Processing语言教程教授processing的使用技巧，具体方法和操作教程

LearningProcessing
Beginning
Daniel Shiffman
Graphics from http://www.learningprocessing.com/tutorials/

Section 1
基本概念
Invitation to Computer Science, Java Version, Third Edition 2

What is an image?
Digital
Camera
Source: A. Efros

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Image as Grid of Values
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GraphPaper
Every point on the screen is a pixel
It has a location: (x, y)
Learning Processing: Slides by Don Smith 6

Upper left corner is 0,0
X is ‘across’ (to right as x increases)
Y is ‘down’ (down as y increases)
CoordinateSystem
NOT the same as your Algebra coordinate system!

SimpleShapes
What do we need to specify a shape?
Point: x and y
Line: Two end points?
Rectangle: Two corners? Or ???
Ellipse: ????

Point
Note that x (across) comes first
In Processing: point(x, y);
lower case ‘point’
two ‘parameters’ in parenthesis
Semicolon;

Line
 Two Points: A and B
 In Processing: line(x1, y1, x2, y2);



lower case ‘line’
four ‘parameters’ in parenthesis
Semicolon;

Rectangle1
From Corner: One Point for top left corner
In Processing: rect(x, y, width, height);
lower case ‘rect’
four ‘parameters’ in parenthesis
Semicolon;
NOTE: This is the default mode (CORNER)

Rectangle2
From Center: One point, size
In Processing:
rectMode(CENTER);
rect(x, y, width, height);
Two lines of code

Rectangle3
CORNERS: Top Left point, Bottom Right point
In Processing:
rectMode(CORNERS);
rect(x1, y1, x2, y2);
Two lines of code

EllipseModes
Same as rectangle modes:
CENTER (x, y, width, height)
CORNER (x, y, width, height)
CORNERS (x1, y1, x2, y2)
Draws ellipse in a ‘Bounding box’
Circle is a ‘special case’ of an ellipse (width = height)

SizeMatters
You can specify the size of your ‘canvas’ at the
start of a ‘script’
size(width, height);
Use 200 x 200 to get started
It matches the ‘graphPaper200x200.doc’ file

Color: Grayscale
You can set the color of lines and background:
0 is black (no ‘light’)
255 is white (most ‘light’)
Some examples in processing:
background(255);
stroke(0);
fill(150);
// Sets background to white
// Sets outline to black
// Sets interior of a shape to grey
rect(50,50,75,100); // Draws shape with most recent settings

GrayscaleExample
To fill or not to fill
If noFill() is set, shapes have only an outline
What are the ‘default’ grayscales of:
Background:
Stroke:
Fill:

RGBColor
Color Mixing 101:
Red + Green = Yellow
Red + Blue = Purple
Green + Blue = Cyan (blue-green)
Red + Green + Blue = White
no colors = Black
 RGB Values
 Each color has a value between 0 and 255


0 means NONE of that color
255 means MAX of that color



Use fill(),background() or stroke() with three
parameters:
 fill(red, green, blue);
Then draw a shape!
// Bright red
// Dark red
// Pink (pale red)
ManualColors
background(255);
noStroke();
fill(255,0,0);
ellipse(20,20,16,16);
fill(127,0,0);
ellipse(40,20,16,16);
fill(255,200,200);
ellipse(60,20,16,16);

PickingColors
 Processing has a color selector to aid in
choosing colors.
 Access this via TOOLS (from the menu bar)
→ COLOR SELECTOR.

There is a fourth ‘parameter’ you can use:
Called ‘Alpha’
0 means transparent
255 means opaque
No fourth parameter means ‘100% opacity’
Transparency
// 50% opacity.
fill(255,0,0,127);
// 25% opacity.
fill(255,0,0,63);
rect(0,150,200,40);

NowGettoWork!
Plan a more interesting alien!
Use grayscale!
Black eyes
Gray body

Section 2
开发环境

Installing
Finding the files
Website: www. processing.org – click Download
Blackboard: Files, Tools folder
Version 2.1.1 is the most current
Download (110MB) processing-2.1-windows64
If you already have Java installed:
Install the Windows (Without Java) expert version instead
processing-xxx-expert.zip - From www.processing.org
Unzip , or open and extract files
Let it choose defaults (location…)
Installs Java SDK automatically and examples
Puts Java files in a folder under Processing
Works with XP and Win7
Installs an icon on your desktop
Learning Processing: Slides by Don Smith
24

WheredoesJavafitin?
Processing provides a
simple ‘front end’ to Java.
Processing requires Java
SDK to be installed
Software Development Kit
Processing has it’s own
library for graphics
Java’s library (API) can
also be used in
Processing
Processing Source code
Processing
Java Compiler
Portable Java Program
Processing
Library
Java
Library

TheJavaVirtualMachine(JVM)
Java was designed to run on embedded systems, it was
designed around a virtual machine
“Write once, run everywhere”
Called the JRE (Java Runtime Environment)
Portable Java Program
PC
Java VM
Windows
x86
Running
Java
Program
Mac
Java VM
OS X
G3/4/5
Running
Java
Program
Cell Phone
Java VM
Phone OS
CPU
Running
Java
Program
JRE

SketchMenuOptions
Processing has an ‘PDE’ called Sketch
File: New, Open, Quit, Examples!
Edit: Copy, Paste, Select, Indent, Comment…
Sketch: Run, Stop, Show Sketch folder…
Tools: Auto format, Color chooser…
Help: Getting Started, Reference, Find in Reference…

PDE
28
Menu
Toolbar
Sketch Tabs
Text Editor
Message Line
Text Area
Current Line#
To run: Menu Sketch, Run, Ctrl-R or Toolbar Run button
You either get a display window (all’s well) or an error in Message Area
Display
Window

Toolbarbuttons

GettingStarted
 Help, Getting Started goes to processing
website and explains:






Processing Development Environment (PDE)
 All menu options, hot keys
Sketchbook
Tabs, Multiple Files, and Classes
Coordinates
Programming Modes
Rendering Modes

SketchFilesandFolders…
The folder where you store your sketches is
called your ‘Sketchbook’
Sketch stores files under where Processing was
installed
May not be where you want.
Use File, Save As to select a folder on your flash drive
Processing remembers where you last saved
Each sketch has it’s own folder
File extension ‘PDE’ is a Processing Development Environment
file
Double click on PDE file to open Sketch for that folder

Whereareyourfiles?
Choose File,
Preferences
Select new location for default
Not flash drive (not always there)

YourFirstProgram
Open a new sketch
Default name is based on date/time
In the Text window, type:
// My first Program
Print(“Hello World by me”);
rect(10, 10, 50, 50);
One comment and two lines of code
Run it… If no errors,
What is in the Message/Text Area?
What is in the Display window?

