX has several advantages over entmake and command.
s ActiveX functions are faster.
s ActiveX function names indicate the action they perform, resulting in
easier readability, maintenance, and bug-fixing.
You will see an example of an ActiveX function later in this lesson.
Using entmake to Build Entities
The entmake function allows you to build an entity by gathering values for
things such as coordinate location and orientation, layer, and color into an
association list, then asking AutoCAD to build the entity for you. The associ-
ation list you build for the entmake function looks very much like the
association list you get back when you call the entget function. The differ-
ence is that entget returns information about an entity, while entmake builds
a new entity from raw data.
Using the AutoCAD Command Line
When AutoLISP first appeared in AutoCAD, the only available means for
entity creation was the command function. This allows an AutoLISP program-
mer to code just about any command that can be executed from the
AutoCAD Command prompt. This is reliable, but it is not as fast as ActiveX
methods and does not provide the flexibility of entmake.

Enabling the Boundary Outline Drawing
Function
After the last lesson, the gp:drawOutline function looked like the following:
;;;--------------------------------------------------------------;
;;; Function: gp:drawOutline ;
;;;--------------------------------------------------------------;
;;; Description: This function draws the outline of the ;
;;; garden path. ;
;;;--------------------------------------------------------------;
(defun gp:drawOutline ()
(alert
(strcat "This function will draw the outline of the polyline "
"nand return a polyline entity name/pointer."
)
)
;; For now, simply return a quoted symbol. Eventually, this
;; function will return an entity name or pointer.
'SomeEname
)
As it exists, the code does not do much. However, using the association list
information stored in the variable gp_PathData, you have enough informa-
tion to calculate the points for the path boundary. You now have to
determine how to pass the information in that variable to gp:drawOutline.
Remember gp_PathData is a local variable defined within the C:GPath
function. In AutoLISP, local variables declared in one function are visible to
any function called from that function (refer to “Differentiating between
Local and Global Variables” on page 14 for clarification). The
gp:drawOutline function is called from within C:GPath. You can refer to the
gp-PathData variable in gp:drawOutline, but this is not a good programming
practice.
Why? When the two functions using the same variable are defined in the
same file, as in the examples shown so far, it is not too difficult to figure out
where the variable is defined and what it is used for. But if the functions are
defined in different files—as is often the case—you would have to search
through both files to figure out what gp_PathData represents.
Passing Parameters to Functions
A better way to convey information from one function to another is to pass
parameters to the called function. Design the function so it expects to receive
a number of values. Remember the Degrees->Radians function? This func-
tion is passed a parameter named numberOfDegrees:

Enabling the Boundary Outline Drawing Function | 39
When you call the function, it expects you to pass it a number. The number
within Degrees->Radians is declared as the parameter named
numberOfDegrees. For example:
_$ (degrees->radians 90)
1.5708
In this case, the number 90 is assigned to the parameter numberOfDegrees.
You can also pass a variable to a function. For example, you might have a
variable called aDegreeValue that contains the number 90. The following
commands set aDegreeValue and pass the variable to Degrees->Radians:
_$ (setq aDegreeValue 90)
90
_$ (degrees->radians aDegreeValue)
1.5708
Working with an Association List
You can pass the association list in the gp_PathData variable to the
gp:drawOutline function by invoking the function as follows:
(gp:drawOutline gp_PathData)
Simple enough, but you also need to figure out how to process the informa-
tion stored in the association list. The VLISP Inspect feature can help you
determine what to do.
To use the VLISP Inspect feature to analyze your association list
1 Load the code that is in the text editor window.
2 Enter the following expression at the Console prompt:
(setq BoundaryData (gp:getPointInput))
VLISP will store the information you provide in a variable named
BoundaryData.
3 Respond to the prompts for start point, endpoint, and half width.
4 Select the BoundaryData variable name in the Console window by double-
clicking it.

5 Choose View ® Inspect from the VLISP menu.
VLISP displays a window like the following:
The Inspect window shows you each sublist within the BoundaryData
variable.
(assoc 50 BoundaryData)
The assoc function returns the entry in the association list that is identified
by the specified key. In this example, the specified key is 50; this is associated
with the angle of the garden path (see “Putting Association Lists to Use” on page
18 for a list of the key-value pairs defined for this application).
(cdr(assoc 50 BoundaryData))
The cdr function returns the second element, and any remaining elements
after that, from a list. In this example, cdr retrieves the angle value, which is
the second and last element in the entry returned by the assoc function.
By this point, you should have no trouble understanding the following code
fragment:
(setq PathAngle (cdr (assoc 50 BoundaryData))
Width (cdr (assoc 40 BoundaryData))
HalfWidth (/ Width 2.00)
StartPt (cdr (assoc 10 BoundaryData))
PathLength (cdr (assoc 41 BoundaryData))
Using Angles and Setting Up Points
There are still a couple of issues remaining. First, you need to figure out how
to draw the path at any angle the user specifies. From the gp:getPointInput
function, you can easily establish the primary angle of the path. To draw it,
you need a couple of additional vectors perpendicular to the primary angle.

This is where the Degrees->Radians function is useful. The following code
fragment demonstrates how you can set up your two perpendicular vectors
using the PathAngle variable as an argument passed to the Degrees->Radians
function:
(setq angp90 (+ PathAngle (Degrees->Radians 90))
angm90 (- PathAngle (Degrees->Radians 90)))
With the data you now have in hand, you can establish the four corner
points of the path using polar function:
(setq p1 (polar StartPt angm90 HalfWidth)
p2 (polar p1 PathAngle PathLength)
p3 (polar p2 angp90 Width)
p4 (polar p3 (+ PathAngle (Degrees->Radians 180))
The polar function returns a 3D point at a specified angle and distance from
a point. For instance, polar locates p2 by projecting p1 a distance of
PathLength along a vector oriented at an angle of PathAngle, counter-
clockwise from the x-axis.
pathAngle
angm90 (minus 90 degrees)
angp90 (plus 90 degrees)
p1
p4
p2
p3

Understanding the ActiveX Code in
gp:drawOutline
The gp:drawOutline function issues ActiveX calls to display the path’s
polyline border in AutoCAD. The following code fragment uses ActiveX to
draw the border:
;; Add polyline to the model space using ActiveX automation.
(setq pline (vla-addLightweightPolyline
*ModelSpace*; Global Definition for Model Space
VLADataPts; vertices of path boundary
) ;_ end of vla-addLightweightPolyline
) ;_ end of setq
(vla-put-closed pline T)
How do you make sense of this code? An essential resource is the ActiveX and
VBA Reference, which describes the methods and properties accessible to
ActiveX clients such as this garden path application. The “Working with
ActiveX” chapter of the Visual LISP Developer’s Guide explains how to trans-
late the VBA™
syntax in the ActiveX and VBA Reference into ActiveX calls in
AutoLISP syntax.
For the moment, though, you can gain a rudimentary understanding by
scrutinizing the pattern of the two vla- calls in the preceding example. The
names of all AutoLISP ActiveX functions that work on AutoCAD objects are
prefixed with vla-. For example, addLightweightPolyline is the name of an
ActiveX method, and vla-addLightweightPolyline is the AutoLISP function
that invokes this method. The vla-put-closed call updates the closed
property of the pline object, the polyline drawn by
vla-addLightweightPolyline.
The Automation objects that factor into AutoLISP ActiveX calls abide by a
few standard rules:
s The first argument to a vla-put, vla-get, or vla- method call is the
object being modified or queried, for example, *ModelSpace* in the first
function call and pline in the second call.
s The return value of a vla- method call is a VLA-object, which can be used
in subsequent calls. For example, vla-addLightweightPolyline yields a
return object, pline, that is altered in the next ActiveX call.
s The ActiveX object model is structured hierarchically. Objects are tra-
versed from the application object at the topmost level down to
individual drawing primitives, such as polyline and circle objects. Thus,
the gp:drawOutline function is not yet complete, because the
*ModelSpace* automation object must first be accessed via the root appli-
cation object.

Ensuring That ActiveX Is Loaded
ActiveX functionality is not automatically enabled when you start AutoCAD
or VLISP, so your programs must ensure that ActiveX is loaded. The following
function call accomplishes this:
(vl-load-com)
If ActiveX support is not yet available, executing vl-load-com initializes the
AutoLISP ActiveX environment. If ActiveX is already loaded, vl-load-com
does nothing.
Obtaining a Pointer to Model Space
When you add entities through ActiveX functions, you need to identify the
model space or paper space in which the entity is to be inserted. (In ActiveX
terminology, entities are objects, but this tutorial will continue using the term
entity.) To tell AutoCAD which space the new entities should occupy, you
need to obtain a pointer to that space. Unfortunately, obtaining a pointer to
model space is not a simple, single-shot function. The following code frag-
ment shows how the operation needs to be set up:
(vla-get-ModelSpace (vla-get-ActiveDocument
(vlax-get-Acad-Object)))
Working from the inside out, the vlax-get-Acad-Object function retrieves a
pointer to AutoCAD. This pointer is passed to the vla-get-ActiveDocument
function, which retrieves a pointer to the active drawing (document) within
AutoCAD. The Active Document pointer is then passed to the
vla-get-ModelSpace function that retrieves a pointer to the model space of
the current drawing.
This is not the kind of expression you want to type over and over. For exam-
ple, look at how much more complicated the code for adding a polyline
using ActiveX appears when the entire model space expression is used:
(vla-get-ModelSpace
(vla-get-ActiveDocument
(vlax-get-Acad-Object)
)
)
VLADataPts)
)
The function is definitely less understandable. Not only that, but within
every expression within your program where an entity is created, you repeat
the same set of nested functions. This demonstrates one of the few excellent

uses for global variables. The garden path application can add a lot of entities
to model space (think of all the tiles in the path), so, set up a global variable
to store the pointer to the model space, as in the following code:
(setq *ModelSpace* (vla-get-ModelSpace (vla-get-ActiveDocument
(vlax-get-Acad-Object))))
You can use the variable *ModelSpace* anytime you call an ActiveX entity
creation function. The only tricky thing with this scheme is the
*ModelSpace* variable must be ready to go before you start drawing. For this
reason, the setq establishing this variable will be called at the time the
application is loaded, immediately after the call to vl-load-com. These calls
will be placed before any defun in the program file. As a result, they are
executed as soon as the file is loaded.
Constructing an Array of Polyline Points
The last issue to deal with is how to transform the individual point vari-
ables—p1, p2, p3, and p4—into the format required for the
vla-addLightweightpolyline function. First, get some help on the topic.
To obtain information on a function
1 Press the Help button on the VLISP toolbar.
2 Enter vla-addLightweightpolyline in the Enter Item Name dialog box, and
press OK. (The Help system is not case sensitive, so do not worry about how
you capitalize the function name.)
Online Help states that AddLightWeightPolyline requires you to specify the
polyline vertices as an array of doubles in the form of a variant. Here is how
Help describes this parameter:
The array of 2D WCS coordinates specifying the vertices of the
polyline. At least two points (four elements) are required for
constructing a lightweight polyline. The array size must be a
multiple of 2.
A variant is an ActiveX construct that serves as a container for various types
of data. Strings, integers, and arrays can all be represented by variants. The
variant stores data along with the information identifying the data.
So far, you have four points, each in the format (x, y, z). The challenge is to
convert these four points into a list of the following form:
(x1 y1 x2 y2 x3 y3 x4 y4)

The append function takes multiple lists and concatenates them. To create a
list of the four points in the proper format for the ActiveX function, you can
use the following expression:
(setq polypoints (append (3dPoint->2dPoint p1)
(3dPoint->2dPoint p2)
(3dPoint->2dPoint p3)
(3dPoint->2dPoint p4)))
Writing the 3dPoint->2dPoint function four times is a bit cumbersome. You
can reduce the code further by using the mapcar and apply functions. When
selected, mapcar executes a function on individual elements in one or more
lists, and apply passes a list of arguments to the specified function. The
resulting code looks like the following:
(setq polypoints (apply 'append (mapcar '3dPoint->2dPoint
(list p1 p2 p3 p4))))
Before the call to mapcar, the list of points is in this form:
((x1 y1 z1) (x2 y2 z2) (x3 y3 z3) (x4 y4 z4))
After mapcar you have a list of points in the following form:
((x1 y1) (x2 y2) (x3 y3) (x4 y4))
And finally, after applying the append function on the list returned from
mapcar, you end up with the following:
(x1 y1 x2 y2 x3 y3 x4 y4)
Constructing a Variant from a List of Points
So far, the data in the polypoints variable is in a list format suitable for many
AutoLISP calls. However, the data is to be supplied as an input parameter to
an ActiveX call that expects a variant array of doubles. You can use another
utility function to make the required conversion from list to variant:
(defun gp:list->variantArray (ptsList / arraySpace sArray)
; allocate space for an array of 2d points stored as doubles
(setq arraySpace (vlax-make-safearray
vlax-vbdouble ; element type
(cons 0
(- (length ptsList) 1)
) ; array dimension
)
)
(setq sArray (vlax-safearray-fill arraySpace ptsList))
; return array variant
(vlax-make-variant sArray)
)

The following actions take place in gp:list->variantArray:
s The vlax-make-safearray function is called to allocate an array of dou-
bles (vlax-vbdouble). The vlax-make-safearray function also requires
you to specify the lower and upper index boundaries of the array. In
gp:list->variantArray, the call to vlax-make-safearray specifies a start
index of 0 and sets the upper limit to one less than the number of ele-
ments passed to it (ptsList).
s The vlax-safearray-fill function is called to populate the array with
the elements in the point list.
s The vlax-make-variant is called to convert the safearray into a variant. As
the last function call in gp:list->variantArray, the return value is passed
to the calling function.
The following is an example of a function call that invokes
gp:list->variantArray to convert a list to a variant array of doubles:
; data conversion from list to variant
(setq VLADataPts (gp:list->variantArray polypoints))
Putting It All Together
You now have all the code you need to draw the outline of the garden path.
To update your code
1 Replace your old code for the gp:drawOutline function with the following:
;;;---------------------------------------------------------------
;;; Function: gp:drawOutline
;;;---------------------------------------------------------------
;;; Description: This function will draw the outline of the garden
;;; path.
;;;---------------------------------------------------------------
;;; Note: No error checking or validation is performed on the
;;; BoundaryData parameter. The sequence of items within this
;;; parameter does not matter, but it is assumed that all sublists
;;; are present and contain valid data.
;;; --------------------------------------------------------------
(defun gp:drawOutline (BoundaryData / VLADataPts PathAngle
Width HalfWidth StartPt PathLength
angm90 angp90 p1 p2
p3 p4 polypoints pline
)

;; extract the values from the list BoundaryData
angp90 (+ PathAngle (Degrees->Radians 90))
angm90 (- PathAngle (Degrees->Radians 90))
p1 (polar StartPt angm90 HalfWidth)
p4 (polar p3 (+ PathAngle (Degrees->Radians 180)) PathLength)
polypoints (apply 'append
(mapcar '3dPoint->2dPoint (list p1 p2 p3 p4))
)
)
;; ***** data conversion *****
;; Notice, polypoints is in AutoLISP format, consisting of a list
;; of the 4 corner points for the garden path.
;; The variable needs to be converted to a form of input parameter
;; acceptable to ActiveX calls.
(setq VLADataPts (gp:list->variantArray polypoints))
*ModelSpace*; Global Definition for Model Space
VLADataPts
) ;_ end of setq
;; Return the ActiveX object name for the outline polyline
;; The return value should look something like this:
;; #<VLA-OBJECT IAcadLWPolyline 02351a34>
pline
) ;_ end of defun
Note that gp:drawOutline now returns the variable pline, not the quoted
symbol 'SomeEname used in the stubbed-out version of the function.
2 Format the code you just entered by selecting it and pressing the Format
Selection button on the VLISP toolbar.

3 Enable ActiveX and add the global variable assignment for the pointer to
model space, as described earlier. Scroll to the top of the text editor window
and add the following code before the first defun:
;;;--------------------------------------------------------------
;;; First step is to load ActiveX functionality. If ActiveX support
;;; already exists in document (can occur when Bonus tools have been
;;; loaded into AutoCAD), nothing happens. Otherwise, ActiveX
;;; support is loaded.
;;;---------------------------------------------------------------
(vl-load-com)
;;; In Lesson 4, the following comment and code is moved to utils.lsp
;;;---------------------------------------------------------------
;;; For ActiveX functions, we need to define a global variable that
;;; "points" to the Model Space portion of the active drawing. This
;;; variable, named *ModelSpace* will be created at load time.
;;;---------------------------------------------------------------
(setq *ModelSpace*
(vla-get-ModelSpace
(vla-get-ActiveDocument (vlax-get-acad-object))
) ;_ end of vla-get-ModelSpace
) ;_ end of setq
Note how the above code lives outside of any defun. Because of this, VLISP
automatically executes the code at the time you load the file.
4 Look for the following line in the C:GPath function:
Change it to the following:
(setq PolylineName (gp:drawOutline gp_PathData))
The gp:drawOutline function is now expecting a parameter—the list con-
taining the polyline boundary data—and this change fulfills that
requirement.
5 Add the gp:list->variantArray function shown in “Constructing a Variant
from a List of Points” on page 45 to the end of gpmain.lsp.
Try loading and running the revised program. VLISP takes control away from
AutoCAD before you see the end result, so switch back to the AutoCAD win-
dow after control returns to VLISP. If the program ran correctly, you should
see a border for the garden path. If you find errors, debug the code and try
again.

Wrapping Up Lesson 3 | 49
In this lesson, you
s Wrote utility functions that can be reused in other applications.
s Added entity creation logic to your program.
s Learned how to use ActiveX functions.
s Learned how to work with association lists.
s Enabled your program to draw a garden path border.
If you’re confused about anything from this lesson, it is recommended you
go through it once again before moving on to Lesson 4. (If you decide to do
so, copy the completed code from your Lesson2 directory so that you start the
lesson from the correct place.) And if all else fails, you can always copy the
code from the TutorialVisualLISPLesson3 directory.

In This Lesson
51
4
Creating a Project and
Adding the Interface
In this lesson, you will accomplish two major tasks: cre-
ating a VLISP project and adding a dialog-based inter-
face to your application. In the process, you will split
the single AutoLISP file you worked with so far
(gpmain.lsp) into several smaller files, reinforcing the
concept of code modularity.
From this lesson on, the tutorial provides more general
descriptions of the tasks you need to perform, unless
new topics are covered. Also, the code fragments will be
minimally documented to save space. This, however,
does not absolve you from your moral obligation to
fully document your code!
s Modularizing Your Code
s Using Visual LISP Projects
s Adding the Dialog Box Interface
s Interacting with the Dialog Box
from AutoLISP Code
s Providing a Choice of Boundary
Line Type
s Cleaning Up
s Running the Application

52 | Lesson 4 Creating a Project and Adding the Interface
Modularizing Your Code
As a result of the work you did in Lesson 3, your gpmain.lsp file was getting
rather large. This is not a problem for VLISP, but it is easier to maintain the
code if you split things up into files containing logically related functions.
It’s also easier to debug your code. For example, if you have a single file with
150 functions, a single missing parenthesis can be difficult to find.
In the tutorial, the files will be organized as follows:
To split gpmain.lsp into four files
1 Create a new file, then cut and paste the following functions from gpmain.lsp
into the new file:
s gp:getPointInput
s gp:getDialogInput
Save the new file in your working directory as gp-io.lsp.
2 Create a new file, then cut and paste the following functions from gpmain.lsp
into the new file:
s Degrees->Radians
s 3Dpoint->2Dpoint
s gp:list->variantArray
Tutorial file organization
File name Contents
GP-IO.LSP All input and output (I/O) functions) such as getting user input. Also
contains the AutoLISP code required for the dialog box interface you
will be adding.
UTILS.LSP Includes all generic functions that can be used again on other
projects. Also contains load-time initializations.
GPDRAW.LSP All drawing routines—the code that actually creates the AutoCAD
entities.
GPMAIN.LSP The basic C:GPath function.

Using Visual LISP Projects | 53
Also, at the beginning of the file, insert the lines of code to establish ActiveX
functionality (vl-load-com) and commit global variable assignment
(*ModelSpace*).
Save the file as utils.lsp.
3 Create a new file, then cut and paste the following function from gpmain.lsp
into the new file:
s gp:drawOutline
Save this file as gpdraw.lsp.
4 After stripping the code out of gpmain.lsp, save it and check it. Only the orig-
inal function, C:GPath, should remain in the file.
Your VLISP desktop is starting to get crowded. You can minimize any window
within VLISP and it stays accessible. Press the Select Window button on the
toolbar to choose a window from a list, or choose Window from the VLISP
menu and select a window to view.
Using Visual LISP Projects
The VLISP project feature provides a convenient way to manage the files that
make up your application. And with the project feature, you can open a
single project file instead of individually opening every LISP file in the
application. Once the project is open, getting to its constituent files is a
double-click away.
To create a VLISP project
1 Choose Project ® New Project from the VLISP menu.
2 Save the file in your Lesson4 directory, using the name gpath.prj.
After you save the file, VLISP displays the Project Properties dialog box.

3 Press the [Un]Select All button on the left in the Project Properties dialog box.
4 Press the button containing an arrow pointing to the right. This adds all the
selected files to your project.
In the Project Properties dialog box, the list box on the left shows all LISP files
that reside in the same directory as your project file and are not included in
that project. The list box on the right lists all the files that make up the
project. When you add the selected files to the project, those file names move
from the left box to the right box.
5 In the list box on the right side of the dialog box, select gpmain, then press
the Bottom button. This moves the file to the bottom of the list.
VLISP loads project files in the order they are listed. Because the prompt that
tells users the name of the command is located at the end of the gpmain.lsp
file, you need to move this file to the bottom of the list. Loading this file last
results in the prompt displayed to users. The utils.lsp file should be loaded
first because it contains initialization code for the application. Therefore,
select utils in the dialog’s list box and press the Top button.
6 Press OK.

Adding the Dialog Box Interface | 55
VLISP adds a small project window to your VLISP desktop. The window lists
the files in your project. Double-click on any file to open the file in the VLISP
text editor (if it is not already open) and make it the active editor window.
Adding the Dialog Box Interface
The next part of this lesson concerns adding a dialog box interface to the gar-
den path application. To do this, you will be working with another language,
dialog control language (DCL).
Currently, your gpath function only accepts input at the Command line. You
included a stubbed-out function (gp:getDialogInput) with the intention of
adding a dialog box interface. Now is the time to add the interface.
There are two steps in creating a functional dialog interface:
s Define the appearance and contents of the dialog boxes.
s Add program code to control dialog behavior.
The description and format of a dialog box is defined in a .dcl file. In the
Visual LISP Developer’s Guide, DCL is described in chapter 11, “Designing Dia-
log Boxes,” chapter 12, “Managing Dialog Boxes,” and chapter 13, “Program-
mable Dialog Box Reference.”
Program code that initializes default settings and responds to user interaction
will be added to gp:getDialogInput.
Defining the Dialog Box with DCL
Begin by taking a look at the dialog box you need to create.

The dialog box contains the following elements:
s Two sets of radio buttons.
One set of buttons determines the polyline style of the boundary, and the
other set of buttons specifies the tile entity creation method (ActiveX,
entmake, or command). Only one radio button in a set can be selected at one
time.
s Edit boxes for specifying the radius of tiles and the spacing between tiles.
s A standard set of OK and Cancel buttons.
Dialog box components are referred to as tiles in DCL. Writing the complete
contents of a dialog box DCL file may seem overwhelming. The trick is to
sketch out what you want, break it down into sections, then write each
section.
To define the dialog box
1 Open a new file in the VLISP text editor window.
2 Enter the following statement in the new file:
label = "Garden Path Tile Specifications";
This DCL statement defines the title of the dialog box window.
3 Define the radio buttons for specifying polyline type by adding the following
code:
: boxed_radio_column { // defines the radio button areas
label = "Outline Polyline Type";
: radio_button { // defines the lightweight radio button
label = "&Lightweight";
key = "gp_lw";
value = "1";
}
: radio_button { // defines the old-style polyline radio button
label = "&Old-style";
key = "gp_hw";
}
}
The boxed_radio_column DCL directive defines a box boundary and allows
you to specify a label for the set of buttons. Within the boundary, you specify
the radio buttons you need by adding radio_button directives. Each radio
button requires a label and a key. The key is the name by which your
AutoLISP code can refer to the button.
Notice that the radio button labeled “lightweight” is given a value of 1. A
value of 1 (a string, not an integer) assigned to a button makes it the default
choice in a row of buttons. In other words, when you first display the dialog,
this button will be selected. Also notice that in DCL files, double-slash char-
acters, not semicolons as in AutoLISP, indicate a comment.

Adding the Dialog Box Interface | 57
4 Define the radio column for the selection of the entity creation style by add-
ing the following code:
: boxed_radio_column { // defines the radio button areas
label = "Tile Creation Method";
: radio_button { // defines the ActiveX radio button
label = "&ActiveX Automation";
key = "gp_actx";
value = "1";
}
: radio_button { // defines the (entmake) radio button
label = "&Entmake";
key = "gp_emake";
}
: radio_button { // defines the (command) radio button
label = "&Command";
key = "gp_cmd";
}
}
5 Add the following code to define the edit box tiles that allow users to enter
the numbers specifying tile size and spacing:
: edit_box { // defines the Radius of Tile edit box
label = "&Radius of tile";
key = "gp_trad";
edit_width = 6;
}
: edit_box { // defines the Spacing Between Tiles edit box
label = "S&pacing between tiles";
key = "gp_spac";
edit_width = 6;
}
Notice that this definition does not set any initial values for the edit boxes.
You will set default values for each edit box in your AutoLISP program.
6 Add the following code for the OK and Cancel buttons:
: row { // defines the OK/Cancel button row
: spacer { width = 1; }
: button { // defines the OK button
label = "OK";
is_default = true;
key = "accept";
width = 8;
fixed_width = true;
}
: button { // defines the Cancel button
label = "Cancel";
is_cancel = true;
key = "cancel";
width = 8;
fixed_width = true;
}
: spacer { width = 1;}
}
Both buttons are defined within a row, so they line up horizontally.

7 Scroll to the beginning of the text editor window and insert the following
statement as the first line in your DCL:
gp_mainDialog : dialog {
8 The dialog directive requires a closing brace, so scroll to the end of the file
and add the brace as the last line of DCL code:
}
Saving a DCL File
Before saving the file containing your DCL, consider the fact that AutoCAD
must be able to locate your DCL file during runtime. For this reason, the file
must be placed in one of the AutoCAD Support File Search Path locations. (If
you are unsure about these locations, choose Tools ® Options from the
AutoCAD menu and examine the Support File Search Path locations under
the Files tab.)
For now, you can save the file in the AutoCAD Support directory.
To save your DCL file
1 Choose File ® Save As from the VLISP menu.
2 In the Save As Type field of the Save As dialog box, choose DCL Source Files
from the pull-down menu.
3 Change the Save In path to <AutoCAD directory>Support.
4 Enter the file name gpdialog.dcl.
5 Press Save.
Notice VLISP changes the syntax coloring scheme after you save the file.
VLISP is designed to recognize DCL files and highlight the different types of
syntactical elements.
Previewing a Dialog Box
VLISP provides a preview feature for checking the results of your DCL coding.
To preview a dialog box defined with DCL
1 Choose Tools ® Interface Tools ® Preview DCL in Editor from the VLISP
menu.
2 Press OK when prompted to specify a dialog name.
In this case, your DCL file defines just a single dialog box, so there is no
choice to be made. As you create larger and more robust applications, how-

Interacting with the Dialog Box from AutoLISP Code | 59
ever, you may end up with DCL files containing multiple dialog boxes. This
is where you can select which one to preview.
3 If the dialog box displays successfully, press any button to end the dialog.
VLISP passes control to AutoCAD to display the dialog box. If AutoCAD finds
syntactical errors, it displays one or more message windows identifying the
errors.
If AutoCAD detects DCL errors and you are unable to figure out how to fix
them, copy the gpdialog.dcl file in your TutorialVisualLISPLesson4 directory
and save it in the Support directory.
Interacting with the Dialog Box from
AutoLISP Code
You now need to program your AutoLISP function to interact with the dialog
box. The stubbed-out function, gp:getDialogInput, is where this activity
will take place. This function now lives in the gp-io.lsp file, which you earlier
extracted from gpmain.lsp.
Developing a dialog box interface can be confusing the first few times you do
it. It involves planning ahead and asking yourself such questions as:
s Does the dialog box need to be set up with default values?
s What happens when the user presses a button or enters a value?
s What happens when the user presses Cancel?
s If the dialog (.dcl) file is missing, what needs to occur?
Setting Up Dialog Values
When you run the complete garden path application, notice that the dialog
box always starts up with ActiveX as the default object creation method and
Lightweight as the polyline style. Something more interesting occurs with
the default tile size—the values change depending on the width of the path.
The following code fragment shows how to set up the default values to be dis-
played in the dialog box:
(setq objectCreateMethod "ACTIVEX"
plineStyle "LIGHT"
tilerad (/ pathWidth 15.0)
tilespace (/ tilerad 5.0)
dialogLoaded T
dialogShow T
) ;_ end of setq

For the moment, don’t worry about what purpose the dialogLoaded and
dialogShow variables serve. This becomes apparent in the next two sections.
Loading the Dialog File
Your program first needs to load the DCL file using the load_dialog
function. This function searches for dialog files according to the AutoCAD
support file search path, unless you specify a full path name.
For every load_dialog function there should be a corresponding
unload_dialog function later in the code. You will see this in a moment. For
now, take a look at how you need to load in your dialog:
;; Load the dialog box. Set up error checking to make sure
;; the dialog file is loaded before continuing
(if (= -1 (setq dcl_id (load_dialog "gpdialog.dcl")))
(progn
;; There's a problem - display a message and set the
;; dialogLoaded flag to nil
(princ "nCannot load gpdialog.dcl")
(setq dialogLoaded nil)
) ;_ end of progn
) ;_ end of if
The dialogLoaded variable indicates if the dialog loaded successfully. In the
code where you set up the initial values for the dialog box, you set
dialogLoaded to an initial value of T. As you can see in the code fragment
above, dialogLoaded is set to nil if there is a problem with the load.
Loading a Specific Dialog into Memory
It was noted earlier that a single DCL file may contain multiple dialog box
definitions. The next step in using a dialog is to specify which dialog box def-
inition to display. The following code demonstrates this:
(if (and dialogLoaded
(not (new_dialog "gp_mainDialog" dcl_id))
) ;_ end of and
(progn
;; There's a problem...
(princ "nCannot show dialog gp_mainDialog")
(setq dialogShow nil)
) ;_ end of progn
) ;_ end of if
Notice how the and function is used to test if the dialog was loaded and if the
call to new_dialog was successful. If there are multiple expressions evaluated
within an and function call, evaluation of subsequent expressions is

terminated with the first expression that evaluates to nil. In this case, if the
dialogLoaded flag is nil (meaning the load function in the previous section
failed), VLISP does not attempt to perform the new_dialog function.
Notice that the code also accounts for the possibility that something might
not be working properly with the DCL file, and sets the dialogShow variable
to nil if that is the case.
The new_dialog function simply loads the dialog into memory—it does not
display it. The start_dialog function displays the dialog box. All dialog box
initialization, such as setting tile values, creating images or lists for list boxes,
and associating actions with specific tiles must take place after the
new_dialog call and before the start_dialog call.
Initializing the Default Dialog Values
If everything worked successfully in loading the dialog, you are ready to start
setting up the values that will be displayed to users. A successful load is indi-
cated if the flag variables dialogLoaded and dialogShow are both T (true).
Now set the initial values for the tile radius and spacing. The set_tile func-
tion assigns a value to a tile. An edit box deals with strings rather than
numbers, so you need to use the rtos (convert Real TO String) function to
convert your tile size variable values into strings in decimal format with a
precision of two digits. The following code handles this conversion:
(if (and dialogLoaded dialogShow)
(progn
;; Set the initial state of the tiles
(set_tile "gp_trad" (rtos tileRad 2 2))
(set_tile "gp_spac" (rtos tileSpace 2 2))
Assigning Actions to Tiles
A DCL definition does nothing more than define a lifeless dialog box. You
connect this lifeless dialog box to your dynamic AutoLISP code with the
action_tile function, as demonstrated by the following code:
;; Assign actions (the functions to be invoked) to dialog buttons
(action_tile
"gp_lw"
"(setq plineStyle "Light")"
)
(action_tile
"gp_hw"
"(setq plineStyle "Pline")"
)

(action_tile
"gp_actx"
"(setq objectCreateMethod "ActiveX")"
)
(action_tile
"gp_emake"
"(setq objectCreateMethod "Entmake")"
)
(action_tile
"gp_cmd"
"(setq objectCreateMethod "Command")"
)
(action_tile "cancel" "(done_dialog) (setq UserClick nil)")
(action_tile
"accept"
(strcat "(progn (setq tileRad (atof (get_tile "gp_trad")))"
"(setq tileSpace (atof (get_tile "gp_spac")))"
"(done_dialog) (setq UserClick T))"
)
)
Notice all the quotes around the AutoLISP code. When you write an AutoLISP
action_tile function, your code is essentially telling a tile, “here, remember
this string, then pass it back to me when the user selects you.” The string
(anything within double-quotation marks) is dormant until the user selects
the tile. At that time, the tile passes the string to AutoCAD, which converts
the string into functioning AutoLISP code and executes the code.
For example, consider the following action_tile expression, which is con-
nected to the lightweight polyline radio button:
(action_tile
"gp_lw"
"(setq plineStyle "Light")"
)
The code assigns the string "(setq plineStyle "Light")" to the radio but-
ton. When a user picks the button, the string is passed back to AutoCAD and
transformed directly into the following AutoLISP expression:
(setq plineStyle "Light")
Look at one more code fragment. The following is the action_tile expres-
sion assigned to the OK button:
(action_tile
"accept"
(strcat "(progn (setq tileRad (atof (get_tile "gp_trad")))"
"(setq tileSpace (atof (get_tile "gp_spac")))"
"(done_dialog) (setq UserClick T))"
)

When a user presses the OK button, the lengthy string assigned to the button
is passed to AutoCAD and turned into the following AutoLISP code:
(progn
(setq tileRad (atof (get_tile "gp_trad")))
(setq tileSpace (atof (get_tile "gp_spac")))
(done_dialog)
(setq UserClick T)
)
This code does several things: It retrieves the current values from the tiles
whose key values are gp_trad (the tile radius) and gp_spac (the tile spacing
value). Then atof converts the number string into a real number. The dialog
is terminated with the done_dialog function, and a value of T, or true, is
assigned to the variable UserClick.
You’re done assigning actions to the buttons. The next thing to do is to put
it all in motion.
Starting the Dialog
The start_dialog function displays a dialog box and accepts user input. The
start_dialog function requires no arguments.
(start_dialog)
Control passes to users when you issue start_dialog. Users can make
choices within the dialog box, until they press the OK or Cancel buttons.
Unloading the Dialog
When a user presses the OK or Cancel button, you need to unload the dialog.
Like start_dialog, unload_dialog is another simple function.
(unload_dialog dcl_id)

Determining What to Do Next
If the user pressed OK, you must build a list containing the values set by the
user’s interaction with the dialog. This list is what gp:getDialogInput will
return to its calling function. If the user pressed Cancel, the function returns
nil:
(if UserClick ; User clicked Ok
;; Build the resulting data
(progn
(setq Result (list
(cons 42 tileRad)
(cons 43 TileSpace)
(cons 3 objectCreateMethod)
(cons 4 plineStyle)
)
)
)
)
Putting the Code Together
With the examples above, and a few additional lines, you have the code
needed to complete the gp:getDialogInput function.
To put gp:getDialogInput together
1 Open your copy of gp-io.lsp in a VLISP text editor window.
2 Delete the code in gp:getDialogInput (the defun gp:getDialogInput state-
ment and everything after it).
3 Enter the following defun statement as the first line of code in the
gp:getDialogInput function:
(defun gp:getDialogInput (pathWidth / dcl_id objectCreateMethod
plineStyle tilerad tilespace result UserClick
dialogLoaded dialogShow)
The function expects a single argument (pathwidth), and establishes a num-
ber of local variables.
4 Following the code you added in step 3, enter the sample code from each of
the following sections of this chapter:
s “Setting Up Dialog Values”
s “Loading the Dialog File”
s “Loading a Specific Dialog into Memory”
s “Initializing the Default Dialog Values”
s “Assigning Actions to Tiles”

NOTE Enter just the first code example from “Assigning Actions to Tiles,” not
the fragments in the explanations that follow. Those fragments just repeat pieces
of the example.
s “Starting the Dialog”
s “Unloading the Dialog”
s “Determining What to Do Next”
5 After the last line of code, add the following:
)
)
Result;
) ;_ end of defun
6 Format the code you entered by choosing Tools ® Format Code in Editor
from the VLISP menu.
Updating a Stubbed-Out Function
You have now revised the gp:getDialogInput function. Whenever you mod-
ify a stubbed-out function, you should always check a couple of things:
s Has the defun statement changed? That is, does the function still take the
same number of arguments?
s Does the function return something different?
In the case of gp:getDialogInput, the answer to both questions is yes. The
function now accepts the parameter of the path width (to set the default tile
size and spacing). And instead of returning T, which is the value the stubbed-
out version of the function returned, gp:getDialogInput now returns an
association list containing four new values.
Both changes affect the code that calls the function and the code that han-
dles the return values from the functions. Replace your previous version of
the C:GPath function in gpmain.lsp with the following code:
(defun C:GPath (/ gp_PathData gp_dialogResults)
(if (setq gp_dialogResults (gp:getDialogInput (cdr(assoc 40
gp_PathData))))