Errors
The brown line tells you what is wrong
Editor window: The line with the error is highlighted
RECT should be lower case (rect)
 Note: Processing only shows one error at a time

Help,FindInReference
Double click key word (highlights in yellow)
Menu: Help, Find in Reference: (or Ctrl-Shift-F)
Does not work if word is mis-spelled
Normally goes directly to detailed page (local)
Usually provides an example

Lab: ZoogHeadstand
Draw your alien – Upside Down!
Use grayscale
White head
Black eyes
Gray body
Add a comment with your name at the top
Add: print(“Zoog Headstand by <Your name>”);
Save your sketch
To your flash drive
Submit your sketch (pde) via Blackbloard

Section 3
编程基础

Programflow
Games are written with ‘loops’
Like running a race
Prepare (put on shoes…)
Loop putting feet forward over and over
Run until the race is over
Remember that programs are made of parts:
Sequential
Conditional
Iterative

Usingyourfirst‘methods’!
setup()and draw()are ‘methods’
Think of them as named ‘blocks’ of code
You get to write the code inside the ‘block’
New symbols and words! (just look for now)
void
()
//
{ }

A‘block’ofcode
Parts of a program are separated into blocks
In Java, C, C++, PHP and many other languages:
Blocks are surrounded by curly braces: { ….. }
Think of blocks like an outline set of sub-steps:
1
1a
1b
2
Programmers (and editors) line up code in blocks
Usually indent the ‘statements’ inside the block

setup()anddraw()methods
When your program starts,
Processing:
Calls setup() once
Continues to call draw() unti
the program ends
Program Starts
Call setup()
Call draw()
Done
yet?
Yes
Program ends
No

CodeforZoogasadynamicsketch
All of your code can go into two ‘blocks’:

The‘invisible’lineofcode…
When does processing ‘paint’ the screen?

TrackingtheMouse
Processing keeps track of where the mouse is:
mouseX: The current X coordinate of the mouse
mouseY: The current Y coordinate of the mouse
These are both ‘key words’ that you can use!
Their values change as the mouse moves
An example:

MoreMousetracks…
Processing also keeps track of where the mouse
WAS the last time you left draw():
pmouseX: The previous X coordinate of the mouse
pmouseY: The previous Y coordinate of the mouse

Ascribbleapplication
 Just keep connecting the points where the
mouse was and it is now:

MouseclicksandKeypresses


Two ‘methods’ that you can
write to handle events that
might happen:
Processing ‘calls’ your
method when events occur:
 mousePressed()
 keyPressed()

Processingsetup()method
Things that you may use during setup():
size(200,200);
smooth();
frameRate(30);
background(255);
// defaults to 60 frames/sec
// clear the screen
Each may be used for their own purposes
Some may also be used in draw()methods
What would this do to your drawing if the
background(255)call was in draw()?

Usingbackground(255)
void setup() {
size(200,200);
background(255);
}
void draw() {
line(mouseX, mouseY, 100,100);
}
void setup() {
size(200,200);
}
void draw() {
background(255);
line(mouseX, mouseY, 100,100);
}
49

Try these

Section 4
变量

Whatisavariable?
Storage Analogies:
Different sizes
Like a bucket
Like a locker
Graph Paper/Spreadsheet
Many ‘storage’ places, all with
unique locations (x,y)
In Excel, E3 could be named ‘Billys
Score’
Billy’s score can change!
A B C D E F
1
2
3
4
5

Whatisavariable?
In Algebra:
x=y*z
Named with single letters to represent some number
In Programming:
We use longer, more descriptive names
Variables refer to ‘memory locations’
Stored in ‘RAM’
Random Access Memory
Have a ‘size’
How many bytes of memory ‘wide’

Variablesmustbe‘Declared’
What is a Declaration?
Programmer tells the compiler:
Type
Name
;
What is a Type?
Each type requires a specific amount of storage
‘Primitive’ types include three main categories
Integers – Whole Numbers (positive and negative), no fractions
Floating point – Numbers with fractional parts and exponents
Characters – One letter that you can type
A, B, C, a, b, c, 1, 2, 3, %, &….

AllPrimitiveTypes
Integer Types
byte: A very small number (-127 to +128)
short: A small number (-32768 to +32767)
int:
long:
A large number (-2,147,483,648 to +2,147,483,647)
A huge number
Floating Point Types
float: A huge number with decimal places
double: Much more precise, for heavy math
Other Types
boolean: true or false
char: One symbol in single quotes ‘a’

55
PrimitiveTypeStorage
Integer Types
byte:
short:
int:
long:
float:
double:
Other Types
boolean:
char:

PrimitiveTypeExamples
Integer Types
byte:
short:
int:
long:
123
1984
1784523
234345456789
float:
double:
4.0
3.14159
Other Types
boolean: true
char: ‘a’

Numericversus‘Character’types
How do you decide if you need a numeric or
a character type?
If you plan on doing ‘math’ on the variable, then
you MUST use a numeric type
What is the letter ‘a’ times the letter ‘c’?
Notice the single quotes around characters
If you plan on using “Strings” (later), they are just
words made up of characters.
“Bob” and “Mary” are Strings (of characters)
Notice the double quotes around strings
What is the string “Bob” times the string “Mary”?
57

DeclaringandInitializingVariables
What is Initialization?
Setting an initial value into the contents of the variable
Pseudocode: Set NumPlayers to 5
Can be done in two ways:
During Declaration: On one line
int count = 50; // declare and initialize
After declaration: On two lines
int count;
count = 50;
// declare the variable
// initialize the value
Can also be initialized with a calculation!
int max = 100;
int min = 10;
int count = max – min; // calculation

PongVariables
What variables would be required to play?
Scores?
Paddle locations?
Ball location?
Net location
Screen Size?
59

NamingVariables
There are some ‘rules’ and some ‘best practices’
Rules
Letters, Digits and underscore ( _ ) are OK to use
Cannot start with a digit ( 0,1,…9 )
Cannot use reserved words
mouseX, int, size..
Best Practices
Use descriptive names
boolean moreToDo;
Use ‘camelHump’ notation
Start with lower case
Each new word starts with Upper Case

DeclarationandInitializationExamples
Type name (optional initialization) ;
int count = 0;
char letter = 'a';
double d = 132.32;
boolean happy = false;
float x = 4.0;
float y;
// Declare an int , initialized to 0
// Declare a char, initialized to 'a'
// Declare a double, initialized to 132.32
// Declare a boolean, initialized to false
// Declare a float, initialized to 4.0
// Declare a float (no assignment)
float z = x * y + 15.0; // Declare a float, initialize it to
// x times y plus 15.0.
After declaration Assignments:
count = 1;
letter = ‘b’;
happy = true;
y = x + 5.2; // Assign the value of x plus 5.2

DeclarationandInitializationIssues
You can only initialize a variable to a value
of the same, or compatible type:
Which initializations are compatible?
int count = ‘a’;
char letter = 0;
double deposit = “Fred”;
boolean happy = 1;
float feet = 6;
int inches = feet * 12;
long giant = feet * 3.0;

DeclarationandInitializationIssues
You can only initialize a variable to a value
of the same, or compatible type.
Which initializations are compatible?
int count = ‘a’;
char letter = 0;
double deposit = “Fred”;
boolean happy = 1;
float feet = 6;
int inches = feet * 12;
long giant = feet * 3.0;

WheretoDeclareVariables
Remember that your code is in ‘blocks’
Variables can go inside or outside these blocks
For now, we will put them ‘outside’ (before) blocks

VaryingVariables: Example
Remember that processing calls draw()in a loop
If you want the variable to change every time:
Declare and initialize it outside of draw()!
Change it inside draw()!
Moves as circleX increases 

Callto
draw()
circleX
1 0
2 1
3 2
4 3
5 4
…
200 199
66
WhathappensinPre-example?
circleX Is initialized to 0
Used first time draw()is called
ellipse(circleX, circleY, 50,50);
Then circleX = circleX + 1;
Next time draw()is called, circleX is 1
Next time draw()is called, circleX is 2
.. Until circleX is over 200, and the circle just
moves off the right side of the screen, never to be
seen again!
It is often useful to make a ‘table’ of all of the
variables that are being changed every time
through a ‘loop’

Callto
draw()
circleX circleY circleW circleH
1 0 0 50 100
2 0.5 0.5 50.5 100.5
3 1.0 1.0 51 101
10 4.5 4.5 54.5 104.5
30 14.5 14.5 64.5 114.5
100 49.5 49.5 99.5 149.5
200 99.5 99.5 149.5 199.5
UsingManyVariables
Make things more interesting using more variables!
Declare and initialize them outside of draw()!
Change them inside draw()!

SystemVariables
Processing provides many ‘built-in’ variables:
These are not for you to play with, but may change!
mouseX , mouseY, pmouseX and pmouseY
width: Width (in pixels) of sketch window
height: Height (in pixels) of sketch window
frameCount: Number of frames processed
frameRate: Rate (per sec.) that frames are processed
screen.height, screen.width: Entire screen
key: Most recent key pressed on keyboard
keyCode: Numeric code for which key pressed
mousePressed: True or false (pressed or not?)
mouseButton: Which button (left, right, center)

Random: Varietyisthespiceoflife
Processing (and all programming languages)
provide a way to get a random value when your
program runs.
random() is a ‘function’ that returns a float
You can assign this number to a variable and use it!
Some examples:

Whatisthat(int)and(1,100)stuff?
(int)
Since random()returns a floating point number
and w is an int, we need to change the type from
float to int.
This is called ‘casting’
random(1,100) ;
(1,100) are ‘parameters’ which tell the random
function the range of numbers to return
w will be between 1 and 99 (not quite 100)
70

MakeZoogMove!
Use variables to make Zoog move and change!
1) Make Zoog rise from below the screen
Need variables for the Zoog’s X and Y locations
Note: Locations of ALL of Zoog’s parts need to use them
If left eye is left 30 and down 50 from the center of the head:
ellipse( zoogX – 30, zoogY + 50, 20, 30);
2) Change his eye color randomly as he moves
Need variables for Zoog’s eye color (R,G and B)

Lab: MovingZoog
Use variables and random() to make a Zoog
move from upper left to lower right of the screen.
Starting point is provided (Example 4.8)
Plan!
Declare variables
Use variables
Use Random

1 2 3 4 5 6 7 8 9 10
73
Whydowecare(aboutarrays)?
What if you have a whole bunch of cars (or aliens
or balls or ???) bouncing around the screen?
How do we keep track of where each one is?
int car1X, car1Y, car2X, car2Y, car3X, car3Y……
How about keeping them in a ‘table’ or a ‘grid’
CarX table:
Each ‘column’ has a number
You can refer to CarX table, column 3 for Car3…
Note that all of the values in the row must be the
same data type

WhentouseanArray
Any time a program requires multiple instances
of similar data, it might be time to use an array.
For example, an array can be used to store:
The scores of four players in a game
A selection of 10 colors in a design program
A list of fish objects in an aquarium simulation
The days per month in a scheduling program

75
Whatisanarray?
A variable is a named
location in memory.
An array is a named set
of locations in memory
A ‘list’ of variables
Each element of the list
has a number called an
‘index’
Starts at 0!

76
Whystartat0? Whynot1?
Which of the following is why arrays start at 0?
A)
B)
C)
D)
Because programmers think that way
Because I say so
So that programmers can make ‘the big bucks’
So you can use loops easily to ‘walk’ the array
Here’s a preview of adding up all the ‘votes’:
int sumArray(int size) {
int sum = 0;
for (int c = 0; c < size; c++) {
sum = sum + votes[c]; // huh? [ ]?
}
return sum;
}

HowtoDeclareanarray(Step1)
Create the array variable (with the name and type)
Make a named ‘list’ with the following parts:
Type Square Braces Array name semicolon
int [ ] arrayOfInts ;
You are ‘declaring’ that
There is an array named arrayOfInts
The elements inside are of type int
You have not (YET) declared how many are in inside
Other Rules:
Arrays can be declared anywhere you can declare a
variable
Do not use ‘reserved’ words or already used names

HowtoCreateanarray(Step2)
Reserve memory for all of the elements in the list:
Array name Keyword Type Size semicolon
arrayOfInts = new int [42] ;
You are reserving memory for:
The array named arrayOfInts
Needs storage for [42]
elements the size of type int
Now you (and the compiler) know how many are in
inside
You cannot change the size after you declare it!
arrayOfInts
[0] [1] [2] [3] [4] … [41]
int int int int int int

TwoStepsononeline:
Declare and Create at the same time:
Type Braces Array name Keyword Type Size semi
int [] arrayOfInts = new int [42] ;
You are ‘declaring’ that
There is an array named arrayOfInts
The elements inside are of type int
You are reserving memory for the array
Needs storage for [42]
elements the size of type int
Note that the size cannot be changed, so you should make
enough room when you start!
79

Exercise: Writethedeclarationsfor:
Declare the array variable (step 1) for these:

Declare the array variable (step 1) for these:
// type [] arrayName ;
int [] arrayOfInts;
float [] hundredFloats;
Zoog [] zoogArmy;

Declare storage (step 2) for the following:

Declare storage (step 2) for the following:
// arrayName = new type[size];
arrayOfInts = new int[30];
hundredFloats = new float[100];
zoogArmy = new Zoog[56];

Both Steps 1 and 2 on the same line:

Both Steps 1 and 2 on the same line:
// type [] arrayName = new type[size];
int [] arrayOfInts = new int[30];
float [] hundredFloats = new float[100];
Zoog [] zoogArmy = new Zoog[56];

Exercise: What’swrongwiththese?
May be valid, maybe not!