(progn
;; Now take the results of gp:getPointInput and append this
;; to the added information supplied by gp:getDialogInput.
(setq gp_PathData (append gp_PathData gp_DialogResults))
;; At this point, you have all the input from the user.
;; "pointer" in the variable called PolylineName.
) ;_ end of progn
) ;_ end of if
) ;_ end of if
) ;_ end of defun
Take a look at the boldface lines in the revision of the main C:GPath function.
There are two essential changes to make the program work correctly:
s When the gp:getDialogInput function is invoked, the path width is
passed to it. This is done by extracting the value associated with the
key 40 index of the gp_PathData association list.
s The association list returned by gp:getPointInput is assigned to a variable
called gp_dialogResults. If this variable has a value, its content needs to
be appended to the association list values already stored in gp_PathData.
There are additional changes in the code resulting from the replacement of
placeholders in the stubbed-out version. The easiest thing to do is copy this
code from the online tutorial and paste it into your file.
Providing a Choice of Boundary Line Type
One requirement specified for the garden path application was to allow users
to draw the boundary outline as either a lightweight polyline or an old-style
polyline. The first version of gp:drawOutline you wrote always used a light-
weight polyline to draw the boundary. Now that the dialog box interface is
ready to go, you can build in the option for drawing an old-style polyline as
well. To accomplish this, gp:drawOutline must determine what kind of
polyline to draw, and then it must draw it.
The necessary changes to gp:drawOutline are included in the following code
fragment. Make the modification from the gpdraw.lsp file indicated in bold:

Cleaning Up | 67
p4 (polar p3 (+ PathAngle (Degrees->Radians 180))
PathLength)
poly2Dpoints (apply 'append
)
poly3Dpoints (mapcar 'float (append p1 p2 p3 p4))
;; get the polyline style
plineStyle (strcase (cdr (assoc 4 BoundaryData)))
) ;_ end of setq
;; Add polyline to the model space using ActiveX automation
(setq pline (if (= plineStyle "LIGHT")
;; create a lightweight polyline
(vla-addLightweightPolyline
*ModelSpace* ; Global Definition for Model Space
(gp:list->variantArray poly2Dpoints) ;data conversion
;; or create an old-style polyline
(vla-addPolyline
*ModelSpace*
(gp:list->variantArray poly3Dpoints) ;data conversion
) ;_ end of vla-addPolyline
) ;_ end of if
) ;_ end of setq
Typing the changes into your code can be very tricky, as you not only need
to add code but also to delete some existing lines and rearrange others. It is
recommended you copy the entire setq statement from the online tutorial
and paste it into your code.
Cleaning Up
If you have not done so already, delete the following chunk of code from the
C:GPath function in gpmain.lsp:
(princ ">")
You had been using this code as a placeholder, but now that gp:drawOutline
is functioning, you no longer need it.

Running the Application
Before running your program, save all the files you changed, if you have not
already done so. You can choose File ® Save All from the VLISP menu, or use
the ALT+SHIFT+ S keyboard shortcut to save all your open files.
The next thing you must do is reload all the files in VLISP.
To load and run all the files in your application
1 If the project file you created earlier in this lesson is not already open, choose
Project ® Open Project from the VLISP menu, then enter the project file
name gpath; do not include the .prj extension. If VLISP does not find the
project file, press the Browse button and choose the file from the Open
Project dialog box. Click Open.
2 Press the Load Source Files button in the project window.
3 Enter the (C:GPath) command at the VLISP Console prompt to run the pro-
gram. If you have some debugging to do, try using the tools you learned in
Lessons 2 and 3. And remember, if all else fails, you can always copy the code
from the TutorialVisualLISPLesson4 directory.
Also, try drawing the path using both lightweight and old-style polylines.
After drawing the paths, use the AutoCAD list command to determine
whether or not your program is drawing the correct entity types.
In this lesson, you
s Modularized your code by dividing it among four files.
s Organized your code modules in a VLISP project.
s Learned to define a dialog box with Dialog Control Language (DCL).
s Added AutoLISP code to set up and handle input in the dialog box.
s Modified your code to provide users with a choice of boundary line type.
Now you have a program that draws a garden path boundary. In the next les-
son, you will add the tiles to the garden path. In the process, you will be
introduced to more VLISP program development tools.

In This Lesson
69
5
Drawing the Tiles
By the end of this lesson, your application will meet the
basic requirements stated in Lesson 1. You will add the
functionality for drawing tiles within the boundary of
the garden path and provide this function using several
different methods of entity creation. You will also learn
some keyboard shortcuts and new editing tools.
s Introducing More Visual LISP
Editing Tools
s Adding Tiles to the Garden Path
s Testing the Code

70 | Lesson 5 Drawing the Tiles
Introducing More Visual LISP Editing Tools
Open your copy of gpdraw.lsp in a VLISP text editor window, if the file is not
already open. There are a couple of things about this code that are typical of
much of the code you will be developing with VLISP. First, there are many
parentheses and parentheses within parentheses. Second, there are many
function calls, and some of those functions have very long names
(vla-addLightweightPolyline, for example). VLISP provides some editing
tools to help you deal with these common features of AutoLISP code.
Matching Parentheses
VLISP provides a parenthesis matching feature to help you find the close
parenthesis that corresponds to an open parenthesis.
To match an open parenthesis with its corresponding close parenthesis
1 Place your cursor in front of the opening parenthesis that precedes the setq
function call.
2 Press CTRL +SHIFT+]. (Double-clicking also does the trick.)
VLISP finds the closing parenthesis that matches the one you chose, and
selects all the code in between. Not only does this ensure you typed in the
correct number of parentheses, it also makes it easy to copy or cut the
selected text. This might have come in handy when you updated this call at
the end of Lesson 4.
Why else might you want to do this? You can copy a chunk of code to the
VLISP Console window, paste it there, and try it out. Or maybe you have fig-
ured out how to replace 50 lines of code with three really marvelous lines of
much better code. You can quickly select the old code using the parentheses
matching tool, then eliminate it with a single keystroke. It is a lot quicker to
let VLISP find an entire block than for you to hunt down every last closing
parenthesis.
There is a corresponding key command for matching and selecting back-
ward. To try this, put your cursor after a closing parenthesis, then either
double-click or press CTRL +SHIFT +[. VLISP searches for the corresponding
opening parenthesis, and selects it along with the enclosed code.
Both commands are also available by choosing Edit ® Parentheses Matching
from the VLISP menu.

Introducing More Visual LISP Editing Tools | 71
Completing a Word Automatically
Imagine you are adding some new functionality to your program using the
following code:
ObjectCreationStyle (strcase (cdr (assoc 3 BoundaryData)))
(if (equal ObjectCreationStyle "COMMAND")
(progn
(setq firstCenterPt(polar rowCenterPt (Degrees->Radians 45)
distanceOnPath))
(gp:Create_activeX_Circle)
)
)
(Don’t worry about what this code actually does, if anything. It is only an
example that includes several long variable and function names.)
VLISP can save you some keystrokes by completing words for you.
To use the Visual LISP Complete Word by Match feature
1 Scroll to the bottom of the gpdraw.lsp file and enter the following code:
(if (equal Ob
2 Press CTRL +SPACEBAR.
VLISP just saved you seventeen keystrokes as it searched within the current
file and found the closest match to the last two letters you typed.
3 Complete the line of code so that it looks like the following:
(if (equal ObjectCreationStyle "COMMAND")
4 Add the following lines:
(progn
(setq firstCenterPt(p
5 Press CTRL +SPACEBAR.
VLISP matches the most recent “p” word, which happens to be progn. How-
ever, the word you need is polar. If you keep pressing CTRL +SPACEBAR,
VLISP cycles through all the possible matches in your code. Eventually, it will
come around to polar.
6 Delete all the code you just entered; it was for demonstration purposes only.
The Complete Word by Match feature is also available from the VLISP Search
menu.

Completing a Word by Apropos
If you have worked with AutoLISP before, you may have had to type in an
expression similar to the one shown below:
(setq myEnt (ssname mySelectionSet ssIndex))
Often, it is confusing to keep track of all the selection set functions: ssname,
ssget, sslength, and so on. VLISP can help, using its Complete Word by
Apropos feature.
To use the Visual LISP Complete Word by Apropros feature
1 Scroll to the bottom of the gpdraw.lsp file and enter the following on a blank
line:
(setq myEnt (ent
2 Press CTRL +SHIFT+SPACEBAR.
VLISP displays a list of all AutoLISP symbols that begin with the letters ent.
Use the cursor keys (the up and down arrow keys) to move through the list.
Select ENTGET, then press ENTER.
VLISP replaces the ent you typed with ENTGET.
3 Delete the code.
Getting Help with a Function
The code that adds a lightweight polyline to the drawing calls a function
named vla-addLightweightPolyline. Not only is that a lengthy term to
write, but there are several functions whose names begin with vla-add that
you will use to create entities. Rather than consulting a manual to look up
the function name every time you create a program, let VLISP help.
To get help with using a function
1 Enter the following on a blank line:
(vla-add
2 Press CTRL +SHIFT+SPACEBAR.
3 Scroll through the list until you find vla-addLightweightPolyline.
4 Double-click on vla-addLightweightPolyline.
VLISP displays the Symbol Service dialog box for the selected function.
5 Press the Help button in the Symbol Service dialog box. (For ActiveX
functions, you will be directed to the ActiveX and VBA Reference.)

Adding Tiles to the Garden Path | 73
6 Delete the changes you made to gpdraw.lsp; these were for demonstration
purposes only. Also, close the Symbol Service and Apropos windows.
Adding Tiles to the Garden Path
You now have a path boundary and are ready to fill it with tiles. You will need
to apply some logic and work through a little geometry.
Applying Some Logic
One thing you need to do is determine how to space out the tiles and draw
them. If this were a simple rectilinear grid of tiles, you could use the
AutoCAD ARRAY command to fill in the tiles. But for the garden path, you
need to have each row of tiles offset from the previous row.
This row-offset pattern is a repeating pattern. Think of how you might go
about laying the tiles if you were building the actual path. You would prob-
ably be inclined to start at one end and just keep laying down rows until
there wasn’t any more space left.
SpaceToFill
SpaceFilled
OffsetFromCenter
RowSpacing

Here is the logic in pseudo-code:
At the starting point of the path
Figure out the initial row offset from center (either centered on
the path or offset by one "tile space").
While the space of the boundary filled is less than the space to
fill,
Draw a row of tiles.
Reset the next start point (incremented by one "tile space").
Add the distance filled by the new row to the amount of space
filled.
Toggle the offset (if it is centered, set it up off-center, or
vice versa).
Go back to the start of the loop.
Applying Some Geometry
There are only a few dimensions you need to know to draw the garden path.
The half width is easy: it is just half the width of the path. You already
defined the code to obtain this width from users and saved it in an associa-
tion list.
Tile spacing is also easy; it is twice the radius (that is, the diameter) plus the
space between the tiles. The dimensions are also obtained from users.
Row spacing is a little trickier, unless you are really sharp with trigonometry.
Here is the formula:
Row Spacing = (Tile Diameter + Space between Tiles) * (the sine
of 60 degrees)
Drawing the Rows
See if you can make sense of the following function. Compare it to the
pseudo-code and try to catch the geometric calculations just described. There
may be a few AutoLISP functions that are new to you. If you need help with
these functions, refer to the AutoLISP Reference. For now, just read the code;
do not write anything.
(defun gp:Calculate-and-Draw-Tiles (BoundaryData / PathLength
TileSpace TileRadius SpaceFilled SpaceToFill
RowSpacing offsetFromCenter
rowStartPoint pathWidth pathAngle
ObjectCreationStyle TileList)
(setq PathLength (cdr (assoc 41 BoundaryData))
TileSpace (cdr (assoc 43 BoundaryData))
TileRadius (cdr (assoc 42 BoundaryData))
SpaceToFill (- PathLength TileRadius)
RowSpacing (* (+ TileSpace (* TileRadius 2.0))
(sin (Degrees->Radians 60))
) ;_ end of *

SpaceFilled RowSpacing
offsetFromCenter 0.0
offsetDistance (/ (+ (* TileRadius 2.0) TileSpace) 2.0)
rowStartPoint (cdr (assoc 10 BoundaryData))
pathWidth (cdr (assoc 40 BoundaryData))
pathAngle (cdr (assoc 50 BoundaryData))
) ;_ end of setq
;; Compensate for the first call to gp:calculate-Draw-tile Row
;; in the loop below.
(setq rowStartPoint
(polar rowStartPoint
(+ pathAngle pi)
(/ TileRadius 2.0)
) ;_ end of polar
) ;_ end of setq
;; Draw each row of tiles.
(while (<= SpaceFilled SpaceToFill)
;; Get the list of tiles created, adding them to our list.
(setq tileList (append tileList
(gp:calculate-Draw-TileRow
(setq rowStartPoint
(polar rowStartPoint
pathAngle
RowSpacing
) ;_ end of polar
) ;_ end of setq
TileRadius
TileSpace
pathWidth
pathAngle
offsetFromCenter
ObjectCreationStyle
) ;_ end of gp:calculate-Draw-TileRow
) ;_ end of append
;; Calculate the distance along the path for the next row.
SpaceFilled (+ SpaceFilled RowSpacing)
;; Alternate between a zero and a positive offset
;; (causes alternate rows to be indented).
offsetFromCenter
(if (= offsetFromCenter 0.0)
offsetDistance
0.0
) ;_ end of if
) ;_ end of setq
) ;_ end of while
;; Return the list of tiles created.
tileList
) ;_ end of defun

A couple of sections from the code may need a little extra explanation.
The following code fragment occurs right before the while loop begins:
;; Compensate for the very first start point!!
(setq rowStartPoint(polar rowStartPoint
(+ pathAngle pi)(/ TileRadius 2.0)))
There are three pieces to the puzzle of figuring out the logic behind this
algorithm:
s The rowStartPoint variable starts its life within the
gp:Calculate-and-Draw-Tiles function by being assigned the point the
user selected as the start point of the path.
s The very first argument passed to the gp:calculate-Draw-TileRow func-
tion does the following:
(setq rowStartPoint(polar rowStartPoint pathAngle RowSpacing))
Another way of stating this is: At the time the
gp:calculate-Draw-TileRow function is called, the rowStartPoint
variable is set to one RowSpacing distance beyond the current
rowStartPoint.
s The rowStartPoint argument is used within gp:calculate-Draw-TileRow
as the starting point for the centers of the circles in the row.
To compensate for the initial forward shifting of the rowStartPoint during
the drawing of the first row (that is, the first cycle through the while loop),
you will want to shift rowStartPoint slightly in the opposite direction. The
aim is to avoid the appearance of a large margin of empty space between the
path boundary and the first row. Half the TileRadius is a sufficient amount
by which to move the point. This can be achieved by using polar to project
rowStartPoint along a vector oriented 180 degrees from the PathAngle. If
you think about it, this places the point temporarily outside the path
boundary.
The next fragment (modified for readability) may be a little puzzling:
(setq tileList (append tileList
(gp:calculate-Draw-TileRow
(setq rowStartPoint
(polar rowStartPoint pathAngle RowSpacing)
) ;_ end of setq
TileRadius TileSpace pathWidth pathAngle
offsetFromCenter ObjectCreationStyle
)))
In essence, there is setq wrapped around an append wrapped around the call
to gp:calculate-Draw-TileRow.

The gp:calculate-Draw-TileRow function will return the Object IDs for each
tile drawn. (The Object ID points to the tile object in the drawing.) You are
drawing the tiles row by row, so the function returns the Object IDs of one
row at a time. The append function adds the new Object IDs to any existing
Object IDs stored in tileList.
Near the end of the function, you can find the following code fragment:
(setq offsetFromCenter
(if (= offsetFromCenter 0.0)
offsetDistance
0.0
)
)
This is the offset toggle, which determines whether the row being drawn
should begin with a circle centered on the path or offset from the path. The
pseudo-code for this algorithm follows:
Set the offset amount to the following:
If the offset is currently zero, set it to the offset distance;
Otherwise, set it back to zero.
Drawing the Tiles in a Row
Now that you have the logic for drawing the path, the next step is to figure
out how to draw the tiles in each row. In the following diagram, there are two
cases shown: a row where the offset from the center of the path is equal to
0.0, and a case where the offset is not equal to zero. Take a look at the dia-
gram, then read the pseudo-code that follows.
Set up variables for StartPoint, angp90, angm90, and so on.
Set the variable FirstCenterPoint to the StartPoint + offset amount
(which may be 0.0).
Set the initial value of TileCenterPt to FirstCenterPoint.
HalfWidth
dist to TileCenterPt
FirstCenterPt
StartPt

(Comment: Begin by drawing the circles in the angp90 direction.)
While the distance from the StartPoint to the TileCenterPt is less
than the HalfWidth:
Draw a circle (adding to the accumulating list of circles).
Set TileCenterPt to the next tile space increment in the angp90
direction.
End While
Reset the TileCenterPoint to the FirstCenterPoint + the tile space
increment at angm90.
While the distance from the StartPoint to the TileCenterPt is less
than the HalfWidth:
Draw a circle (adding to the accumulating list of circles).
Set TileCenterPt to the next tile space increment in the angm90
direction.
End While
Return the list of circles.
Looking at the Code
Now look at the code for the gp:calculate-Draw-TileRow function:
(defun gp:calculate-Draw-TileRow (startPoint TileRadius
TileSpace pathWidth pathAngle offsetFromCenter
ObjectCreationStyle / HalfWidth TileDiameter
ObjectCreationFunction angp90 angm90
firstCenterPt TileCenterPt TileList)
(setq HalfWidth (- (/ pathWidth 2.00) TileRadius)
Tilespacing (+ (* TileRadius 2.0) TileSpace)
TileDiameter (* TileRadius 2.0)
firstCenterPt (polar startPoint angp90 offsetFromCenter)
tileCenterPt firstCenterPt
ObjectCreationStyle(strcase ObjectCreationStyle)
ObjectCreationFunction
(cond
((equal ObjectCreationStyle "ACTIVEX")
gp:Create_activeX_Circle
)
((equal ObjectCreationStyle "ENTMAKE")
gp:Create_entmake_Circle
)
((equal ObjectCreationStyle "COMMAND")
gp:Create_command_Circle
)

(T
(alert (strcat "ObjectCreationStyle in function
gp:calculate-Draw-TileRow"
"nis invalid. Contact developer for assistance."
"n ObjectCreationStyle set to ACTIVEX"
)
)
setq ObjectCreationStyle "ACTIVEX")
)
)
)
;; Draw the circles to the left of the center.
(while (< (distance startPoint tileCenterPt) HalfWidth)
;; Add each tile to the list to return.
(setq tileList
(cons
(ObjectCreationFunction tileCenterPt TileRadius)
tileList
)
)
;; Calculate the center point for the next tile.
(setq tileCenterPt
(polar tileCenterPt angp90 TileSpacing)
)
);_ end of while
;; Draw the circles to the right of the center.
(setq tileCenterPt
(polar firstCenterPt angm90 TileSpacing))
(while (< (distance startPoint tileCenterPt) HalfWidth)
;; Add each tile to the list to return.
(setq tileList
(cons
(ObjectCreationFunction tileCenterPt TileRadius)
tileList
)
)
;; Calculate the center point for the next tile.
(setq tileCenterPt (polar tileCenterPt angm90 TileSpacing))
);_ end of while
;; Return the list of tiles.
tileList
) ;_ end of defun

The AutoLISP code logic follows the pseudo-code, with the following
addition:
(setq ObjectCreationFunction
(cond
((equal ObjectCreationStyle "ACTIVEX")
gp:Create_activeX_Circle
)
((equal ObjectCreationStyle "ENTMAKE")
gp:Create_entmake_Circle
)
((equal ObjectCreationStyle "COMMAND")
gp:Create_command_Circle
)
(T
(alert
(strcat
"ObjectCreationStyle in function gp:calculate-Draw-TileRow"
"nis invalid. Contact the developer for assistance."
"n ObjectCreationStyle set to ACTIVEX"
) ;_ end of strcat
) ;_ end of alert
(setq ObjectCreationStyle "ACTIVEX")
)
) ;_ end of cond
) ;_ end of setq
Remember the specification to allow users to draw the tiles (circles) using
either ActiveX, the entmake function, or the command function? The
ObjectCreationFunction variable is assigned one of three functions,
depending on the ObjectCreationStyle parameter (passed from C:GPath
and through gp:Calculate-and-Draw-Tiles). Here are the three functions as
they will be defined in gpdraw.lsp:
(defun gp:Create_activeX_Circle (center radius)
(vla-addCircle *ModelSpace*
(vlax-3d-point center) ; convert to ActiveX-compatible 3D point
radius
)
) ;_ end of defun
(defun gp:Create_entmake_Circle(center radius)
(entmake
(list (cons 0 "CIRCLE") (cons 10 center) (cons 40 radius))
)
(vlax-ename->vla-object (entlast))
)
(defun gp:Create_command_Circle(center radius)
(command "_CIRCLE" center radius)
(vlax-ename->vla-object (entlast))
)
The first function draws a circle using an ActiveX function and returns an
ActiveX object.