87
InitializinganArray
The ‘long’ way
int [] stuff = new int[3];
stuff[0] = 8;
stuff[1] = 3;
stuff[2] = 1;
The one-liner way:
int [] stuff = { 8, 3, 1 };
The compiler counts the number of elements (3)
Sets the size automatically!
Fills the contents with the values inside the { };
Values are separated by commas

InitializingwithIteration
Rolling 5 dice (Yahtzee) Example
The ‘hard’ way
int[] die = new int[5];
=
=
=
=
=
(int)random(0,6);
(int)random(0,6);
(int)random(0,6);
(int)random(0,6);
(int)random(0,6);
die[0]
die[1]
die[2]
die[3]
die[4]
Using a while loop:
int n = 0;
while (n < 5) {
die[n] = random(0,6);
n = n + 1;
}

InitializingwithIteration
Rolling 5 dice (Yahtzee) Example
The ‘hard’ way
int[] die = new int[5];
die[0]
die[1]
die[2]
die[3]
die[4]
=
=
=
=
=
(int)random(0,6);
(int)random(0,6);
(int)random(0,6);
(int)random(0,6);
(int)random(0,6);
Using a for loop:
for (int n = 0; n < 5; n++ ) {
die[n] = (int)random(0,6);
}

Exercise: Loop/Arrayexample:
Using a for loop to initialize an array:
float[] values = new float[6];
for (int i = 0; i < values.length; i++)
values[i] = 0;
Note the use of values.length
The array knows how long it is!
Now write code to square each entry:
int [] nums = { 5, 4, 2, 7, 6, 8, 5, 2, 6, 14 };

Exercise: Loop/Arraycontinued:
int [] nums = { 5, 4, 2, 7, 6, 8, 5, 2, 6, 14 };

Walkingofftheendofthearray…
A very common problem is trying to access an
element in the array that doesn’t exist:
int[] xpos = new int[10];
Remember that we start at element 0
What is the index of the last element? ______
What happens if we try to access element [10]?
for (int i = 0; i <= 10; i++ ) {
xpos[i] = 0;
}
Exception in thread "Animation Thread"
java.lang.ArrayIndexOutOfBoundsException: 10

ArraysLab: PreliminarytoTheSnake
Declare and initialize two ‘global’ arrays:
int[] xpos = new int[10];
int[] ypos = new int[10];
Initialize them in setup()
for (int i = 0; i < xpos.length; i++ ) {
xpos[i] = 0;
ypos[i] = 0;
}
Each time the mouse is clicked, store the
mouseX and mouseY into the next available spot
in the array (fill from left to right)
Each time through draw, display a line between
each location saved in the array.

AdditionalProcessingArrayfeatures
Processing provides a set of functions to help
manage arrays (covered in 9.9):
shorten()
concat() -- Puts two arrays together
subset()
append()
splice()
expand() – Make an array larger in size!
sort() – Sort all the elements in the array
reverse() – Reverse the order of all elements

ArraysofObjects
Using arrays to store multiple objects is a
very powerful programming feature
We will use the Car class (from Chapter 8),
and create a screen full of unique cars

The‘Car’ClassRevisited
class Car { // Define a class below the rest of the program.
color c; // Variables.
float xpos, ypos, xspeed;
// Constructor with three parameters
Car(color c_, float xpos_, float ypos_, float xspeed_) {
c = c_;
xpos = xpos_;
ypos = ypos_;
xspeed = xspeed_;
}
void display() { // Function.
// The car is just a square
rectMode(CENTER);
stroke(0);
fill(c);
rect(xpos,ypos,20,10);
}
void move() { // Function.
xpos = xpos + xspeed;
if (xpos > width) {
xpos = 0;
}
}
}

Maketheparkinglot…
Step 1: Make the reference to the lot
Type Square Braces Array name semicolon
Car [ ] lot ;
Step 2: Make the parking spots
Array name
lot =
Keyword
new
Type
Car
Size
[100]
semicolon
;
Or the ‘one-liner’ version
Type [ ] Array name Keyword Type[Size] semi
Car [ ] lot = new Car[100] ;
lot
[0]
empty
[1]
empty
[2]
empty
[3]
empty
[4]
empty
[5]
empty

NowLet’splayGeneralMotors!
Use a loop to fill up the parking lot!
void setup() {
size(200,200);
smooth();
for (int i = 0; i < lot.length; i ++ ) {
lot[i] = new Car(color(i*2),0,i*2,i/20.0);
}
}
lot
[0]
Car
color
xpos
ypos
xspeed
[1]
Car
color
xpos
ypos
xspeed
[2]
Car
color
xpos
ypos
xspeed
[3]
Car
color
xpos
ypos
xspeed
[4]
Car
color
xpos
ypos
xspeed
[5]
Car
color
xpos
ypos
xspeed

Andlet’sgetthemontheroad!
Use a loop to move and display them!
void draw() {
background(255);
for (int i = 0; i < cars.length; i ++ ) {
cars[i].move();
cars[i].display();
}
}

Section 5
运行控制

A B Output
0 0 0
0 1 0
1 0 0
1 1 1
A B Output
0 0 0
0 1 1
1 0 1
1 1 1
WhatisaBooleanExpression?
Something that resolves to either
true or false (yes or no)
Not maybe…
Computers think in 1’s and 0’s
Remember truth tables
1 = ON = True
0 = OFF = False
Usually based on a comparison
Are you 21 years old?
Is changeCount less than 5?
Is myScore between 80 and 89?
Is lastName ‘Smith’?
AND
OR

BooleanComparisonOperators
Similar to Algebra
>
<
>=
<=
==
greater than
less than
greater than or equal to
less than or equal to
eqality (equal to)
Note: ‘=‘ is the ‘assignment’ operator: x = 5;
!= inequality (not equal to)

BooleanExpressionsandif
What is a Boolean Expression?
A comparison that results in either a true or a false
Where do I use it?
Usually in parenthesis, after an if:
if (age >= 21)
// True Action
if (mouseX < width/2)
// True Action
Only do ‘Action’ if condition is
True
True
Action
Condition
False

Two-wayconditionals: if else
Use else for ‘false’ actions after an if test:
‘Binds’ with the closest if:
if (age >= 21)
// True Action
else // age < 21
// False Action
Take one of the two paths:
True or False
Good idea to use curly braces:
if (age >= 21){
// True Action
} else {
// False Action
}
True
Action
Condition
True
False
False
Action

105
MultipleActions
What if I have more than one thing to do if true?
Make a ‘block’ of code after the if:
if (age >= 21) {
// True Action 1
// True Action 2
} else
// False Action
Indentation is for humans
if (age >= 21)
// True Action 1
// True Action 2
Without the curly braces:
Only the first statement after a conditional is executed
True Action 2 is executed no matter what age is!
And don’t forget to ‘match’ your curly braces!
True
Condition
False
False
Action
True
Action 1
True
Action 2

Multiple-WayBranching: else if
What if you want more than two paths?
Use else if:
if (age >= 21)
// First True Action
else if (age > 18)
// Second True Action
else if (age > 5)
// Third True Action
Only one action done
Then go to the ‘bottom’
First True
Action
Second
True
Action
First
Condition
False
Second
Condition
False
True
True
Third True
Action
True
Third
Condition
False

else if with else attheend
Two ‘true’ paths and one ‘neither’ path?
Use else if:
if (age >= 21)
// First True Action
else if (age > 18)
// Second True Action
else
// Both False Action
First True
Action
Second
True
Action
First
Condition
False
Second
Condition
False
True
True
Both False
Action

ExampleofMulti-wayBranching
Where the mouse is determines the
background color
if (mouseX < width/3) {
background(255);
} else if (mouseX < 2*width/3) {
background(127);
} else {
background(0);
}

Multi-wayBranching: Whichtotestfirst?

GradebookApplication
Determine the letter grade for a number 0-100
90 – 100: A
80 – 89.999 B
70 – 79.999 C
60 – 69.999 D
Below 60: F
How would you plan/code a solution?
What would you test for first?
What second?
How many tests do you need?

NumericRangetesting
You often have to determine if a number is in
a specific range (min to max)
Example: Which range is a number in?
0-25: Print “Young”
26-50: Print “Mid-Age”
>50: Print “Mature”
How would you plan/code a solution?
What would you test for first?
What second?
Can this be done with only two tests?

if else Examples
112
float r = 150; // variables
float g = 0;
float b = 0;
void setup() {
size(200,200);
}
void draw() {
background(r,g,b);
stroke(255); // Line down center
line(width/2, 0, width/2, height);
if (mouseX > width/2)
r = r + 1;
else
r = r - 1;
// If right
// more red
// Else left
// less red
// Range Check r
// Range Check r
if (r
r =
if (r
r =
> 255)
255;
< 0)
0;
}
else ‘binds’ with closest if
You can use if with no else clause!

Rangecheckwithconstrain( )
float g = 0;
float b = 0;
void setup() {
size(200,200);
}
void draw() {
background(r,g,b);
stroke(255); // Line down center
line(width/2, 0, width/2, height);
if (mouseX > width/2)
r = r + 1;
else
r = r - 1;
// If right
// more red
// Else left
// less red
r = constrain(r,0,255); // Range Check r
}

Three-waybranching
114
float g = 0;
float b = 0;
void setup() {
size(200,200);
}
void draw() {
background(r,g,b);
stroke(255);
line(width * 2/3, 0, width * 2/3, height);
line(width * 1/3, 0, width * 1/3, height);
if (mouseX > (width * 2/3)) // right 3rd
r = r + 1;
else if (mouseX < (width * 1/3)) // left 3rd
r = r -1;
else // center 3rd
ellipse(mouseX, mouseY, 30,30);
r = constrain(r,0,255); // Range Check r
}

115
Exercise: Movearectangle…butstop!
float x = 0;
void setup() {
size(200,200);
}
void draw() {
background(255);
fill(0);
rect(x,100,20,20);
x = x + 1;
// Keep x in left half
// Conditional version:
// constrain version:
}

A B Output
0 0 0
0 1 0
1 0 0
1 1 1
LogicalOperators: AND
Sometimes two (or more) things need to be true
before you want to do something
Example:
If age >= 16 AND permit == 1
Print “OK to drive”
How do we spell ‘AND’? &&
‘Nested ifs:’
int age = 17;
int permit = 1;
if (age >= 16)
if (permit == 1)
print(“OK to Drive”);
else
print(“Ride the bus”);
else
One if, compound condition
int age = 17;
int permit= 1;
if (age >= 16 && permit == 1)
else
Remember: else ‘binds’ with closest if
(without an else)

A B Output
0 0 0
0 1 1
1 0 1
1 1 1
LogicalOperators: OR
Sometimes one of (two or more) things is
enough to decide
int age = 17;
int permit = 1;
if (age >= 18 || (age >= 16 && permit == 1))
else
Example:
If age >= 18 OR (age >= 16 AND permit == 1)
How do we spell ‘OR’? || (two vertical bars)

LogicalOperators: OR
Sometimes one of (two or more) things is
enough to decide
Example:
If age >= 18 OR (age >= 16 AND permit == 1)
How do we spell ‘OR’? || (two vertical bars)
int age = 17;
int permit = 1;
if (age >= 18 || (age >= 16 && permit == 1))
else
Note the use of parenthesis to ‘connect’ the AND clause

Exercise: SimpleRollover
119
int
int
int
int
x
y
w
h
=
=
=
=
50;
50;
100;
75;
void setup() {
size(200,200);
}
void draw() {
background(255);
stroke(255);
// test if mouse is over the rectangle
if ( mouseX.. && mouseY.. && ???
// Change the color of the rectangle
rect(x,y,w,h);
}

booleanvariables
You may want to ‘remember’ if something is true
or false and store it in a variable
Then you can compare it to true or false
Example:
If age >= 16 AND permit == true
int age = 17;
boolean permit = true;
if (age >= 16 && permit == true)
else

Usinga boolean variableforButtons
A button is just a rollover area that senses
mouse clicks.
Testing if (mouse is in the area of the object) AND
mouse clicked can be quite a number of comparisons!
boolean button = false;
int ulx = 50, uly = 50, w = 100, h = 75; // rect variables
…
if (mouseX > ulx && mouseY > uly &&
mouseX < ulx + w && mouseY < uly + h &&
mousePressed)
button = true;
else
button = false;
// Later in code
if (button == true)
print(“I’ve been clicked!”);

mouse clicks.
…
mousePressed)
button = true;
else
button = false;
// Later in code
if(button) == true) Does the same thing as if (button == true)
//

//
mouse clicks.
…
mousePressed)
button = true;
else
button = false;
// Later in code
if(button) == true) Does the same thing as if (button == true)
Do you like the way the tests are lined up on multiple lines?

Example: AButtonasaswitch
Test where the mouse is in the mousePressed()
method.
Then set a boolean variable to true or false
…
void draw() {
if (button)
// actions if button pressed
}
void mousePressed() {
mouseX < ulx + w && mouseY < uly + h)
if (button) // alternate on every click
button = false;
else
button = true;
}

button = false;
else
button = true;
Example: AButtonasaswitch
Test where the mouse is in the mousePressed()
method.
Then set a boolean variable to true or false
…
void draw() {
if (button)
// actions if button pressed
}
mouseX < ulx + w && mouseY < uly + h)
if (button) !button; // alternate on every shorter, eh?
= a // quite bit click
}
}

Use a boolean
variable to represent if
we are moving or not.
Change the variable
each time the mouse
pressed.
126
Exercise: Clicktostartamoving‘ball’
// Declare a boolean, set to false
int circleX = 0;
int circleY = 100;
void setup() {
size(200,200);
}
void draw() {
background(100);
stroke(255);
fill(0);
ellipse(circleX, circleY, 50, 50);
// Move the circle only after a click
}
// react to the mouse being pressed
// Location of the mouse doesn’t matter
}

Use a variable speed
which can be positive
or negative.
Change speed to
negative if we bounce
off the right edge.
127
Example: Abouncing‘ball’
int circleX = 0;
int speed = 1;
void setup() {
size(200,200);
smooth();
}
void draw() {
background(255);
circleX = circleX + speed;
if ( circleX > width || circleX < 0)
speed = speed * -1; // reverse course
// Display the circle at x location
stroke(0);
fill(175);
ellipse(circleX, 100, 32, 32);
}
// What will this do?
speed = speed + 1;
}

You can print the
variable speed to see
what it is doing.
Use println(speed)
if you want one number
per line.
128
Anoteaboutdebugging…
int circleX = 0;
int speed = 1;
void setup() {
size(200,200);
smooth();
}
void draw() {
background(255);
circleX = circleX + speed;
if ( circleX > width || circleX < 0)
speed = speed * -1; // reverse course
// Display the circle at x location
stroke(0);
fill(175);
ellipse(circleX, 100, 32, 32);
}
speed = speed + 1;
println(speed);
}