Testing the Code | 81
The second function draws a circle using entmake. It returns an entity name
converted into an ActiveX object.
The third function draws a circle using command. It also returns an entity
name converted into an ActiveX object.
Testing the Code
If you’ve made it this far, you have earned a shortcut.
To test the code
1 Close all the active windows within VLISP, including any open project
windows.
2 Copy the entire contents of the TutorialVisualLISPLesson5 directory to your
MyPath tutorial directory.
3 Open the project file gpath5.prj using Select Project ® Open Project from the
VLISP menu bar.
4 Load the project source files.
5 Activate (switch to) the AutoCAD window and issue the gpath command to
run the program.
6 Run gpath to draw the garden path three times, each time using a different
entity creation method. Do you notice a difference in the speed with which
the path is drawn with each method?
You started this lesson by learning VLISP editing features that helped you
s Match the parentheses in your code.
s Find and complete a function name.
s Obtain online help for a function.
You finished the lesson by building code that draws the tiles in the garden
path. You now have a program that meets the requirements established at the
very beginning of this tutorial.
At this point, you probably have acquired enough experience with VLISP to
venture off on your own. But if you are up to it, there are two more lessons
in this tutorial that demonstrate the use of reactor functions and other
advanced features of the VLISP environment.

In This Lesson
83
6
Acting with Reactors
In this lesson, you will learn about reactors and how to
attach them to drawing events and entities. Reactors
allow your application to be notified by AutoCAD when
particular events occur. For example, if a user moves an
entity that your application has attached a reactor to,
your application will receive notification that the entity
has moved. You can program this to trigger additional
operations, such as moving other entities associated
with the one the user moved, or perhaps updating a text
tag that records revision information on the altered
drawing feature. In effect, it is like setting up your
application with a pager and telling AutoCAD to beep
the application when something happens.
s Reactor Basics
s Designing Reactors for the
Garden Path
s Test Driving Your Reactors

84 | Lesson 6 Acting with Reactors
Reactor Basics
A reactor is an object you attach to the drawing editor, or to specific entities
within a drawing. Extending the metaphor of the pager, the reactor object is
an automatic dialer that knows how to call your pager when something
significant happens. The pager within your application is an AutoLISP
function called by the reactor; such a function is known as a callback function.
NOTE The complexity of the application code and the level of expertise
required for these final two lessons is much higher than Lessons 1 through 5.
There is a great deal of information presented, but it is not all explained at the
same level of detail as in the previous lessons. If you are a beginner, don’t worry
if you don’t get it the first time. Consider this just a first taste of some of the very
powerful but more technically difficult features of VLISP.
Reactor Types
There are many types of AutoCAD reactors. Each reactor type responds to one
or more AutoCAD events. Reactors are grouped into the following categories:
Editor Reactors Notify your application each time an AutoCAD command
is invoked.
Linker Reactors Notify your application every time an ObjectARX
application is loaded or unloaded.
Database
Reactors
Correspond to specific entities or objects within a drawing
database.
Document
Reactors
Notify your application in MDI mode of a change to the
current drawing document, such as opening of a new
drawing document, activating a different document
window, and changing a document’s lock status.
Object
Reactors
Notify you each time a specific object is changed, copied,
or deleted.
With the exception of editor reactors, there is one type of reactor for each
reactor category. Editor reactors encompass a broad class of reactors: for
example, DXF™
reactors that notify an application when a DXF file is
imported or exported, and Mouse reactors that notify of mouse events such
as double-clicks.
Within the reactor categories, there are many specific events to which you
can attach a reactor. AutoCAD allows users to perform many different kinds

Designing Reactors for the Garden Path | 85
of actions, and it is up to you to determine the actions that you are interested
in. Once you have done this, you can attach your reactor “auto-dialer” to the
event, then write the callback function that is triggered when the event
occurs.
Designing Reactors for the Garden Path
To implement reactor functionality in the garden path application, start by
handling just a few events, rather than trying to cover all possible user
actions.
Selecting Reactor Events for the Garden Path
For the tutorial, set the following goals:
s When a corner point (vertex) of the garden path boundary is repositioned,
redraw the path so that the outline remains rectilinear. In addition, redraw
the tiles based on the new size and shape.
s When the garden path boundary is erased, erase the tiles as well.
Planning the Callback Functions
For each reactor event, you must plan the function that will be invoked when
the event occurs. The following pseudo-code outlines the logical sequence of
events that should occur when users drag one of the polyline vertices to a
new location:
Defun gp:outline-changed
Erase the tiles.
Determine how the boundary changed.
Straighten up the boundary.
Redraw new tiles.
End function
There is a complication, though. When the user begins dragging the outline
of a polyline vertex, AutoCAD notifies your application by issuing a
:vlr-modified event. However, at this point the user has just begun dragging
one of the polyline vertices. If you immediately invoke the
gp:outline-changed function, you will interrupt the action that the user is
in the midst of. You would not know where the new vertex location will be,
because the user has not yet selected its position. And finally, AutoCAD will
not allow your function to modify the polyline object while the user is still
dragging it. AutoCAD has the polyline object open for modification, and
leaves it open until the user finishes repositioning the object.

You need to change your approach. Here is the updated logic:
When the user begins repositioning a polyline vertex,
Invoke the gp:outline-changed function
Defun gp:outline-changed.
Set a global variable that stores a pointer to the polyline
being modified by the user.
End function
When the command completes,
Invoke the gp:command-ended function
Defun gp:command-ended.
Erase the tiles.
Get information on the previous polyline vertex locations.
Get information on the new polyline vertex locations.
Redefine the polyline (straighten it up).
Redraw the tiles.
End function
When a user completes modifying a path outline, AutoCAD notifies your
application by issuing a :vlr-commandEnded event, if you have established an
editor reactor.
The use of a global variable to identify the polyline the user changed is nec-
essary because there is no continuity between the gp:outline-changed and
gp:command-ended functions. In your application, both functions are
invoked and executed independently of one another. The global variable
stores important information set up in one function and accessed in the
other.
Now consider what to do if the user erases the garden path boundary. The
ultimate objective is to erase all the tiles. The following pseudo-code outlines
the logic:
When the user begins to erase the boundary,
Invoke the gp:outline-erased function
Defun gp:outline-erased.
Set a global variable that stores a pointer to the reactor
attached to the polyline currently being erased.
End function
When the erase is completed,
Invoke the gp:command-ended function
Defun gp:command-ended.
Erase the tiles that belonged to the now-deleted polyline.
End function
Planning for Multiple Reactors
Users may have several garden paths on the screen, and may be erasing more
than one. You need to plan for this possibility.
The reactor associated with an entity is an object reactor. If there are several
entities in the drawing, there may also be several object reactors, one for each

entity. A specific editing event, such as the erase command, can trigger
many callbacks, depending on how many of the selected entities have reac-
tors attached. Editor reactors, on the other hand, are singular in nature. Your
application should only attach a single :vlr-commandEnded event reactor.
The event sequence for both modifications—changing a vertex location and
erasing a polyline—ends up with actions that need to be performed within
the gp:command-ended function. Determine which set of actions to perform
for each condition. The following pseudo-code outlines the logic:
Defun gp:command-ended (2nd version)
Retrieve the pointer to the polyline (from a global variable).
Conditional:
If the polyline has been modified then:
Erase the tiles.
Get information on the previous polyline vertex locations.
Get information on the new polyline vertex locations.
Redefine the polyline (straighten it up).
Redraw the tiles.
End conditional expression.
If the polyline has been erased then:
Erase the tiles.
End conditional expression.
End Conditional
End function
Attaching the Reactors
The next step in planning a reactor-based application is to determine how
and when to attach reactors. You need to attach two object reactors for the
polyline border of any garden path (one to respond to a modification event,
the other to respond to erasure), and one editor reactor to alert your applica-
tion when users complete their modification to the polyline. Object reactors
are attached to entities, while editor reactors are registered with AutoCAD.
There is another consideration to account for. To recalculate the polyline out-
line—return it to a rectilinear shape—after the user modifies it, you must
know what the vertex configuration was before the modification. This infor-
mation cannot be determined once the polyline has been modified. By that
time you can only retrieve information on what the new configuration is. So
how do you solve this? You could keep this information in a global variable,
but there is a major problem with that idea. Users can draw as many garden
paths as they want, and every new path would require a new global variable.
This would get very messy.

Storing Data with a Reactor
You can solve the problem of saving the original configuration by taking
advantage of another feature of VLISP reactors—the ability to store data
within a reactor. When the user first draws a path boundary, you attach a
reactor to the boundary, along with the data you need to save. This entails
modifying your main program function, C:GPath, as follows:
Defun C:GPath
Do everything that is already done in the garden path
(and don't break anything).
Attach an object reactor to the polyline using these parameters:
A pointer to the polyline just drawn,
A list of data that you want the reactor to record,
A list of the specific polyline object events to be tracked,
along with the LISP callback functions to be invoked.
End of the object reactor setup.
Attach editor reactor to the drawing editor using the
following parameters:
Any data you want attached to the reactor (in this case,none)
A list of the specific editor reactor events to be tracked,
along with the LISP callback functions to be invoked.
End of the editor reactor setup.
End function
Updating the C:GPath Function
Update the C:GPath function by adding reactor creation logic.
To add reactor creation logic to C:GPath
1 Replace your version of gpmain.lsp with the updated version shown below.
Copy this code from the <AutoCAD directory>TutorialVisualLISPLesson6
directory:
(defun C:GPath (/
gp_PathData
gp_dialogResults
PolylineName
tileList
)
(setvar "OSMODE" 0) ;; Turn off object snaps.
;|
;; Lesson 6 adds a stubbed-out command reactor to AutoCAD.
;; However, it would be undesirable to react to every
;; drawing of a circle should the COMMAND tile creation
;; method be chosen by the user. So, disable the
;; *commandReactor* in case it exists.
|;

(if *commandReactor*
(progn
(setq *commandReactor* nil)
(vlr-remove-all :VLR-Command-Reactor)
)
)
(if (setq gp_dialogResults
(gp:getDialogInput
(cdr (assoc 40 gp_PathData))
) ;_ end of gp:getDialogInput
) ;_ end of setq
(progn
;; Now take the results of gp:getPointInput and append this to
;; the added information supplied by gp:getDialogInput.
(setq gp_PathData (append gp_PathData gp_DialogResults))
;; At this point, you have all the input from the user.
;; Draw the outline, storing the resulting polyline "pointer"
;; in the variable called PolylineName.
;; Next, it is time to draw the tiles within the boundary.
;; The gp_tileList contains a list of the object pointers for
;; the tiles. By counting up the number of points (using the
;; length function), we can print out the results of how many
;; tiles were drawn.
(princ "nThe path required ")
(princ
(length
(setq tileList (gp:Calculate-and-Draw-Tiles gp_PathData))
) ;_ end of length
) ;_ end of princ
(princ " tiles.")
;; Add the list of pointers to the tiles (returned by
;; gp:Calculate-and-Draw-Tiles) to gp_PathData. This will
;; be stored in the reactor data for the reactor attached
;; to the boundary polyline. With this data, the polyline
;; "knows" what tiles (circles) belong to it.
(setq gp_PathData
(append (list (cons 100 tileList))
; all the tiles
gp_PathData
) ;_ end of append
) ;_ end of setq

;; Before we attach reactor data to an object, let's look at
;; the function vlr-object-reactor.
;; vlr-object-reactor has the following arguments:
;; (vlr-object-reactor owner’s data callbacks)
;; The callbacks Argument is a list comprised
;; '(event_name . callback_function).
;;
;; For this exercise we will use all arguments
;; associated with vlr-object-reactor.
;; These reactor functions will execute only if
;; the polyline in PolylineName is modified or erased.
(vlr-object-reactor
;; The first argument for vlr-object-reactor is
;; the "Owner’s List" argument. This is where to
;; place the object to be associated with the
;; reactor. In this case, it is the vlaObject
;; stored in PolylineName.
(list PolylineName)
;; The second argument contains the data for the path
gp_PathData
;; The third argument is the list of specific reactor
;; types that we are interested in using.
'
(
;; reactor that is called upon modification of the object.
(:vlr-modified . gp:outline-changed)
;; reactor that is called upon erasure of the object.
(:vlr-erased . gp:outline-erased)
)
) ;_ end of vlr-object-reactor
;; Next, register a command reactor to adjust the polyline
;; when the changing command is finished.
(if (not *commandReactor*)
(setq *commandReactor*
(VLR-Command-Reactor
nil ; No data is associated with the command reactor
'(
(:vlr-commandWillStart . gp:command-will-start)
(:vlr-commandEnded . gp:command-ended)
)
) ;_ end of vlr-command-reactor
)
)

;; The following code removes all reactors when the drawing is
;; closed. This is extremely important!!!!!!!!!
;; Without this notification, AutoCAD may crash upon exiting!
(if (not *DrawingReactor*)
(setq *DrawingReactor*
(VLR-DWG-Reactor
nil ; No data is associated with the drawing reactor
'((:vlr-beginClose . gp:clean-all-reactors)
)
) ;_ end of vlr-DWG-reactor
)
)
) ;_ end of progn
) ;_ end of if
) ;_ end of if
) ;_ end of defun
;;; Display a message to let the user know the command name.
(princ "nType GPATH to draw a garden path.")
(princ)
2 Review the code modifications and comments describing what each new
statement does. This tutorial shows all modified code in boldface.
Adding Reactor Callback Functions
The reactor callback functions add a substantial amount of code to your
application. This code is provided for you in the Lesson6 directory.
To add the reactor callback functions to your program
1 Copy the gpreact.lsp file from the TutorialVisualLISPLesson6 directory to
your MyPath working directory.
2 Open the GPath project (if it is not already open), and press the Project
Properties button in the gpath project window.
3 Add the gpreact.lsp file to your project.
4 The gpreact.lsp file can reside anywhere in the order of files between utils.lsp,
which must remain first, and gpmain.lsp, which should remain as the last file.
Move any files, if necessary, then press OK.
5 Open the gpreact.lsp file by double-clicking on the file name within the gpath
project window.
Read through the comments in the file to help you understand what it is
doing. Note that all the callback functions are stubbed out; the only func-
tionality they perform is to display alert messages when they are fired.
The last function in the file is so important it deserves a heading of its own.

Cleaning Up After Your Reactors
Reactors are indeed very active. When you design an application that relies
on them, you could very well spend a great deal of time crashing your pro-
gram and possibly crashing AutoCAD as well. It helps to have a tool available
to remove all the reactors you have added, if necessary.
The gpreact.lsp file includes a function gp:clean-all-reactors that doesn’t
do much on its own. Instead, it makes a call to the CleanReactors function.
Add this function to your utils.lsp file by copying the following code to the
end of the file:
;;;--------------------------------------------------------------;
;;; Function: CleanReactors ;
;;;--------------------------------------------------------------;
;;; Description: General utility function used for cleaning up ;
;;; reactors. It can be used during debugging, as ;
;;; well as cleaning up any open reactors before ;
;;; a drawing is closed. ;
;;;--------------------------------------------------------------;
(defun CleanReactors ()
(mapcar 'vlr-remove-all
'(:VLR-AcDb-reactor
:VLR-Editor-reactor
:VLR-Linker-reactor
:VLR-Object-reactor
)
)
)
Test Driving Your Reactors
By now, you should have all the necessary pieces in place to use some live
reactors.
To test the reactor code
1 Load all the source code from your project. (Press the Load Source Files but-
ton in the gpath project window.)
2 Fire up the C:GPath function and give it a spin.
The program will draw a garden path for you, just as you were able to in
Lesson 5. You won’t see anything interesting at first.
3 Try the following actions after you draw the path:
s Move a polyline vertex. Pick the polyline and turn on its grips, then drag
a vertex to a new location.
s Stretch the polyline.