Section 6
循环控制

130
WhyuseIteration?
Without Iteration:
// No variables
stroke(0);
line( 50,60, 50,80);
line( 60,60, 60,80);
line( 70,60, 70,80);
line( 80,60, 80,80);
line( 90,60, 90,80);
line(100,60,100,80);
line(110,60,110,80);
line(120,60,120,80);
line(130,60,130,80);
line(140,60,140,80);
line(150,60,150,80);

WhyuseIteration?
Without Iteration:
// No variables
stroke(0);
line( 50,60, 50,80);
line( 60,60, 60,80);
line( 70,60, 70,80);
line( 80,60, 80,80);
line( 90,60, 90,80);
line(100,60,100,80);
line(110,60,110,80);
line(120,60,120,80);
line(130,60,130,80);
line(140,60,140,80);
line(150,60,150,80);
Study what changes
x’s increase each time
What is the pattern?
Add 10 each time
When does it stop?
Last line is at x = 150

// With x variable
int x = 50;
int spacing = 10;
int len = 20;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
..
132
PlanningIteration(Step1)
Without Iteration:
// No variables
stroke(0);
line( 50,60, 50,80);
line( 60,60, 60,80);
line( 70,60, 70,80);
line( 80,60, 80,80);
line( 90,60, 90,80);
line(100,60,100,80);
line(110,60,110,80);
line(120,60,120,80);
line(130,60,130,80);
line(140,60,140,80);
line(150,60,150,80);

PlanningIteration(2)
Find the repetitive code
// With x variable
int x = 50;
int spacing = 10;
int len = 20;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
..
133

PlanningIteration(3)
Plan the ‘exit’ condition
When to stop drawing lines
x == 150?
x > 150?
x < 150?
x <= 150?
x >= 150?
// With x variable
int x = 50;
int spacing = 10;
int len = 20;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
..
134

135
Action(s)
Condition
TheonlyLoopYouReallyNeed: while
Use a Boolean Expression to test if we are done
Just like in if-else
True
False
There are there other types loops available:
do-while
for

Howtoplanaloop:
Three Parts in every loop:
Setup variables
Test Condition
Change test variable
Action(s)
Change test
variable
136
True
Test
Condition
False
Make sure the loop will end!
The condition should be false at some point…
Or you have an ‘infinite’ loop! (not good)
Setup

LegsusingIteration
Use the same ‘setup’
Put the repetitive code
inside the loop
Put your exit condition
in the ‘test’
// Loop Version
int x = 50;
int spacing = 10;
int endLegs = 150;
while(x < endLegs) {
line(x,60,x,80);
x = x + spacing;
}
// With x variable
int x = 50;
int spacing = 10;
int len = 20;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
x = x + spacing;
line(x,60,x,80);
..

Setup
Test
Change
ThreePartsoftheLoop
Find the three parts:
// Loop Version
int x = 50;
int spacing = 10;
int endLegs = 150;
while(x < endLegs) {
line(x,60,x,80);
x = x + spacing;
}

Let’sseeifwecanplanandwritealoop…
Look at Figure 6.5
Use 200 x 200 grid
What changes per bar?
Plan the three parts:
Setup (initial condition)
Initial y (top bar) ___
Last y: ________
Test (when to stop)
___________
Change
How far apart are bars?
___________
Plan the width too
How wide are they? _____
Where to start? x = _____
Note: x doesn’t change!
139

GraphPapertotheRescue!
50 60 70

141
Andthecodefortheloop‘fallsout’…
void setup() {
size(200,200);
background(255);
fill(125);
}
void draw() {
int y = 5;
int last = height;
while(y < last) {
rect(50,y,100,10);
y = y + 20;
}
}

Exercise:

ExitConditions: Whentostop!
How do we know when to stop?
Test is usually based on a comparison with a variable
Until age is 21
While changeCount is greater than 5
While not done
Until hitSomething is true
While dayOfMonth is less than daysInMonth
What if we don’t stop?
You probably forgot to change the test variable!
Or you changed it in the wrong direction
You have written an ‘infinite’ loop
Not good. Must ‘kill’ processing to get out!
143

144
Yournextloop: for
Use a for loop when:
1) Your ‘test’ variable is a number
2) You know when to stop before you start
Put all three parts on one line:
for(Setup variables;Test Condition;Change test variable){
// Action(s) go here
}
Action(s)
Change test
variable
Test
Condition
True
False
Setup

145
for loopSyntaxandExample
Use two semicolons (;) as separators:
for(Setup variables;Test Condition;Change test variable){
for( int x = 1; x < 10 ; x = x + 1) {
// Action(s) go here
}
Who came up with this?
Programmers of course
Why?
It saves typing, and it puts all three parts on one line

Exercise: Whiletoforloop

Exercise
WuzzitDo?
for (int i = 0; i < 10; i++) {
rect(i*20,height/2, 5, 5);
}
int i = 0;
while (i < 10) {
ellipse(width/2,height/2, i*10, i*20);
i++;
} for (float i = 1.0; i < width; i *= 1.1) {
rect(0,i,i,i*2);
}
int x = 0;
for (int c = 255; c > 0; c –= 15) {
fill(c);
rect(x,height/2,10,10);
x = x + 10;
}

// Global " count "
int count = 0;
void setup() {
size(200,200);
}
void draw() {
count = count + 1;
background(count);
}
________
// Local " count "
void setup() {
size(200,200);
}
void draw() {
int count = 0;
count = count + 1;
background(count);
}
________
Example
Global versus Local variables in loops
Which will these produce? A, B or C?

for LoopVariable‘BlockScope’
for( int x = 1; x < 10; x = x + 1) {
// steps to do inside the loop
// You can use ‘x’ anywhere in this box
}
if (x > 100) // but x is gone now!
Scope is the ‘lifetime’ of a variable.
When ‘x’is declared in the for statement:
‘x’ exists only inside the ‘block’ of the for loop { }
Do you have to declare x inside the for loop? NO
int x; // Declare before loop starts (local scope)
for( x = 1; x < 10; x = x + 1) { // assign here

LoopInsidetheMainLoop
Remember that draw()is called in a ‘loop’
This is often called the ‘main’ loop
The last thing that draw()does is.. .
(remember Chapter 1?) ….. Paints the screen
How could you make a set of parallel
horizontal lines on the screen?

Exercise
Render one line at a time inside a for loop:
Until the reach the bottom

MarchingLinesPlan
Use a global variable to remember where on the
Y axis to start each time (between 1 and 20)
0, 1, 2, 3…. 19, 0, 1, 2, 3…
Initialize it 0
Every time through draw()
1) Clear the screen
2) Draw a set of parallel lines (20 pixels apart)
Starting at the Y axis where the global variable tells us to
Add 20 to the Y axis each time through
Loop until Y is >= the height of the screen
3) Increment the global variable by 1
If it reaches 20, set it back to 0

ShuttersPlan(whatchanged?)
Use a global variable to remember where on the
Y axis to start each time (between 1 and 20)
0, 1, 2, 3…. 19, 0, 1, 2, 3…
Initialize it 0
Every time through draw()
1) Draw a set of parallel lines (20 pixels apart)
Starting at Y axis where the global variable tells us to
Add 20 to the Y axis each time through
Loop until Y is >= the height of the screen
2) Increment the global variable by 1
If it reaches 20, set it back to 0 and…
Clear the screen

IncrementandDecrementOperators
Loops often use a counter and increment or decrement it
as they go.
Here is a a “shortcut” way to decrement or increment a
variable:
increment operator
++x;
x++;
// increments x by one – BEFORE it is used
// increments x by one – AFTER it is used
decrement operator
--x;
x--;
// decrements x by one – BEFORE it is used
// decrements x by one – AFTER it is used
• When these operators are used as part of an expression,
then the choice of pre versus post will make a difference.

Howtomeasuredistancebetweenpoints
Take one axis (X) for example:
float distance = abs(mouseX – i);
abs() function returns a positive number
Absolute value… remember algebra!
Used in example 6.9
Exercise 6.6:
Rewrite 6.9 using a for loop

Section 7
函数

Modularity
What is a function?
A named block of code
Sometimes called a ‘module’, ‘method’ or a ‘procedure’
Some examples that you know are:
setup()
draw()
mousePressed()
background()
ellipse()
rect()
In pseudocode, they might be‘high-level’ headings:
Erase background
Draw Spaceship
Draw enemies
Move spaceship based on user keyboard command
Move enemies

Erase background
Draw Spaceship
Draw enemies
Move spaceship
Get keyboard command
Move spaceship
Move enemies
Some functions are ‘built-in’
You can write your own!
PseudocodetoFunctions
// Modularized draw()
Each time through draw: void draw() {
background(0);
drawSpaceShip();
drawEmenies();
moveShip();
moveEnemies();
}

Whyusefunctions?
Is your draw()method getting a bit long?
Two key principles of good programming:
1) Modularity
Break down code into smaller parts
More manageable and readable
Reduce the number of local variables inside a module
2) Reusability
Duplicated code (copy/paste?) is not good
Must maintain in multiple places
Better to put duplicate code in a new function and ‘call’ it from
multiple places

Exercise: Modular‘Pong’Planning
What functions might be used in the game of pong?
1) Decide on the ‘rules’
One player or two player?
One player example
Two player example
2) Write Pong pseudocode (or flow chart)
3) Decide on function names
For user-defined functions
4) Think about variables you will need
Local (inside a function) or ‘global’?
Create names you can remember

TheFunction‘Definition’
Make a named ‘block’ with the following parts:
Return type
void
Function name Parameters area start block
drawShip ( ) {
// Variables and code go here
} // end drawShip
This is also called ‘declaring’ the function
You are ‘telling’ the compiler that there is a new
named block of code and how it works
Other Rules:
Define function outside all other functions
Name with the same rules as variables (letters, digits, _)
Do not use ‘reserved’ words or already used names

CallingaFunction
Now that we have a function, let’s use it:
void draw() {
drawShip(); // note the semicolon!
}
You ‘Call’ functions from ‘inside’ other functions
In this case, inside draw()
You call functions by using the function name:
Return type Function name Arguments area semicolon
<empty> drawShip ( ) ;

Exercise: Writeandcallafunction
Display a multi-part graphic (or a Zoog!)

BouncingBallwithoutFunctions
Group code into related ‘chunks’

BouncingBallwithFunctions
Name the ‘chunks’, declare functions, call them!

FunctionswithArgumentsandParameters
What if you wanted to use a function to do
slightly different things?
Some examples you have seen that pass
arguments to functions include:
size(200,200);
color(100,150,0);
ellipse(x, y, width, height);
More?
What if you wanted to write your own function
that receives parameters?

ArgumentsandParameters
Wikipedia Reference:
http://en.wikipedia.org/wiki/Parameter_(computer_science)
The book (and many professionals) confuse the
two words.
Per most texts and Wikipedia:
Arguments are ‘sent’
Parameters are ‘received’
167
// drawBlackCircle receives size parameter
void drawBlackCircle(int diameter) {
fill(0);
// passes arguments to ellipse()
ellipse(50, 50, diameter, diameter);
}
Argument comes before
Parameter

168
Multiple
Arguments
void draw() {
background(0);
// Pass drawCar four
drawCar( 100,100,64,
drawCar( 50 ,75 ,32,
arguments
color(200,200,0) );
color(0,200,100) );
drawCar( 80 ,175,40, color(200,0,0) );
}
// drawCar receives four parameters
void drawCar(int x, int y, int thesize, color c) {
// Using a local variable "offset"
int offset = thesize/4;
// Draw main car body
…
}

169
PassingVariables
void draw() {
background(0);
int size = 32;
// Pass drawCar four arguments
drawCar( 100,100,size, color(200,200,0) );
size = size + 16;
drawCar( 50 ,75 ,size, color(0,200,100) );
size = size + 16;
drawCar( 80 ,175,size, color(200,0,0) );
}
// drawCar receives four parameters
void drawCar(int x, int y, int thesize, color c) {
// Using a local variable "offset"
int offset = thesize/4;
// Draw main car body
…
}

KeystoPassingArguments
You must pass the same number of arguments as defined
in the function parameter list.
When an argument is passed, it must be of the same type
as declared within the parameters in the function definition.
An integer must be passed into an integer
a floating point into a floating point..
The value you pass as an argument to a function can be a:
Literal value (20, 5, 4.3, etc.),
Variable (x, y, size, etc.)
The result of an expression (8 + 3, 4 * x/2, random(0,10), etc.)
Parameters act as local variables inside the receiving
function
They are only accessible within that function

Exercise: Writeafunctiondefinition:
void draw() {
float curHourly = 12.25;
float raisePct = 9.0;
showNewHourly(curHourly, raisePct);
}
// Make a comment line above the name
// return type function name ( parameters ) {
// Indented code goes here
// Print the new hourly rate
}
Write your own showNewHourly()function
definition to match the function call

Exercise: BouncingCar
int globalX = 0;
int globalY = 100;
int speed = 1;
void draw() {
background(0);
// Call move
// Call bounce
// Call drawCar with global X and Y and other params;
}
Write your own function calls to match the
functions move, bounce and drawCar

WhatamIreallypassing?
Can the receiving function change the variable
that you pass?
That might be… dangerous…
Here are the rules in Processing and Java:
All primitive types (int, float, double, char…) are
passed by copying the contents of the variable inside
the argument into the new parameter variable.

174
PassbyValue(Animated)
Let's take a closer look at how this works.
void draw() {
RAM
n
num
int n = 10;
println(n);
byValue(n);
println(n);
} // end draw()
10
void byValue(int num) {
num = 73;
println(n);
} // end byValue()
10
10
73

WuzzitDo?