Test Driving Your Reactors | 93
s Move the polyline.
s Erase the polyline.
Examine the messages that appear. You are watching the behind-the-scenes
activities of a powerful capability.
(If your application is not working correctly and you do not want to take the
time to debug it right now, you can run the sample code provided in the
TutorialVisualLISPLesson6 directory. Use the Gpath6 project in that
directory.)
NOTE Because of the reactor behavior, you may notice that after testing a reac-
tor sequence in AutoCAD, you cannot return to VLISP by pressing ALT+TAB, or
by clicking to activate the VLISP window. If this happens, simply enter vlisp at
the AutoCAD Command prompt to return to VLISP.
Examining Reactor Behavior in Detail
With a stack of scrap paper, start tracing the reactor events within the appli-
cation. Here is an example of the kinds of things you should track:
Draw ten garden paths, then track the following Command/Object combina-
tions, selecting the polylines in succession:
s Erase / Polyline border (path 1).
s Erase / Circle within a polyline (path 2).
s Erase / Two polylines (paths 3 and 4).
s Move / Polyline border (path 5).
s Move / Circle within a polyline (path 6).
s Move / Two polylines and several circles (paths 7 and 8).
s Move Vertex (via grips) / Polyline border (path 9).
s Stretch / Polyline border (path 10).
Command: erase
Object: Polyline border
Reactor sequence
1. Type in erase command
2. Callback: GP:COMMAND-WILL-START
3. Select objects: pick a polyline
4. Hit Enter (object selection complete)
5. Callback: GP:OUTLINE-ERASED
6. Callback: GP:OUTLINE-CHANGED
7. Callback: GP:COMMAND-ENDED

This exercise will give you a good understanding of what is happening
behind the scenes. At any time throughout Lesson 7 when the reactor func-
tionality becomes confusing, refer to your “reactor-trace sheets.”
In this lesson, you were introduced to AutoCAD reactors and how to imple-
ment them using VLISP. You designed a plan for adding reactors to the
garden path application, and added some of the code your program will need
to implement the plan.
You have now been through some very new and exciting stuff, from the
AutoLISP perspective. Reactors can add a great deal of functionality to an
application, but remember—the more powerful your programs can be, the
harder they can crash.
Another thing to keep in mind is that the way your application is designed,
the reactor functionality is not persistent from one drawing session to the
next. If you save a drawing that contains a garden path hooked up to reac-
tors, the reactors will not be there the next time you open the drawing. You
can learn about adding persistent reactors by reviewing the “Transient versus
Persistent Reactors” topic in the Visual LISP Developer’s Guide, and then read-
ing about the referenced functions in the AutoLISP Reference.

In This Lesson
95
7
Putting It All Together
In Lesson 6, you learned the basic mechanics behind
reactor-based applications. In Lesson 7, you will add
functionality to this knowledge and create a garden
path that knows how and when to modify itself. After
testing your application and determining that it works
satisfactorily, you will create a VLISP application from
your VLISP project.
You should consider this part of the tutorial as the
advanced topics section. If you are a beginner, you may
not understand all the AutoLISP code presented here.
There are several AutoLISP books listed at the end of this
lesson that provide more thorough information on
some of the advanced AutoLISP concepts presented
here.
s Planning the Overall Reactor
Process
s Adding the New Reactor
Functionality
s Redefining the Polyline
Boundary
s Wrapping Up the Code
s Building an Application
s Wrapping Up the Tutorial
s LISP and AutoLISP Books

96 | Lesson 7 Putting It All Together
Planning the Overall Reactor Process
You need to define several new functions in this lesson. Rather than present
you with details on all aspects of the new code, this lesson presents an over-
view and points out the concepts behind the code. At the end of the lesson,
you will have all the source code necessary to create a garden path applica-
tion identical to the sample program you ran in Lesson 1.
NOTE When you are in the midst of developing and debugging reactor-based
applications, there is always the potential of leaving AutoCAD in an unstable
state. This can be caused by several situations, such as failing to remove a reactor
from deleted entities. For this reason, it is recommended that before beginning
Lesson 7, you should close VLISP, save any open files as you do so, exit AutoCAD,
then restart both applications.
Begin by loading the project as it existed at the end of Lesson 6.
Two obvious pieces of work remain to be done in the garden path
application:
s Writing the object reactor callbacks.
s Writing the editor reactor callbacks.
You also need to consider how to handle the global variables in your pro-
gram. Often, it is desirable to have globals retain a value throughout an
AutoCAD drawing session. In the case of reactors, however, this is not the
case. To illustrate this, imagine a user of your garden path application has
drawn several garden paths in a single drawing. After doing this, the user
erases them, first one at a time, then two at a time, and so on, until all but
one path is erased.
Lesson 5 introduced a global variable *reactorsToRemove*, responsible for
storing pointers to the reactors for the polylines about to be erased. When
*reactorsToRemove* is declared in gp:outline-erased, the event lets you
know the polyline is about to be erased. The polyline is not actually removed
until the gp:command-ended event fires.
The first time the user deletes a polyline, things work just as you would
expect. In gp:outline-erased, you store a pointer to the reactor. When
gp:command-ended fires, you remove the tiles associated with the polyline to
which the reactor is attached, and all is well. Then, the user decides to erase
two paths. As a result, your application will get two calls to
gp:outline-erased, one for each polyline about to be erased. There are two
potential problems you must anticipate:

Planning the Overall Reactor Process | 97
s When you setq the *reactorsToRemove* variable, you must add a pointer
to a reactor to the global, making sure not to overwrite any values already
stored there. This means *reactorsToRemove* must be a list structure, so
you can append reactor pointers to it. You can then accumulate several
reactor pointers corresponding to the number of paths the user is erasing
within a single erase command.
s Every time gp:command-will-start fires, indicating a new command
sequence is beginning, you should reinitialize the *reactorsToRemove*
variable to nil. This is necessary so that the global is not storing reactor
pointers from the previous erase command.
If you do not reinitialize the global variable or use the correct data struc-
ture (in this case, a list), you will get unexpected behavior. In the case of
reactors, unexpected behavior can be fatal to your AutoCAD session.
Here is the chain of events that needs to occur for users to erase two garden
paths with a single erase command. Note how global variables are handled:
s Initiate the erase command. This triggers the gp:command-will-start
function. Set *reactorsToRemove* to nil.
s Select two polylines; your application is not yet notified.
s Press ENTER to erase the two selected polylines.
Your application gets a callback to gp:outline-erased for one of the
polylines. Add its reactor pointer to the null global, *reactorsToRemove*.
Your application gets a callback to gp:outline-erased for the second of
the polylines. Append its reactor pointer to the *reactorsToRemove* glo-
bal that already contains the first reactor pointer.
s AutoCAD deletes the polylines.
s Your callback function gp:command-ended fires. Eliminate any tiles associ-
ated with the reactor pointers stored in *reactorsToRemove*.
In addition to the *reactorsToRemove* global, your application also includes
a *polyToChange* global, which stores a pointer to any polyline that will be
modified. Two additional globals for the application will be introduced later
in this lesson.
Reacting to More User-Invoked Commands
When writing a reactor-based application, you need to handle any command
that affects your objects in a significant way. One of your program design
activities should be to review all possible AutoCAD editing commands and
determine how your application should respond to each one. The format of
the reactor-trace sheet shown near the end of Lesson 6 is very good for this
purpose. Invoke the commands you expect your user to use, and write down

the kind of behavior with which your application should respond. Other
actions to plan for include
s Determine what to do when users issue UNDO and REDO commands.
s Determine what to do when users issue the OOPS command after erasing
entities linked with reactors.
To prevent a very complex subject from becoming very, very complex, the
tutorial does not try to cover all the possibilities that should be covered, and
the functionality within this lesson is kept to an absolute minimum.
Even though you won’t be building in the complete functionality for these
extra commands, examine what a few additional editing functions would
require you to do:
s If users stretch a polyline boundary (using the STRETCH command) several
things should happen. It could be stretched in any direction, not just on
the major or minor axis, so the boundary may end up in a very odd shape.
In addition, you need to take into consideration how many vertices have
been stretched. A situation where only one vertex is stretched will result
in a polyline quite different from one in which two vertices are moved. In
any case, the tiles must be erased and new positions recalculated once you
determine the adjustments needed to the boundary.
s If users move a polyline boundary, all the tiles should be erased, then
redrawn in the new location. This is a fairly simple operation, because the
polyline boundary did not change its size or shape.
s If users scale a polyline boundary, you need to make a decision. Should the
tiles be scaled up as well, so that the path contains the same number of
tiles? Or, should the tile size remain the same and the application add or
remove tiles, depending on whether the polyline was scaled up or down?
s If users rotate a polyline boundary, all the tiles should be erased, then
redrawn in the new orientation.
To begin, though, just plan for the following:
s Warn the user upon command-start that the selected edit command (such
as stretch, move, or rotate) will have detrimental effects on a garden
path.
s If the user proceeds, erase the tiles and do not redraw them.
s Remove the reactors from the path outline.

NOTE In addition to user-invoked AutoCAD commands, entities may also be
modified or deleted through AutoLISP or ObjectARX applications. The example
provided in the Garden Path tutorial does not cover programmatic manipulation
of the garden path polyline boundary, such as through (entdel <polyline
entity>). In this case, the editor reactor events :vlr-commandWillStart and
:vlr-commandEnded will not be triggered.
Storing Information within the Reactor Objects
One other important aspect of the application you need to think about is
what kind of information to attach to the object reactor that is created for
each polyline entity. In Lesson 6, you added code that attached the contents
of gp_PathData (the association list) to the reactor. You expanded the data
carried within gp_PathData by adding a new keyed field (100) to the associ-
ation list. This new sublist is a list of pointers to all the circle entities assigned
to a polyline boundary.
Because of the work that needs to be done to recalculate the polyline bound-
ary, four additional key values should be added to gp_pathData:
;;; StartingPoint ;
;;; (12 . BottomStartingPoint) 15------------------------14 ;
;;; (15 . TopStartingPoint) | | ;
;;; EndingPoint 10 ----pathAngle---> 11 ;
;;; (13 . BottomEndingPoint) | | ;
;;; (14 . TopEndingPoint) 12------------------------13 ;
;;; ;
These ordered points are necessary to recalculate the polyline boundary
whenever the user drags a corner grip to a new location. This information
already exists within the gp:drawOutline function in gpdraw.lsp. But look at
the return value of the function. Currently, only the pointer to the polyline
object is returned. So you need to do three things:
s Assemble the perimeter points in the format required.
s Modify the function so that it returns the perimeter point lists and the
pointer to the polyline.
s Modify the C:GPath function so that it correctly deals with the newformat
of the values returned from gp:drawOutline.

Assembling the perimeter point lists is simple. Look at the code in
gp:drawOutline. The local variable p1 corresponds to the key value 12,
p2 to 13, p3 to 14, and p4 to 15. You can add the following function call to
assemble this information:
(setq polyPoints(list
(cons 12 p1)
(cons 13 p2)
(cons 14 p3)
(cons 15 p4)
))
Modifying the function so that it returns the polyline perimeter points and
the polyline pointer is also easy. As the last expression within
gp:drawOutline, assemble a list of the two items of information you want to
return.
(list pline polyPoints)
To add program logic to save the polyline perimeter points
1 Modify gp:drawOutline by making the changes shown in boldface in the fol-
lowing code (don’t overlook the addition of the polyPoints local variable to
the defun statement):
(defun gp:drawOutline (BoundaryData / PathAngle
Width HalfWidth StartPt PathLength
angm90 angp90 p1 p2
p3 p4 poly2Dpoints
poly3Dpoints plineStyle pline
polyPoints
)
;; extract the values from the list BoundaryData.
p4 (polar p3 (+ PathAngle
(Degrees->Radians 180)) PathLength)
poly2Dpoints (apply 'append
)
poly3Dpoints (mapcar 'float (append p1 p2 p3 p4))
;; get the polyline style.

plineStyle (strcase (cdr (assoc 4 BoundaryData)))
pline (if (= plineStyle "LIGHT")
;; create a lightweight polyline.
(vla-addLightweightPolyline
*ModelSpace* ; Global Definition for Model Space
(gp:list->variantArray poly2Dpoints)
;data conversion
;; or create a regular polyline.
(vla-addPolyline
*ModelSpace*
(gp:list->variantArray poly3Dpoints)
;data conversion
) ;_ end of vla-addPolyline
) ;_ end of if
polyPoints (list
(cons 12 p1)
(cons 13 p2)
(cons 14 p3)
(cons 15 p4)
)
) ;_ end of setq
(list pline polyPoints)
) ;_ end of defun
2 Modify the C:GPath function (in gpmain.lsp). Look for the line of code that
currently looks like this:
Change it so it appears as follows:
(setq PolylineList (gp:drawOutline gp_PathData)
PolylineName (car PolylineList)
gp_pathData (append gp_pathData (cadr PolylineList))
) ;_ end of setq
The gp_PathData variable now carries all the information required by the
reactor function.
3 Add PolylineList to the local variables section of the C:GPath function
definition.

Adding the New Reactor Functionality
In Lesson 6, you hooked up callback function gp:command-will-start to the
reactor event :vlr-commandWillStart. As it currently exists, the function dis-
plays some messages and initializes two global variables, *polyToChange*
and *reactorsToRemove*, to nil.
To add functionality to the gp:command-will-start callback function
1 Open your gpreact.lsp file.
2 In the gp:command-will-start function, add two variables to the setq func-
tion call by modifying it as follows:
;; Reset all four reactor globals to nil.
(setq *lostAssociativity* nil
*polyToChange* nil
*reactorsToChange* nil
*reactorsToRemove* nil)
3 Replace the remaining code in gp:command-will-start, up to the last princ
function call, with the following code:
(if (member (setq currentCommandName (car command-list))
'( "U" "UNDO" "STRETCH" "MOVE"
"ROTATE" "SCALE" "BREAK" "GRIP_MOVE"
"GRIP_ROTATE" "GRIP_SCALE" "GRIP_MIRROR")
) ;_ end of member
(progn
(setq *lostAssociativity* T)
(princ "nNOTE: The ")
(princ currentCommandName)
(princ " command will break a path's associativity .")
) ;_ end of progn
) ;_ end of if
This code checks to see if the user issued a command that breaks the associa-
tivity between the tiles and the path. If the user issued such a command, the
program sets the *lostAssociativity* global variable and warns the user.
As you experiment with the garden path application, you may discover addi-
tional editing commands that can modify the garden path and cause the loss
of associativity. Add these commands to the quoted list so that the user is
aware of what will happen. When this function fires, the user has started a
command but has not selected any entities to modify. The user could still
cancel the command, leaving things unchanged.

Adding the New Reactor Functionality | 103
Adding Activity to the Object Reactor Callback
Functions
In Lesson 6, you registered two callback functions with object reactor events.
The gp:outline-erased function was associated with the :vlr-erased reac-
tor event, and gp:outline-changed was associated with the :vlr-modified
event. You need to make these functions do what they are intended to do.
To make the object reactor callback functions do what they are intended to do
1 In gpreact.lsp, change gp:outline-erased so it appears as follows:
(defun gp:outline-erased (outlinePoly reactor parameterList)
(setq *reactorsToRemove*
(cons reactor *reactorsToRemove*))
(princ)
) ;_ end of defun
There is just one operation performed here. The reactor attached to the
polyline is saved to a list of all reactors that need to be removed. (Remember:
though reactors are attached to entities, they are separate objects entirely,
and their relationships to entities need to be managed just as carefully as reg-
ular AutoCAD entities.)
2 Change gp:outline-changed to reflect the following code:
(defun gp:outline-changed (outlinePoly reactor parameterList)
(if *lostAssociativity*
(setq *reactorsToRemove*
(cons reactor *reactorsToRemove*))
(setq *polytochange* outlinePoly
*reactorsToChange* (cons reactor *reactorsToChange*))
)
(princ)
)
There are two categories of functions that can modify the polyline outline.
The first category contains those commands that will break the path’s
associativity with its tiles. You checked for this condition in
gp:command-will-start and set the *lostAssociativity* global variable
accordingly. In this case, the tiles need to be erased, and the path is then in
the user’s hands. The other category is the grip mode of the STRETCH
command, where associativity is retained and you need to straighten out the
outline after the user has finished dragging a vertex to a new location.
The *polyToChange* variable stores a VLA-Object pointer to the polyline
itself. This will be used in the gp:command-ended function when it comes
time to recalculate the polyline border.

Designing the gp:command-ended Callback
Function
The gp:command-ended editor reactor callback function is where most action
takes place. Until this function is called, the garden path border polylines are
“open for modify;” that is, users may still be manipulating the borders in
AutoCAD. Within the reactor sequence, you have to wait until AutoCAD has
done its part of the work before you are free to do what you want to do.
The following pseudo-code illustrates the logic of the gp:command-ended
function:
Determine the condition of the polyline.
CONDITION 1 - POLYLINE ERASED (Erase command)
Erase the tiles.
CONDITION 2 - LOST ASSOCIATIVITY (Move, Rotate, etc.)
Erase the tiles.
CONDITION 3 - GRIP_STRETCH - REDRAW AND RE-TILE
Erase the tiles.
Get the current boundary data from the polyline.
If it is a lightweight polyline,
Process boundary data as 2D
Else
Process boundary data as 3D
End if
Redefine the polyline border (pass in parameters of the current
boundary configuration, as well as the old).
Get the new boundary information and put it into the format
required for setting back into the polyline entity.
Regenerate the polyline.
Redraw the tiles (force ActiveX drawing).
Put the revised boundary information back into the reactor
named in *reactorsToChange*.
End function
The pseudo-code is relatively straightforward, but there are several important
details buried in the pseudo-code, and they are things you would not be
expected to know at this point.
Handling Multiple Entity Types
The first detail is that your application may draw two kinds of polylines: old-
style and lightweight. These different polyline types return their entity data
in different formats. The old-style polyline returns a list of twelve reals: four
sets of X, Y, and Z points. The lightweight polyline, though, returns a list
eight reals: four sets of X and Y points.