Returntypes
Up until now, you have used a mysterious
keyword named void before all of your functions
void
void
void
void
setup() {
draw() {
byValue(int num) {
drawCar(int x, int y, int thesize, color c) {
Remember the parts of a function definition?
Return type
void
Function name Parameters area start block
drawShip ( ) {
Here is an example that ‘return’ an int:
int sum(int a, int b, int c) {
int total = a + b + c;
return total; // Return a copy of a local variable
}

177
Assigningthereturnvaluetoavariable
draw calls sum with arguments
sum receives values into parameters
sum method calculates local total
sum method returns copy of total
draw assigns returned val to answer
void draw() {
int answer;
answer = sum( 17, 42, 52);
println(answer);
noLoop();
}
int sum(int a, int b, int c) {
int total = a + b + c;
return total;
}

178
Ausefulexample: Distancebetween2pts
float distance(float x1, float y1, float x2, float y2) {
float dx = x1 – x2; // one side of the right triangle
float dy = y1 – y2; // other side of the right triangle
// hypoteneuse length
float d = sqrt(dx*dx + dy*dy);
return d;
}
Processing has a dist()function that does the same thing…

Section 8
面向对象编程

ObjectOrientedProgramming(OOP)
OOP is a different way to view programming
Models the real world
A different view than ‘Structured’ programming
Functions break a program into ‘modules’ like an outline
What is an Object?
Usually based on a ‘noun’
It has ‘properties’
It has ‘actions’ (methods) that it can do (verbs)
An examples of an object that you know:
String
The dot operator is used to make the String do work!

WhyObjects?
OOP allows you to put data about something
and actions it can do together into one
“object”
OOP has been around since the 1960s
Most popular current languages have either
adapted or were designed with OOP
C  C++  C#
JavaScript
Java

ObjectExample: Human
Attributes
Age
Height
Weight
Name
Eye color
Hair color
…
Functions
Sleep
Wake-Up
Eat
Ride something

ClassesandObjects
A Class
A ‘plan’ for an object: Cookie Cutter
The general idea of a thing
Has placeholders for details, but not ‘made’ yet
It declares functions that could be done to an object
An Object
An ‘instance’ of a Class: A Cookie
A ‘real’ thing that has all of the specifics
It can be ‘told’ to execute it’s functions
You have to have a ‘plan’ before you can make an
object:
Class beforeObject

Exercise: PlanaCarClass
Let’s plan a simple Car
List data and functions
Let’s compare how we could convert the function
we wrote to show different card with objects
We’ll use our setup() and draw() methods

Setupfora‘Car’beforeObjects
Use global variables for ‘properties’
Color:
Location:
Speed:
carColor
carX, carY
carSpeed
In setup()
Set the carColor
Set the starting location
Set the initial speed
In draw()
Fill background
Display car at location with color (may use a function)
Increment car’s location based on speed

186
Setupmultiple‘Cars’beforeObjects
Use global arrays of variables for ‘properties’
Allows us to use a loop to initialize a number of Cars
Declare Color array: carColor [ ]
Declare carX array:
Declare carY array:
carX [ ]
carY [ ]
Declare carSpeed array: carSpeed [ ]
In setup()
Set and initialize the arrays
In draw()
Fill background
Loop through all the cars
Display car at location with color (may use a function)
Increment car’s location based on speed

Setupa‘Car’usingObjects
One big difference with objects is that you move
all of the global variables inside the Car object
Color:
Location:
Speed:
carColor
carX, carY
carSpeed
Car object instead!
We end up with one variable to
represent the car
Instead of initializing all of those
variables, we initialize the car
object!

Setupa‘Car’usingObjects
Outside of all methods (global)
Declare a ‘parking place’ for a car
In setup()
Make a new car object
based on the ‘Car’ plan)
Sets initial values for color, location and
speed
In draw()
Fill background
Tell the car to ‘move’ based on speed
Tell the car to ‘display’ itself (call a
function)

The‘Car’class
Convert the non-OOP Car Data to a Class
Non-OOP OOP

Setupa‘Car’usingObjects-Data
Let’s break it down step by step
Declare the plan for the ‘Car’
Outside draw() and setup()
Put variables for color, location and speed inside

Setupa‘Car’usingObjects-Constructor
We need to write instructions to build a car
It is called the ‘Constructor’ method
Move the code that was in setup()
Set variables for color, location and speed inside

Setupa‘Car’usingObjects-Functions
Move the functions that did things to the car
Move the code to inside the Car class
The will be called methods of the class
Move the code that was in display()and drive()

Thewhole‘Car’(Example8.1)
class Car { // Define a class for a car
color c; // Variables.
float xpos;
float ypos;
float xspeed;
Car() { // A constructor.
c = color(175);
xpos = width/2;
ypos = height/2;
xspeed = 1;
}
void display() { // Function.
// The car is just a square
rectMode(CENTER);
stroke(0);
fill(c);
rect(xpos,ypos,20,10);
}
void drive() { // Function.
xpos = xpos + xspeed;
if (xpos > width) {
xpos = 0;
}
}
}

class Car {
Car() { // Constructor
c = color(175);
xpos = width/2;
ypos = height/2;
xspeed = 1;
}
Whatwasthatabouta‘Constructor’?
A constructor is a special method of a class
Has the same name as the class
“Builds’ the object
Sets initial values
It is ‘called’ with you use new:
void setup() {
size(200,200);
// Initialize Car object
myCar = new Car();
}

AndhereistheOOPizedversion
Is the OOP version shorter?
Is it easier to read?
Not yet maybe, but soon, and for the rest of your
life.

CarClassshouldreallybeinitsownfile…
Click ‘Right Arrow’ in tabs row
Use ‘New Tab’ in menu to create a new file
Name the new tab exactly like the class = ‘Car’
Move the code for the ‘Car’ class to it
Saves to a ‘Car.pde’ file in your folder
Keep both files in the same folder
If you want to use your ‘Car’ class in another
project, simply copy the ‘Car.pde’ file there

Whatifwewanttomakemorecars?
Right now, all cars are exactly the same
Their constructor sets up the color, location…
How could we make ‘custom’ cars?
Remember parameters?
What if a Car constructor took parameters?
class Car {
Car(color colp, int xp, int yp, int speedp) {
c = colp;
xpos = xp;
ypos = yp;
xspeed = speedp;
}

Pleasereviewparameterpassing…
Make a new frog with a length of 100

Nowwecanmaketwo‘custom’cars
Use your new ‘parameterized’ constructor!

AndimagineanarrayofCars!
You can use the ‘Car’ class just like any other type
Declare an array of our new Cars object:
Car [ ] parkingLot;
setup() {
parkingLot = new Car[10];
}
But wait… what just happened?
Did you create 10 cars? No, not yet.
You created 10 parking stalls for cars
So we still have to ‘build’ the cars and set all of the
colors, locations and speeds…
parkingLot[0] = new Car(color, x, y..);

Fillingtheparkinglottheeasyway!
Once you have the parking lot created,
Car [ ] parkingLot;
setup() {
parkingLot = new Car[10];
}
Use a for loop to make a bunch of cars!
for (int i; i < 10; i++) {
parkingLot[i] = new Car(color, x, y..);
}
Arrays and loops work wonderfully together!
And they are even more fun with objects!

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