You need to do some calculations to determine the revised polyline boundary
after a user moves one of the vertices. It will be a lot easier to do the calcula-
tions if the polyline data has a consistent format.
The Lesson 7 version of the utils.lsp file contains functions to perform the
necessary format conversions: xyzList->ListOfPoints extracts and formats
3D point lists into a list of lists, and xyList->ListOfPoints extracts and for-
mats 2D point lists into a list of lists.
To add the code for converting polyline data into a consistent format
1 If you have a copy of utils.lsp open in a VLISP text editor window, close it.
2 Copy the version of utils.lsp from the TutorialVisualLISPLesson7 directory
into your working directory.
In addition to the two functions that reformat polyline data, utils.lsp con-
tains additional utility functions needed in handling user alterations to the
garden path.
3 Open utils.lsp in a VLISP text editor window and review the new code.
Using ActiveX Methods in Reactor Callback
Functions
The second detail appearing in the pseudo-code shows up near the end, at
the step for redrawing the tiles. Here is the pseudo-code statement:
Redraw the tiles (force ActiveX drawing)
The parenthetical phrase says it all: force ActiveX drawing. Why is this
required? Why can’t the application use the object creation preference stored
in the association sublist?
The answer is you cannot use the command function for entity creation within
a reactor callback function. This has to do with some internal workings of
AutoCAD. You need to force the tile drawing routine to use ActiveX. You will
hear more about this issue later in this lesson.
Handling Nonlinear Reactor Sequences
The final important detail deals with a quirk in the command/reactor
sequence in AutoCAD when users modify a polyline by using the specialized
GRIP commands. These commands, such as GRIP_MOVE and GRIP_ROTATE,
are available from a shortcut menu after you select the grip of an object and
right-click. The reactor sequence is not as linear as a simple MOVE or ERASE
command. In effect, the user is changing to a different command while in
the midst of another. To demonstrate this situation, you can load the code

from Lesson 6 that traces the sequence of reactor events. Or simply review
the following annotated VLISP Console window output to see what happens:
;; To start, select the polyline and some of the circles by using a
;; crossing selection box. The items in the selection set--
;; the chosen circles and the polyline--are now shown with grips on.
;; To initiate the sequence, click on one of the polyline grips:
(GP:COMMAND-WILL-START #<VLR-Command-reactor> (GRIP_STRETCH))
;; Now change the command to a move by right-clicking and choosing
;; MOVE from the pop-up menu. Notice that the command-ended
;; reactor fires in order to close out the GRIP_STRETCH command
;; without having fired an object reactor event:
(GP:COMMAND-ENDED #<VLR-Command-reactor> (GRIP_STRETCH))
(GP:COMMAND-WILL-START #<VLR-Command-reactor> (GRIP_MOVE))
;; Now drag the outline (and the selected circles) to a new location.
(GP:OUTLINE-CHANGED #<VLA-OBJECT IAcadLWPolyline 028f3188>
#<VLR-Object-reactor> nil)
(GP:COMMAND-ENDED #<VLR-Command-reactor> (GRIP_MOVE))
This demonstrates that you cannot be certain your object reactor callbacks
will be called in all cases.
There is a related quirk in this sequence. Even during the final
command-ended callback, the circles that are still part of the grip selection
set cannot be deleted. These circles are still open by AutoCAD. If you attempt
to erase them during the command-ended callback, you can crash AutoCAD.
To get around this, you can use another global variable to store a list of point-
ers to the tile objects until they can be deleted.
To process nonlinear reactor sequences
1 Add the following function to the gpreact.lsp file:
(defun gp:erase-tiles (reactor / reactorData tiles tile)
(if (setq reactorData (vlr-data reactor))
(progn
;; Tiles in the path are stored as data in the reactor.
(setq tiles (cdr (assoc 100 reactorData)))
;; Erase all the existing tiles in the path.
(foreach tile tiles
(if (and (null (member tile *Safe-to-Delete*))
(not (vlax-erased-p tile))
)
(progn
(vla-put-visible tile 0)
(setq *Safe-to-Delete* (cons tile *Safe-to-Delete*))
)
)
)
(vlr-data-set reactor nil)
)
)
)

This new function will be used in the first phase of erasing tiles. Notice that
the tiles are not actually erased: they are made invisible and are added to a
global variable named *Safe-to-Delete*.
2 Add the following function to the gpreact.lsp file:
(defun Gp:Safe-Delete (activeCommand)
(if (not (equal
(strcase (substr activeCommand 1 5))
"GRIP_"
)
)
(progn
(if *Safe-to-Delete*
(foreach Item *Safe-to-Delete*
(if (not (vlax-erased-p Item))
(vla-erase item)
)
)
)
(setq *Safe-to-Delete* nil)
)
)
)
This function can be invoked at a time when a GRIP_MOVE or GRIP_STRETCH
command is not being executed.
Coding the command-ended Function
Now that you have seen the pseudo-code and handled some important
details, replace the stubbed-out code in the gp:command-ended reactor call-
back with the following:
(defun gp:command-ended (reactor command-list
/ objReactor
reactorToChange reactorData
coordinateValues currentPoints
newReactorData newPts
tileList
)
(cond
;; CONDITION 1 - POLYLINE ERASED (Erase command)
;; If one or more polyline borders are being erased (indicated
;; by the presence of *reactorsToRemove*), erase the tiles
;; within the border, then remove the reactor.
(*reactorsToRemove*
(foreach objReactor *reactorsToRemove*
(gp:erase-tiles objReactor)
)
(setq *reactorsToRemove* nil)
)

;; CONDITION 2 - LOST ASSOCIATIVITY (Move, Rotate, etc.)
;; If associativity has been lost (undo, move, etc.), then
;; erase the tiles within each border
;;
((and *lostassociativity* *reactorsToChange*)
(foreach reactorToChange *reactorsToChange*
(gp:erase-tiles reactorToChange)
)
(setq *reactorsToChange* nil)
)
;; CONDITION 3 - GRIP_STRETCH
;; In this case, the associativity of the tiles to the path is
;; kept, but the path and the tiles will need to be
;; recalculated and redrawn. A GRIP_STRETCH can only be
;; performed on a single POLYLINE at a time.
((and (not *lostassociativity*)
*polytochange*
*reactorsToChange*
(member "GRIP_STRETCH" command-list)
;; for a GRIP_STRETCH, there will be only one reactor in
;; the global *reactorsToChange*.
(setq reactorData
(vlr-data (setq reactorToChange
(car *reactorsToChange*)
)
)
)
)
;; First, erase the tiles within the polyline border.
(gp:erase-tiles reactorToChange)
;; Next, get the current coordinate values of the polyline
;; vertices.
(setq coordinateValues
(vlax-safearray->list
(vlax-variant-value
(vla-get-coordinates *polyToChange*)
)
)
)
;; If the outline is a lightweight polyline, you have
;; 2d points, so use utility function xyList->ListOfPoints
;; to convert the coordinate data into lists of
;; ((x y) (x y) ...) points. Otherwise, use the
;; xyzList->ListOfPoints function that deals
;; with 3d points, and converts the coordinate data into
;; lists of ((x y z) (x y z) ... ) points.
(setq CurrentPoints
(if (= (vla-get-ObjectName *polytochange*) "AcDbPolyline")
(xyList->ListOfPoints coordinateValues)
(xyzList->ListOfPoints coordinateValues)
)
)

;; Send this new information to RedefinePolyBorder -- this
;; will return the new Polyline Border
(setq NewReactorData
(gp:RedefinePolyBorder CurrentPoints reactorData)
)
;; Get all the border Points and ...
(setq newpts (list (cdr (assoc 12 NewReactorData))
(cdr (assoc 13 NewReactorData))
)
)
;; ...update the outline of the polyline with the new points
;; calculated above. If dealing with a lightweight polyline,
;; convert these points to 2D (since all the points in
;; newpts are 3D), otherwise leave them alone.
(if (= (cdr (assoc 4 NewReactorData)) "LIGHT")
(setq newpts (mapcar '(lambda (point)
(3dPoint->2dPoint Point)
)
newpts
)
)
)
;; Now update the polyline with the correct points.
(vla-put-coordinates
*polytochange*
;; For description of the list->variantArray see utils.lsp.
(gp:list->variantArray (apply 'append newpts))
)
;; Now use the current definition of the NewReactorData,
;; which is really the same as the garden path data
;; structure. The only exception is that the field (100)
;; containing the list of tiles is nil. This is OK since
;; gp:Calculate-and-Draw-Tiles does not require this field
;; to draw the tiles. In fact this function creates the tiles
;; and returns a list of drawn tiles.
(setq tileList (gp:Calculate-and-Draw-Tiles
;; path data list without correct tile list
NewReactorData
;; Object creation function
;; Within a reactor this *MUST* be ActiveX
"ActiveX"
)
)

;; Now that you have received all the tiles drawn, rebuild
;; the data structure with the correct tileList value and
;; reset the data property in the reactor.
;; Update the tiles associated with the polyline border.
(subst (cons 100 tileList)
(assoc 100 NewReactorData)
NewReactorData
)
)
;; By now you have the new data associated with the polyline.
;; All there is left to do is associate it with the reactor
;; using vlr-data-set.
(vlr-data-set (car *reactorsToChange*) NewReactorData)
;; Remove all references to the temporary
;; variables *polytochange* and *reactorsToChange*.
(setq *polytochange* nil
*reactorsToChange* nil
)
)
)
;; Delete any items in the *Safe-to-Delete* global if you can!!!
(Gp:Safe-Delete (car command-list))
(princ)
)
Updating gp:Calculate-and-Draw-Tiles
Earlier in this lesson, it was noted that you need to force
gp:Calculate-and-Draw-Tiles to use ActiveX to create objects when
invoked from a reactor callback. This means overriding the object creation
style (ActiveX, entmake, or command) chosen by the user, if necessary. The
code you just updated, in the gp:command-ended function, contains the
following invocation of the tile drawing routine:
(setq tileList (gp:Calculate-and-Draw-Tiles
;; path data list without correct tile list.
NewReactorData
;; Object creation function.
;; Within a reactor this *MUST* be ActiveX.
"ActiveX"
)
)
Two parameters are passed to gp:Calculate-and-Draw-Tiles:
NewReactorData (which is a list in the form of the original gp_PathData
association list) and the string "ActiveX" (which will set the object creation
style). But take a look at the current definition of

gp:Calculate-and-Draw-Tiles. (In case you have forgotten, this function is
defined in gpdraw.lsp.) Here is the part of the function that declares the
parameters and local variables:
(defun gp:Calculate-and-Draw-Tiles (BoundaryData /
PathLength TileSpace
TileRadius SpaceFilled
SpaceToFill RowSpacing
offsetFromCenter rowStartPoint
pathWidth pathAngle
ObjectCreationStyle TileList)
Notice only that one parameter is currently specified, and
ObjectCreationStyle is identified as a local variable. Review how the
ObjectCreationStyle variable is set, which is a little farther into the func-
tion:
(setq ObjectCreationStyle (strcase (cdr (assoc 3 BoundaryData))))
The ObjectCreationStyle is currently set internally within the function by
retrieving the value tucked away in the BoundaryData variable (the associa-
tion list). But now you need to be able to override that value.
To modify gp:Calculate-and-Draw-Tiles to accept an object creation style
argument
1 Add the ObjectCreationStyle variable to the function argument.
2 Remove ObjectCreationStyle from the local variables.
The defun statement for the function should look like the following:
(defun gp:Calculate-and-Draw-Tiles (BoundaryData
ObjectCreationStyle
/ PathLength TileSpace
TileRadius SpaceFilled
SpaceToFile RowSpacing
offsetFromCenter rowStartPoint
pathWidth pathAngle
TileList) ; remove ObjectCreationStyle from locals
Note that if you declare a variable both as a parameter (before the slash) and
as a local variable (after the slash), VLISP will point this out to you. For
example, if you declare ObjectCreationStyle as both a parameter and a
variable, then use the VLISP syntax checking tool on the
gp:Calculate-and-Draw-Tiles function, the following message will appear
in the Build Output window:
; *** WARNING: same symbol before and after / in arguments list:
OBJECTCREATIONSTYLE

3 Modify the first setq expression within gp:Calculate-and-Draw-Tiles so
that it looks like the following (changes indicated in bold):
(setq
TileSpace (cdr (assoc 43 BoundaryData))
TileRadius (cdr (assoc 42 BoundaryData))
SpaceToFill (- PathLength TileRadius)
RowSpacing (* (+ TileSpace (* TileRadius 2.0))
(sin (Degrees->Radians 60))
)
SpaceFilled RowSpacing
offsetFromCenter 0.0
offsetDistance /(+(* TileRadius 2.0)TileSpace)2.0)
rowStartPoint cdr (assoc 10 BoundaryData))
pathWidth cdr (assoc 40 BoundaryData))
pathAngle cdr (assoc 50 BoundaryData))
) ;_ end of setq
(if (not ObjectCreationStyle)
(setq ObjectCreationStyle (strcase (cdr (assoc 3 BoundaryData))))
)
The original assignment statement for ObjectCreationStyle has been
removed. The code now checks to see if a value has been provided for
ObjectCreationStyle. If ObjectCreationStyle is not set (that is, the value is
nil), the function assigns it a value from the BoundaryData variable.
There is one more series of changes you need to make to
gp:Calculate-and-Draw-Tiles.
Modifying Other Calls to gp:Calculate-and-Draw-
Tiles
In the reactor callback, a hard-coded string "ActiveX" is passed to
gp:Calculate-and-Draw-Tiles as the ObjectCreationStyle argument. But
what about the other times gp:Calculate-and-Draw-Tiles is invoked?
If you remember back to Lesson 4, it was pointed out that whenever you
change a stubbed-out function, you need to ask the following questions:
s Has the function call (invocation) changed? That is, does the function still
take the same number of arguments?
s Does the function return something different?
The same questions need to be asked any time you make a significant change
to a working function as you build, refine, and update your applications. In
this case, you need to find any other functions in your project that invoke
gp:Calculate-and-Draw-Tiles. VLISP has a feature that helps you do this.

To find all calls to gp:Calculate-and-Draw-Tiles in your project
1 In the VLISP text editor window, double-click on the word
gp:Calculate-and-Draw-Tiles within the gpdraw.lsp file.
2 Choose Search ® Find from the VLISP menu.
Because you preselected the function name, it is already listed as the string
to search for.
3 Select the Project button listed under Search in the Find dialog box.
When you select this option, the Find dialog box expands at the bottom, and
you can select the project to be searched.
4 Specify your current project name, then press the Find button.
VLISP displays the results in the Find output window:
5 Look at the results in the Find Output window and determine whether there
are any other locations in your code where you make a call to
gp:Calculate-and-Draw-Tiles. There should only be one: a location within
gpmain.lsp.
6 In the Find Output window, double-click on the line of code calling
gp:Calculate-and-Draw-Tiles.
VLISP activates a text editor window and takes you right to that line of code
in gpmain.lsp. The code currently appears as follows:
(setq tilelist (gp:Calculate-and-Draw-Tiles gp_PathData))
7 Replace the line of code with the following:
(setq tilelist (gp:Calculate-and-Draw-Tiles gp_PathData nil))
Why nil? Take another look at the pseudo-code:
If ObjectCreationStyle is nil, assign it from the BoundaryData.
Passing nil as a parameter to gp:Calculate-and-Draw-Tiles causes that
function to check the user’s choice of how to draw the tiles (as determined
by the dialog box selection and stored in gp_PathData). Subsequent calls
from the command-ended reactor callback, however, will override this
behavior by forcing the use of ActiveX.

Congratulations! You now have the basic reactor functionality in place. If
you prefer, copy the gpmain.lsp and gpdraw.lsp files from the
TutorialVisualLISPLesson7 into your working directory and examine the
completed, debugged code.
Your celebration party may be somewhat short-lived. There is still a lot of
work to be done, and it is all triggered from this rather innocuous looking
fragment of code in the gp:Command-ended function:
(gp:RedefinePolyBorder CurrentPoints reactorData)
) ;_ end of setq
Redefining the Polyline Boundary
You have worked hard to get to this point, and your brain has probably had
enough new concepts, terms, commands, and imperatives for a while. With
that in mind, it is recommended that you copy the sample code supplied
with the tutorial, rather than entering it on your own.
To copy the code used to redefine the polyline boundary
1 Copy the file gppoly.lsp from the TutorialVisualLISPLesson7 directory into
your working directory.
2 In the project window for your project, press the Project Properties button.
3 Add the gppoly.lsp file to the project.
4 Press OK to accept the project with the additional file.
5 In the project window, double-click the gppoly.lsp file to open it.
Looking at the Functions in gppoly.lsp
The file gppoly.lsp contains a number of functions required for straightening
a polyline when a single grip has been stretched. Only some of these func-
tions will be explained in depth in this tutorial.
NOTE This section of the Garden Path tutorial contains some of the most com-
plex code and concepts in the entire lesson. If you are a beginner, you may want
to jump ahead to the “Building an Application” section later in this chapter.

Redefining the Polyline Boundary | 115
The functions within the gppoly.lsp file are organized in a way that you may
have noticed in other AutoLISP source code files. The highest-level function,
often the main, or C: function (in this case, gp:Redefine-PolyBorder), is
located at the bottom of the file. The functions called within the main func-
tion are defined above it within the source file. This convention goes back to
the old days of programming, when some development environments
required that files be organized this way. With VLISP, this is a matter of per-
sonal style; there is no requirement that you organize your functions in any
specific sequence.
Before diving into the details, step back and look at what needs to be done
to recalculate and draw the garden path boundary. The following illustration
shows an example of a garden path, along with the association list key points
stored in the reactor data:
In this example, the 12 key point is the lower-left corner, 13 is lower-right,
and so on. If the user moves the upper-right point (the 14 key point), the pro-
gram will need to recalculate two existing points—the lower-right (13) and
upper-left (15).
Understanding the gp:RedefinePolyBorder
Function
The following pseudo-code shows the logic behind the main function,
gp:RedefinePolyBorder:
Function gp:RedefinePolyBorder
Extract the previous polyline corner points (12, 13, 14, and 15
key values).
Find the moved corner point by comparing the previous
polyline corner points with the current corner points.
(The one "misfit" point will be the point that moved.)
pt14
pt13
pt15
Recalculated
pt15
New
pt14
Recalculated
pt13
pt12

Set the new corner points by recalculating the two points
adjacent to the moved point.
Update the new corner points in the reactor data (that will
be stored back in the reactor for the modified polyline).
Update other information in the reactor data. (Start point,
endpoint, width, and length of path need to be recalculated.)
Understanding the gp:FindMovedPoint Function
The gp:FindMovedPoint function contains some very powerful LISP expres-
sions dealing with list manipulation. Essentially, what this function does is
compare the list of the current polyline points (after the user dragged one to
a new location) to the previous points, and return the keyed list (the 13
<xvalue> <yvalue>) for the moved point.
The best way to figure out how this function works is to step through the
code and watch the values that it manipulates. Set a breakpoint right at the
first expression (setq result . . .) and watch the following variables while
you step through the function:
s KeyListToLookFor
s PresentPoints
s KeyedList
s Result
s KeyListStatus
s MissingKey
s MovedPoint
The mapcar and lambda functions will be examined in the following section.
For now, however, follow the comments in the code to see if you can under-
stand what is happening within the functions.
Understanding the gp:FindPointInList Function
The function header in the source code explains how gp:FindPointInList
transforms the information it works with. Like the previous function,
Gp:FindMovedPoint, this function uses LISP’s list manipulation capabilities
to perform the work. When operating with lists, you will often see the mapcar
and lambda functions used together as they are here. At first, these are strange
and confusing functions, with names that do not indicate what they do.
Once you learn how to use them, however, you will find them to be two of
the most powerful functions within the AutoLISP repertoire. What follows is
a brief overview of mapcar and lambda.

Redefining the Polyline Boundary | 117
The mapcar function applies (maps) an expression to every item in a list. For
example, given a list of the integers 1, 2, 3, and 4, mapcar can be used to apply
the 1+ function to add 1 to each number in the list:
_$ (mapcar '1+ '(1 2 3 4))
(2 3 4 5)
An initial definition for mapcar is that it maps the function given in the first
parameter to the successive items in the second parameter—the list. The
resulting value from a mapcar operation is the list transformed by whatever
function or expression was applied to it. (Actually, mapcar can do more than
that, but for now this definition will suffice.)
In the supplied example, every value in the list '(1 2 3 4) was passed to the
1+ function. Essentially, mapcar performed the following operations, assem-
bling the resulting values in a list:
(1+ 1) -> 2
(1+ 2) -> 3
(1+ 3) -> 4
(1+ 4) -> 5
Here is another example of mapcar, this time using the null function to test
whether or not the values in a list are null (not true) values:
_$ (mapcar 'null (list 1 (= 3 "3") nil "Steve"))
(nil T T nil)
What happened in this code was essentially the following:
(null 1) -> nil
(null (= 3 "3") -> T
(null nil) -> T
(null "Steve") -> nil
You can use many existing AutoLISP functions within a mapcar. You can also
use your own functions. For example, imagine you have just created a very
powerful function named equals2:
_$ (defun equals2(num)(= num 2))
EQUALS2
_$ (mapcar 'equals2 '(1 2 3 4))
(nil T nil nil)
OK, so equals2 is not all that powerful. But it is in such cases that lambda
comes in handy. You can use lambda in cases where you do not want or need
to go through the overhead of defining a function. You will sometimes see
lambda defined as an anonymous function. For example, instead of defining
a function called equals2, you could write a lambda expression to perform
the same operation without the overhead of the function definition:
_$ (mapcar '(lambda (num) (= num 2)) '(1 2 3 4))
(nil T nil nil)

What happened in the code was this:
(= 1 2) -> nil
(= 2 2) -> T
(= 3 2) -> nil
(= 4 2) -> nil
With this knowledge, see if the gp:FindPointInList function makes sense.
Again, review the comments within the source code.
Understanding the gp:recalcPolyCorners
Function
The key to understanding how gp:recalcPolyCorners works is to revisit the
diagram showing what the key values of 12 through 15 represent:
In the diagram, the user moved the corner point associated with the key
value of 14. This means the corner points associated with 13 and 15 need to
be recalculated.
Point 15 needs to be moved along the current vector defined by point 12 to
point 15 until it lines up with the new point 14. The vectors from 12 to 15,
and from 14 to 15, must be perpendicular to each other. The same operation
must be applied to recalculate the new location for point 13.
Now take another look at the code to see if it makes sense.
Understanding the gp:pointEqual, gp:rtos2, and
gp:zeroSmallNum Functions
These three functions are required to get around one of the quirks of pro-
gramming in an AutoCAD system, which, as you are well aware, allows you
a great deal of precision. Occasionally, though, numbers are not quite precise
pt14
pt13
pt15
Recalculated
pt15
New
pt14
Recalculated
pt13
pt12

Wrapping Up the Code | 119
enough, due to the rounding up or down of floating point values defining
geometric positions. You must be able to compare one set of points with
other points, so you must deal with these cases.
Have you ever noticed that occasionally, when you list the information asso-
ciated with an AutoCAD entity, you see a value such as 1.0e-017? This
number is almost zero, but when you are comparing it to zero within a LISP
program, almost does not count.
Within the garden path, you need to be able to compare numbers without
having to worry about the fact that 1.0e-017 is not quite zero. The
gp:pointEqual, gp:rtos2, and gp:zeroSmallNum functions handle any dis-
crepancies in rounding when comparing point lists.
This completes your tour of the functions in gppoly.lsp.
Wrapping Up the Code
So far, you have done the following in this lesson:
s Modified the gp:drawOutline function so that it returns the polyline
perimeter points in addition to the pointer to the polyline. You added this
information to the gp_PathData variable. This variable is stored with the
reactor data in the object reactor attached to every garden path.
s Updated the reactor functions in gpreact.lsp.
s Added functions xyzList->ListOfPoints, xyList->ListOfPoints, and
other utility functions to the utils.lsp file.
s Updated the gp:Calculate-and-Draw-Tiles function so that
ObjectCreationStyle is now a parameter to the function rather than a
local variable.
s Modified the call to gp:Calculate-and-Draw-Tiles in the C:GPath func-
tion within the gpmain.lsp file.
s Added gppoly.lsp to your project, and examined the functions within it.
Give the completed application a try. Save your work, then load in the
project sources, run the Gpath function, and try stretching and moving the
garden path boundary. Remember: if something is not working and you are
unable to debug the problem, you can load the completed code from the
TutorialVisualLISPLesson7 directory.

Building an Application
The final act within this tutorial is to take your garden path code and turn it
into a standalone application. This way, it can be distributed as a single exe-
cutable to any user or customer. Fortunately, this last set of tasks is probably
the easiest in this entire tutorial, as VLISP does practically all the work for
you.
NOTE It is recommended that you proceed with building an application only
if your code is in good working form. Make sure that you have tested your appli-
cation using the original source files, and that you are satisfied with the results.
Starting the Make Application Wizard
To assist you in creating standalone applications, VLISP provides the Make
Application wizard.
To run the Make Application wizard
1 To start the wizard, choose File ® Make Application ® New Application
Wizard from the VLISP menu.
2 Select Expert mode and press Next.
The wizard prompts you to specify the directory in which to store files cre-
ated by Make Application, and to name your application. Make Application
produces two output files: a .vlx file containing your program executable, and
a .prv file containing the options you specify to Make Application. The .prv
file is also known as a make file. You can use the make file to rebuild your
application, when necessary.
3 Specify your TutorialVisualLISPMyPath directory as the application
location, and call the application gardenpath. VLISP uses the application
name in the output file names (in this instance, gardenpath.vlx and
gardenpath.prv.)
Press Next to continue.
4 The application options are not covered in this tutorial. Accept the defaults
and press Next. (For information on separate namespace applications, see
“Running an Application in Its Own Namespace” in the Visual LISP Devel-
oper’s Guide.)
5 In this step, the wizard is prompting you to identify all the AutoLISP source
code files that make up the application. You could individually select the
LISP source files, but there is an easier way. Change the pull-down file type

Wrapping Up the Tutorial | 121
selection box so that “Visual LISP Project file” is shown, then press the Add
button. Select the Gpath project file and press Open.
NOTE Depending on how you worked through the tutorial, you may have sev-
eral Gpath project files showing up. Select the most recent file. If you copied in
the completed source code from Lesson 7, the project name to select should be
Gpath7.prj.
After selecting the project file, press Next to continue.
6 One advantage of compiled VLX applications is that you can compile your
dialog control files (.dcl) into the complete application. This reduces the
number of individual source files your end users need to deal with, and elim-
inates any of the search path problems when loading a DCL file.
Change the pull-down file type selection box so that “DCL files” is shown,
then press the Add button. Select the gpdialog.dcl file, then press Open.
Press Next to continue building the application.
7 Compilation options are not covered in this tutorial. Accept the defaults and
press Next. (For information on compile options, see “Optimizing Applica-
tion Code” in the Visual LISP Developer’s Guide.)
8 The final step is used to review the selections you’ve made. At this point, you
can select Finish. VLISP will begin the build process, displaying the results in
the Build Output window. Several intermediate files will be produced, as your
individual source code files are compiled into a format that can be linked
into the single VLX application.
When it is all complete, you’ll have an executable file named gardenpath.vlx.
To test it, do the following:
s From the Tools menu in AutoCAD, select Load Application.
s Load the gardenpath.vlx application that was just created and is found in
the TutorialVisualLISPMyPath directory.
s Run the gpath command.
Wrapping Up the Tutorial
You have finally made it to the end of the path! As you have discovered, a lot
of material was covered in this tutorial. Both AutoLISP concepts and VLISP
operations have been introduced. The “garden path revisited” was designed
to give you a sampling of many topics and concepts. You might be interested
in more information. The following is a brief bibliography of some common
LISP and AutoLISP books.

LISP and AutoLISP Books
AutoLISP Books
AutoLISP: Programming for Productivity, William Kramer, Autodesk Press,
ISBN 0-8273-5832-6.
Essential AutoLISP, Roy Harkow, Springer-Verlag, ISBN 0-387-94571-7.
AutoLISP in Plain English: A Practical Guide for Non-Programmers, George O.
Head, Ventana Press, ISBN: 1566041406.
General LISP Books
LISP, 3rd Edition, Patrick Henry Winston and Berthold Klaus Paul Horn,
Addison-Wesley Publishing Company, ISBN 0-201-08319-1.
ANSI Common Lisp, Paul Graham, Prentice Hall, ISBN 0-13-370875-6.
Looking at LISP, Tony Hasemer, Addison-Wesley Publishing Company,
ISBN 0-201-12080-1.
Common LISP, The Language, Second Edition, Guy L. Steele, Jr., Digital Press,
ISBN 1-55558-041-6.

123
Index
Symbols
(), matching, 70
//, as DCL comment code, 56
;, as AutoLISP comment code, 21, 24
> button (Project Properties dialog box), 54
_$ prompt, in Console window, 12
{}, in DCL, 58
2D points
converting 3D points to, 35–36
converting lists of, to lists of lists, 105
3D points
at specified angle and distance from a
point, 41
converting lists of, to list of lists, 105
converting to 2D points, 35–36
3dPoint->2dPoint function, 35–36
A
action_tile function, 61–63
actions, assigning to tiles, 61–63
ActiveX functions
command function and, 37, 81
entity creation. See object creation
entmake function and, 37, 81
global variables and, 44
loading ActiveX, 43, 47
model space pointer and, 43–44, 47–48
object creation using, 37, 42–49, 57, 80,
105, 110–114
object model structure for, 42
passing parameters to, 38
radio button for, 56
reactors and, 105, 110–114
real numbers required by, 35
return values from, 35, 42
translating VBA syntax into ActiveX calls,
42
variants
constructing from a list of points,
44–46
defined, 44
vla- prefix and, 42
Add Watch button (Watch window), 29
Add Watch command (Debug menu), 20
adding
files to projects, 114
reactor callback functions, 91
variables to Watch window, 20, 29–30
See also assigning; attaching; creating;
defining
analyzing. See inspecting; watching variables
angles
converting degrees to radians, 34–35,
40–41
drawing path at any angle, 40–41
anonymous functions, 117–118
append function, 45, 77
applications, 120
creating, 120–121
apply function, 45
arguments. See parameter passing
arrays of polyline points, constructing, 44–45
arrow (>) button (Project Properties dialog box),
54
assigning
actions to tiles, 61–63
See also adding; attaching
assoc function, 40
association lists (assoc lists), 17–19
advantages, 18
in gp:getPointInput function, 17–19, 20,
22–23, 31
inspecting (parsing), 39–40
key values, 17–18, 40
passing to functions, 39–40
using, 18–19
associativity between tiles and path, breaking,
98, 102, 103, 104
atof function, 63
attaching
reactors, 87
See also adding; assigning; detaching

124 | Index
AutoCAD
command line, 37
crashing, 92, 96, 106
DCL files and, 58
emulating in AutoLISP programs, 15
entities. See entities
minimized window, gpath prompts and, 12
reactors and. See reactors
waiting for control to return from, 7
AutoLISP code
checking, 8, 11
color syntax coding, 8, 58
commenting, 21, 24
debugging. See debugging
modularizing, 52–53
revising, 21–23, 112–114
selecting blocks of, 70
testing, 23, 81
automatic garbage collection, 14
automatic word completion, 71–72
Automation objects, 42
B
blocks of code, selecting, 70
boundaries
ActiveX and, 42–48
angle of path and, 40–41
dialog box creation for, 56–58
dialog box defaults for, 59
erasing, reactors and, 85–94, 96–97, 103,
107
line styles
default type, 59
defining radio buttons for specifying,
56–57
drawing specified style, 66–67
reactors and, 104–105, 107–110
modifying
GRIP commands and, 106, 107
grip mode of STRETCH command
and, 98, 103, 114–119
reactors and, 85–94, 98–119
vertices
comparing, 119
determining, 40–41, 118
finding moved points, 116
finding points in lists, 116–118
reactors and moving, 85–94, 98–119
variant array of, 44–46
See also points
See also gp:drawOutline function
BoundaryData variable, 39–40, 111
boxed_radio_column DCL directive, 56
braces ({}), in DCL, 58
breakpoints, 24–31
clearing all, 31
clearing individual, 26, 31
breakpoints (continued)
cursor and, 27
Debug toolbar and, 25–26, 27
defined, 24
setting, 26–27
stepping through code from, 27–29
Btm button (Project Properties dialog box), 54
Build Output window
application building and, 121
syntax checking and, 11
building. See creating
buttons
assigning actions for dialog boxes, 62–63
creating for dialog boxes, 56, 57
Debug toolbar, 25–26, 27–29, 31
Project Properties dialog box, 53–54
VLISP toolbar, 25, 44, 53
Watch window, 20
C
C: (prefix), 9
C:GPath function, 7–8, 22–23, 48, 65–66, 67,
88–91, 101
Calculate-and-Draw-Tiles function, 74–77,
110–114
Calculate-Draw-TileRow function, 76–81
callback functions
ActiveX and, 105, 110–114
adding, 91
adding functionality to, 102–103
defined, 84
editor reactors and, 86–87, 96, 98,
104–107
object reactors and, 86, 96, 98, 103, 106,
111–119
planning and designing, 85–86, 104
See also specific callback functions
Cancel button
defining in DCL, 56
procedure when user presses, 63–64
case sensitivity, Help system and, 44
cdr function, 40
changing
boundaries
grip mode of STRETCH command
and, 98, 103, 114–119
value of variables while program is
running, 30
See also clearing; detaching; erasing;
removing
Check Text in Editor command (Tools menu), 11
checking code. See syntax checking
circles. See tiles (garden path)
clean-all-reactors function, 92
CleanReactors function, 92

Index | 125
Clear All Breakpoints command (Debug menu),
31
clearing
all breakpoints, 31
individual breakpoints, 25, 31
See also detaching; erasing; removing
command function
ActiveX and, 37, 80
entity creation via, 57, 81, 105
reactors and, 88, 105
command line, in AutoCAD, 37
command-ended function. See
gp:command-ended function
commands
entering in Console window, 12
See also specific commands
command-will-start function, 97, 102, 103
comments
AutoLISP, 21, 24
DCL, 56
comparing floating point values, 119
Complete Word by Apropos feature, 72
Complete Word by Match command (Search
menu), 71
completing words automatically, 71–72
concatenating lists, 45
Console window
entering commands in, 12
history command, 17
constructing. See creating
Continue button (Debug toolbar), 31
converting
degrees to radians, 34–35, 40–41
lists of points to variant arrays, 44–46
real numbers to strings, 61
strings to real numbers, 63
3D point lists to list of lists, 105
3D points to 2D points, 35–36
2D point lists to list of lists, 105
corner points. See boundaries, vertices
crashing AutoCAD, reactors and, 92, 94, 106
creating
applications, 120–121
boundaries. See boundaries
breakpoints, 26–27
buttons in dialog boxes, 56
dialog box default values, 59
dialog boxes, 56–58
entities (objects). See objects, creating
files, 8, 120–121
projects, 53–55
tiles. See tiles (garden path)
variant arrays of polyline points, 44–46
See also adding; assigning; attaching;
defining
curly braces ({}), in DCL, 58
cursor, breakpoints and, 27
D
database reactors, 84
DCL (dialog control language)
AutoCAD and, 58
comment code for, 56
defining dialog boxes, 55–58
loading files, 60–61
previewing files, 58–59
saving files, 58
See also dialog boxes
sources of information on, 55
syntax coloring scheme and, 58
unloading files, 63
VLX applications and, 121
.dcl file extension, 55, 121
Debug menu
Add Watch command, 20
Clear All Breakpoints command, 31
Watch Last Evaluation command, 30
Debug toolbar
breakpoints and, 25–26, 27
Continue button, 31
described, 25–26
Reset button, 29
Step Indicator, 26, 27
Step Into button, 28, 30, 31
Step Out button, 27, 30–31
Step Over button, 27–28
stepping through code and, 25, 27–32
Toggle Breakpoint button, 26, 31
debugging, 14–32
association lists and, 17–19
breakpoints and, 24–28
changing value of variables while program is
running, 30
commenting and, 24
global variables and, 14–15, 30, 31
local variables and, 14–17, 29–30
modularizing, 52
revising code, 21–23
stepping through code, 27–31
watching variables, 20, 29–30
defaults, dialog box values, 56, 59, 61
defining
functions. See defun function statement
goals, 6
See also adding; creating
defun function statement
ActiveX loading and, 47
described, 9
global variable assignment and, 47–48
defun function statement
stubbed-out functions and, 10–11

126 | Index
defun function statement (continued)
variable declaration and, 15
Degrees->Radians function, 34–35, 38–39, 41
deleting. See clearing; detaching; erasing;
removing
designing
programs, 5–12
reactor callback functions, 85–86, 104
See also planning
detaching
toolbars, 25
See also attaching; clearing; erasing;
removing
assigning actions to tiles, 61–63
default values, 56, 59, 61
defining, 55–58
initializing, 61
interfacing with, from AutoLISP code,
59–64
loading, 60–61
overview, 55
previewing, 58–59
saving, 58
starting, 63
unloading, 63
VLX applications and, 121
See also specific dialog boxes
dialog control language (DCL). See DCL (dialog
control language)
DialogInput function. See gp:getDialogInput
function
dialogLoaded variable, 60
dialogShow variable, 60, 61
directories
source code, 3
working directory, 3
displaying program output, 9
document reactors, 84
done_dialog function, 63
double slash (//), as DCL comment code, 56
doubles, arrays of, 44–46
drawing. See creating
drawOutline function. See gp:drawOutline
function
DXF reactors, 84
E
Edit menu, Parentheses Matching command, 70
editor reactors
callback functions and, 86–87, 96, 98,
104–110
described, 84, 86, 87
types of, 84
where to attach, 87
EndPt variable, 16, 17, 29–30, 31
Enter Expression to Watch dialog box, 20
entget function, entmake function versus, 37
entities. See objects
entmake
entity creation via, 80
entmake function
ActiveX and, 37, 56, 80
entget function versus, 37
entity creation via, 37
erase-tiles function, 106–107
erasing
boundaries and tiles, reactors and, 85–94,
96–97, 103, 107
tiles and redrawing when boundaries
change, reactors and, 85–94, 98,
104–119
See also clearing; detaching; removing
error checking
color coding and, 8, 58
syntax checker, 11
See also debugging
error messages, displaying, 9
executing. See running
exiting
programs quietly, 9
F
File menu
Make Application command, 120–121
New File command, 8
Save All command, 68
Save As command, 58
files
adding to projects, 114
creating, 8
creating application, 120–121
loading
DCL files, 60–61
program files, 12, 68
project files, 55, 68
make, 120
managing via projects, 53–55
organizing contents of source code, 115
saving all, 68
saving DCL, 58
unloading DCL, 63
Find command (Search menu), 113
finding. See searching
FindMovedPoint function, 116
FindPointInList function, 116–118
floating point values
comparing, 119
See also real numbers
Format AutoLISP in Editor command (Tools
menu), 9

Index | 127
formatting, 8
forward slashes (//), as DCL comment code, 56
functions
anonymous, 117–118
callback. See callback functions
checking, 8, 11
commenting, 21, 24
debugging. See debugging
defining. See defun function statement
exiting quietly, 9
help for, 44, 72–73
loading, 12
naming
finding and completing names, 72–73
organizing within source code files, 115
passing parameters to. See parameter passing
polar, 41, 76
return values. See return values
revising, 21–23, 112–114
running, 12
on individual elements in lists, 45,
116–118
stubbed-out
defining, 10–11
updating, 65–66
testing, 23, 81
variables. See variables
See also specific functions; utility functions
G
garbage collection, automatic, 14
garden path
angle of, 40–41
illustrated, 6, 77
width of, 59, 65, 66
See also boundaries; gp:drawOutline
function; gp:getDialogInput
function; gp:getPointInput
function; tiles (garden path)
gardenpath.prv file, 120
gardenpath.vlx file, 7, 120–121
getDialogInput function. See gp:getDialogInput
function
getdist function, 16
getpoint function, 16
getPointInput function. See gp:getPointInput
function
global variables, 14–15
ActiveX entity creation and, 44
debugging and, 14–15, 30, 31
defined, 14
defun function statement and, 47–48
local versus, 14
model space and, 43, 47–48
reactors and, 87, 96–97, 102, 103, 106,
107
uses for, 44
global variables (continued)
See also specific global variables
goals, defining, 6
gp: prefix, 9
gp:Calculate-and-Draw-Tiles function, 74–77,
110–114
gp:Calculate-Draw-TileRow function, 76–81
gp:clean-all-reactors function, 92
gp:command-ended function, 85–87, 104–105,
107–110
code for, 107–110
designing, 85–86, 104
gp:outline-changed function and, 85–86
gp:outline-erased function and, 96, 97
multiple entity types and, 104–105
multiple reactors and, 86–87
gp:command-will-start function, 97, 102, 103
gp:drawOutline function, 38–48
ActiveX and, 42–48
angle of path and, 40–41
basic code for, 46–48
boundary line style selection code for,
66–67
passing parameters to, 39–48
pointer to model space, 42–44, 47–48
purpose of, 9, 11
reactors and, 99–101
return values
polyline perimeter point list, 99–101
polyline pointer, 43–47
stubbing-out, 10–11
vertices
setting up, 40–41
See also boundaries
gp:erase-tiles function, 106–107
gp:FindMovedPoint function, 116
gp:FindPointInList function, 116–118
gp:getDialogInput function
adding dialog box to, 55–66
purpose of, 9
return value, 65
gp:getPointInput function, 16–31
angles and, 40
breakpoints and, 24–28
how it works, 16–17
local variables in, 15, 30–31
purpose of, 9–11
return values
as 3D points, 35–36
association lists of, 17–19, 20, 22–23,
31
regular lists of, 16–17
storing in variables, 19
revising code, 21–23
stepping through, 25–31

128 | Index
gp:getPointInput function (continued)
gp:list->variantArray function, 45–46
gp:outline-changed function, 85–86, 103
gp:outline-erased function, 96, 97, 103
gp:pointEqual function, 119
gp:recalcPolyCorners function, 118
gp:RedefinePolyBorder function, 115
gp:rtos2 function, 119
gp:Safe-Delete function, 107
gp:zeroSmallNum function, 119
gp_dialogResults variable, 66
gp_PathData variable
described, 22–23
gp:drawOutline function and, 39, 48
gp:getDialogInput function and, 19, 66
watching value of, 20
gp_spac variable, 63
gp_trad variable, 63
gpath command, 7, 9
GPath function. See C:GPath function
gpath.prj file, 53
gpdialog.dcl file, 58, 59, 121
gpdraw.lsp file, 66, 70, 71, 72, 73, 80
gp-io.lsp file, 52
gpmain.lsp file
See also C:GPath function
position in project files, 54
reactors and, 88–91
return values and, 10
using the supplied, 11
gppoly.lsp, 114–119
gpreact.lsp file, 91–92, 102–104, 106–107
GRIP commands, reactors and, 106, 107
grip mode of STRETCH command, reactors and,
98, 103, 114–119
H
HalfWidth variable, 16, 17, 29–31
Help button (VLISP toolbar)
help, for functions, 44–45, 72–73
highlighting blocks of code, 70
history command, 17
I
I-beam cursor, in Debug toolbar, 27
initializing dialog boxes, 61
input. See gp:getDialog Input function;
gp:getPointInput function; entries
beginning with get, vla-get, and vlax-get
Inspect command (View menu), 39–40
Inspect window
Add Watch command, 20
Inspect command, 39
inspecting
association lists, 39–40
variables, 19, 20
installing tutorial, 3
integers, ActiveX functions and, 35
Interface Tools command (Tools menu), 58, 59
K
key values
AutoCAD and, 17–18
in associated lists, 17–18, 40
L
lambda function, 116–118
*Last-Value* variable, 31, 30
lightweight boundary lines. See boundaries, line
styles
line styles. See boundaries, line styles
linker reactors, 84
list->variant Array function, 45–46
lists
association. See association lists
comparing lists of points, 119
concatenating, 45
converting 2D point lists to list of, 105
converting 3D point lists to list of, 105
converting lists of points to variant arrays,
45–46
executing functions on individual elements
in, 116, 118
finding points in, 116, 118
of return values, 16
association lists. See association lists
passing to functions
association lists, 39, 40
regular lists, 45
testing for null values in, 117
Load Text in Editor command (Tools menu), 12
load_dialog function, 60
loading
ActiveX, 43, 47
DCL files, 60–61
functions, 12, 43, 47
programs, 12, 68
project files, 54, 68
See also unloading
selected code, 3, 39, 70, 106
local variables, 14–16
declaring, 15, 111
defined, 14
global versus, 14

Index | 129
local variables (continued)
nil return values and, 31
See also specific local variables
watching, 20, 29
*lostAssociativity* variable, 102, 103
M
Make Application command (File menu),
120–121
make files, 120
managing files via projects, 53–55
mapcar function, 45, 116, 117
matching parentheses, 70
memory, local and global variables and, 14
messages, displaying program, 9
minimized windows
AutoCAD window, gpath prompts and, 12
VLISP, accessing, 53
model space
global variables and, 43–44, 47, 48
obtaining a pointer to, 43–44, 47, 48
obtaining a pointer to global variables
model space and, 43
*ModelSpace* variable, 42, 44, 47, 53
modifying. See changing
modularizing, 52, 53
Mouse reactors, 84
moving
boundaries. See boundaries, modifying
toolbars, 25
N
naming functions, 9
finding and completing names, 72–73
new features, 2
New File command (File menu), 8
New Project command (Project menu), 53, 54,
55
new_dialog function, 61
NewReactorData parameter, 111
nil parameters, 113
nil return values, 10, 31
non-linear reactor sequences, 106–107
null values, testing for, in lists, 117
numbers
ActiveX functions and, 35
comparing floating point values, 119
converting real numbers to strings, 61
converting strings to real numbers, 63
integer versus real, 35
passing to functions, 38, 39
O
object reactors
callback functions and, 99, 103, 106
object reactors (continued)
described, 84, 87
where to attach, 87
ObjectARX applications, reactors and, 84, 99
ObjectCreationFunction variable, 80
ObjectCreationStyle parameter, 80, 110–114
ObjectCreationStyle variable, 110, 111
objects
ActiveX object model structure, 42
Automation objects, 42
creating
dialog box for, 56–58
with ActiveX, 37, 42–48, 57, 80, 105,
110–114
with command function, 57, 81
with entmake function, 37, 57
handling multiple types of, 104–105
key values and, 17–18
reactors and. See object reactors
returning entity data to AutoLISP, 17–18
VLA-objects, 42
objects. See entities (objects)
OK button
assigning actions to, 62
defining in DCL, 57
procedure when user presses, 62–64
Open Project command (Project menu), 68
opening
project files, 54, 55, 68
See also loading
organizing functions within source code files,
115
outline. See also gp:drawOutline function
outline-changed function, 85, 86, 103, 106
outline-erased function, 86, 96, 97, 103
output
displaying program, 11
vla-put functions, 42
See also gp:drawOutline function
P
parameter passing, 38, 39, 40
association lists, 39, 40
declaring variables as both parameters and
local variables, 111
lists, 45
nil parameters, 113
numbers, 38, 39
variables, 39
See also specific parameters
parentheses [()], matching, 70
Parentheses Matching command (Edit menu),
70
parsing association lists, 39, 40
passing parameters
ActiveX functions, 42
passing parameters. See parameter passing

130 | Index
path. See garden path
PathAngle variable, 40, 41
PathLength variable, 41
pausing program execution. See breakpoints
planning
reactor callback functions, 85–86, 104
reactors, 95, 102
See also designing
utility functions, 33–36
pline variable, 42, 43, 47
pointEqual function, 118
pointers
to model space, 43–44, 47
VLISP pointer, 7
PointInput function. See gp:getPointInput
function
points
3D points at specified angle and distance
from a point, 41
comparing, 118
converting 3D points to 2D points, 35–36
converting lists of 2D/3D points to list of
lists, 105
determining corner, 41, 118
finding in lists, 116, 117, 118
finding moved, 116
reactors and moving, 85–94, 97–119
polar function, 41, 76
polyline borders. See boundaries
PolylineList variable, 101
polyPoints variable, 100, 101
*polyToChange* variable, 97, 102, 103
previewing dialog boxes, 58
princ function, 9
.prj file extension, 68
programs. See code; functions
Project menu
New Project command, 53–54
Open Project command, 68
Project Properties button (project window), 91,
114
Project Properties dialog box, 53, 54
project window, 55, 114
projects
adding files to, 114
creating, 53–55
described, 53
loading and running all files in, 68
searching, 113
prompts
_$ prompt in Console window, 12
displaying program, 9
minimized AutoCAD window and, 12
.prv file extension, 120
Q
quiet exit, 9
quoted symbols, 11
R
radians, converting degrees to, 34–35, 41
radio buttons
in dialog boxes, 56, 57
See also buttons
radio_column DCL directive, 56
radius of tiles
default, 57, 61
specifying, 56
reactors, 83–114
attaching, 87
AutoLISP applications and, 113
for boundaries, 85–94, 97–119
callback functions
adding, 91
adding functionality to, 102–110
defined, 84
editor reactors and, 86–87, 96, 97–98,
104–107
object reactors and, 86, 96, 97, 103,
106, 110–119
planning and designing, 85–87, 104
See also specific callback functions
crashing AutoCAD and, 92, 94, 96, 106
defined, 84
editor
callback functions and, 97–98,
104–107
described, 84, 86, 87
where to attach, 87
editors
types of, 84
event selection, 85
global variables and, 87, 96–97, 102–103,
106
grip mode of STRETCH command and, 98,
103, 114–119
multiple, 86–87
multiple entity types and, 104–105
non-linear sequences of, 105–107
object
callback functions and, 86, 96, 97,
103, 106, 111–119
described, 84, 87
where to attach, 87
ObjectARX applications and, 84, 99
planning the overall process, 96–101
removing, 92, 96
returning to VLISP from AutoCAD and, 93

Index | 131
reactors (continued)
storing data with, 88, 99–101
testing, 92–94
tiles and, 85–94, 96–97, 98, 103–119
trace sheets for, 93–94, 97, 105
transient versus persistent, 94
types of, 84, 86, 87
*reactorsToRemove* variable, 96
real numbers
ActiveX functions and, 35
converting real numbers to strings, 61, 63
floating point values, 119
recalcPolyCorners function, 118
RedefinePolyBorder function, 115
reference works. See resources
reformatting, 9
regular lists, 16
removing
reactors, 92, 96
See also clearing; detaching; erasing
requirements, 2
Reset button (Debug toolbar), 29
resources
DCL, 55
LISP and AutoLISP, 122
return values
ActiveX functions, 43
defined, 10
gp:drawOutline function, 46, 47, 99–101
gp:getDialogInput function, 19
gp:getPointInput function.
See gp:getPointInput function,
return values
lists of
association. See association lists
regular, 16–17
nil return, 10, 31
storing in variables, 19
true return, 10
revising code, 21–23, 112–114
rotating boundaries. See boundaries, modifying
rows. See tiles (garden path)
rowStartPoint variable, 76
rtos function, 61
rtos2 function, 118, 119
running
and stepping through, 27–31
breakpoints with, 24–31
dialog boxes, 63
functions, 12
on individual elements in lists, 45, 117
garden path example, 7
programs, 12, 68
project files, 68
tutorial, 2
VLISP, 7
S
Safe-Delete function, 107
*Safe-to-Delete* function, 107
Save All command (File menu), 68
Save As command (File menu), 8
saving
all files, 68
DCL files, 58
scaling boundaries. See boundaries, modifying
Search menu
Complete Word by Match command, 71
Find command, 113
searching
for closest match to complete a word, 71
for moved points, 116
for points in a list, 116–118
projects, 113
Select Window button (VLISP toolbar), 53
semicolon (;), as AutoLISP comment code, 21,
24
set_tile function, 61
setting. See adding; assigning; creating; defining
slashes (//), as DCL comment code, 56
source code
CD containing, 3
directories, 3
organizing functions within files of, 115
spacing of rows, 74
spacing of tiles, 74
default, 59, 65
specifying, 57
start_dialog function, 61, 63
starting
dialog boxes, 63
See also creating; running
StartPt variable, 16, 17, 29, 31
Step Indicator (Debug toolbar), 26, 27
Step Into button (Debug toolbar), 25, 28, 30, 31
Step Out button (Debug toolbar), 25, 31
Step Over button (Debug menu), 30
Step Over button (Debug toolbar), 25, 28
Debug toolbar and, 25, 27–32
exiting, 31–32
from breakpoints, 27, 28–29, 30, 31
watching variables while, 29–30
storing
data with reactors, 88, 99–101
return values in variables, 19
stretching boundaries, reactors and, 98, 103,
114–119
strings
converting real numbers to, 61
converting to real numbers, 63

132 | Index
stubbed-out functions
defining, 10–11
updating, 65–66
suspending program execution. See breakpoints
symbols
quoted, 11
T, 10
syntax checking
automated, 11
color coding and, 8, 58
T
T (symbol), 10
testing
code, 23, 81
reactor code, 92–94
See also debugging; syntax checking
“3D”, index entries beginning with. See Symbols
section of this index
tileList variable, 77
tiles (dialog box component), 56
tiles (garden path)
erasing when boundary is erased, 85–94,
96–97, 103, 107
first row of, 76
illustrated, 6, 73
radius and tile spacing
default, 59, 65
specifying, 57
reactors and, 85–94, 96–97, 103–119
redrawing when boundary is modified,
85–94, 98, 104–119
row spacing, 74
row-offset pattern, 73–74, 76–77
Toggle Breakpoint button (Debug toolbar), 25,
26, 31
toolbars
moving, 25
See also Debug toolbar; VLISP toolbar
Tools menu
Check Text in Editor command (Tools
menu), 11
Format AutoLISP in Editor command (Tools
menu), 9
Interface Tools command, 58
Load Text in Editor command, 12
Top button (Project Properties dialog box), 54
trace sheets, reactor, 93–94, 97, 105
true return value, 10
tutorial, overview, 3
“2D”, index entries beginning with. See Symbols
section of this index
U
unload_dialog function, 60, 63
unloading
DCL files, 63
utility functions
3dPoint->2dPoint, 35–36
gp:list->variantArray function, 45–46
xyList->ListOfPoints, 105
xyzList->ListOfPoints, 105
utils.lsp file, 52, 53, 54, 91, 92, 105, 105
V
values
for radio buttons in DCL, 56
See also key values; return values; variables
variables
breakpoints and, 24
changing value while program is running,
30
declaring, 38
passing to functions, 39
storing return values in, 19
variants (ActiveX)
constructing arrays of polyline points,
44–46
defined, 44
VBA syntax, translating into AutoLISP, 42
vertices. See boundaries, vertices; points
View menu
Inspect command, 39–40
Visual LISP Tutorial, 1
Visual LISP. See entries beginning with VLISP
vla- (prefix), 42
vla-addLightweightPolyline function, 42, 70, 72
vla-get functions, 42
vla-get-ActiveDocument function, 43
vla-get-ModelSpace function, 43
VLA-objects, 42
vla-put functions, 42
vla-put-closed function, 42
vlax-get-Acad-Object function, 43
vlax-make-safearray function, 46
vlax-make-variant function, 46
vlax-safearray-fill function, 46
vlisp command, 7
VLISP development environment
accessing minimized windows, 53
described, 2
reactors and returning from AutoCAD to,
93
VLISP pointer in, 7
waiting for control to return from
AutoCAD, 7
VLISP menu
Debug command. See Debug menu
Edit command. See Edit menu
File command. See File menu
Project command. See Project menu
Search command. See Search menu

Index | 133
VLISP menu (continued)
Tools command. See Tools menu
View command. See View menu
Window command, 53
VLISP toolbar
Help button, 72
Select Window button, 53
vl-load-com function, 43
vlr-commandEnded events, 87–91, 99
vlr-commandWillStart events, 99, 102
vlr-erased event, 103
vlr-modified event, 85
vlr-modified events, 103
vlr-object-reactor function, 88–91
VLX applications, 2, 120–121
.vlx file extension, 120
W
Watch command (Debug menu), Add, 20
Watch Last Evaluation command (Debug
menu), 30
Watch window
Add Watch button in, 29
Add Watch command and, 20
Watch Last Evaluation command and, 30
adding variables to Watch window, 20,
29–30
Debug toolbar and, 25
defined, 19
while stepping through code, 29–30
width of path, 59, 65, 66
Window command (VLISP menu), 53
windows. See minimized windows; project
window; specific windows
words, completing automatically, 71–72
working directory, 3
X
xyList->ListOfPoints function, 105
xyzList->ListOfPoints function, 105

(Manual) auto cad 2000 visual lisp tutorial (autocad)

(Manual) auto cad 2000 visual lisp tutorial (autocad)

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