Lecture on graphics

Computer Graphics
 Computer Graphics is one of the most
powerful and interesting aspect of
computers. There are many things we can
do in graphics apart from drawing figures
of various shapes.
 All video games, animation, multimedia
predominantly works using computer
graphics.

Graphics in C
 There is a large number of functions in C which
are used for putting pixel on a graphic screen to
form lines, shapes and patterns.
 The Default output mode of C language
programs is “Text” mode. We have to switch to
“Graphic” mode before drawing any graphical
shape like line, rectangle, circle etc.

Basic color Function

 textcolor() function
 textbackground() function
 setbkcolor() function
 setcolor() function

textcolor() function
Declaration:
void textcolor( newcolor);
Remarks:
 This function works for functions that produce text-
mode output directly to
the screen (console output functions).
 textcolor selects a new character color in text
mode.
 This functions does not affect any characters
currently on the screen.

textbackground() function
Declaration:
void textbackground( newcolor);
Remarks:
textbackground selects the background color for text mode.
If you use symbolic color constants, the following limitation
apply to the background colors you select:
 You can only select one of the first eight colors (0--7).
NOTE: If you use the symbolic color constants, you must
include conio.h.

setcolor() function
Declaration:
void setcolor(color);
Remarks:
setcolor sets the current drawing color to color,
which can range from 0 to getmaxcolor.

setbkcolor() function
Declaration:
void setbkcolor(color);

Remarks:
setbkcolor sets the background to the color
specified by color.

Example 1.
txtcolor() & textbackground() functions
#include<graphics.h>
#include<stdio.h>
#include<conio.h>
Void main()
{
textcolor(4); OR textcolor(4+BLINK)
textbackground(3);
cprintf(“NFC-IEFR INSTITUTE ”);
getch();
}
OUTPUT

NFC-IEFR INSTITUTE

Graphics in C
 There are lot of library functions in C language
which are used to draw different drawing
shapes.
 For eg.
 line(x1, y1, x2, y2);
 putpixel(x, y);
 circle(xCenter, yCenter, radius);
 rectangle(x1, y1, x2, y2);
 ellipse(xCenter, yCenter, start, end, Xradius, Yradius);
 arc(xCenter, yCenter, start, end, radius);

Graphics in C
Example 2
#include<graphics.h>
void main(void)
{
int dr=DETECT, md;
initgraph(&dr,&md,”c:tcbgi”);
line(0 , 0, 640, 480);
getch();
closegraph();
}

Dissecting initgraph(…) Function
 The initgraph function is used to switch the output
from text mode to graphics mode.
 The initgraph function takes three arguments.

initgraph(&dr , &md , ”c:tcbgi” );

graphics Initial Directory path
Driver graphics of graphics
Type mode driver

Graphics Drivers
Constant Value
DETECT 0 (requests auto detection)
CGA 1
MCGA 2
EGA 3
EGA64 4
EGAMONO 5
IBM8514 6
HERCMONO 7

ATT400 8
VGA 9
PC3270 10

Graphics Mode
driver graphics_modes Value Column x Row Colors
CGA CGAC0 0 320 x 200 4 colors
CGAC1 1 320 x 200 4 colors
CGAHI 4 640 x 200 2 colors
EGA EGALO 0 640 x 200 16 colors
EGAHI 1 640 x 350 16 colors
VGA VGALO 0 640 x 200 16 colors
VGAMED 1 640 x 350 16 colors
VGAHI 2 640 x 480 16 colors

Directory path of graphics driver
 The third argument to initgraph() is the pathname for
the graphics drivers. This driver is a file like cga.bgi or
egavga.bgi.
 cga.bgi file is used to run programs in CGA modes.
 egavga.bgi file is used to run programs in EGA or VGA
modes.
 Other Drivers are available for other display standards
such as Hercules and IBM 8514.
 In the current version of Turbo C, these driver files are
located in the subdirectory tcbgi. So this is the
pathname used in the arguments to initgraph().

line() function
 line draws a line between two specified points

Syntax:
line(x1, y1, x2,y2);

Remarks
line draws a line from (x1, y1) to (x2, y2) using
the current color, line style, and thickness.

line() function
 e.g:
line(0, 0, 640, 480);
x=0 x=320 x=640
y=0 y=0

y=240 y=240

y=480 y=480
x=0 x=640

setlinestyle() function
Sets the current line style and width or pattern

Syntax:
setlinestyle (linestyle, upattern, thickness);

Remarks:
setlinestyle sets the style for all lines drawn by line,
lineto, rectangle, drawpoly

Line Styles
Line Style Int Value Pattern
SOLID_LINE 0

DOTTED_LINE 1

CENTER_LINE 2

DASHED_LINE 3

USERBIT_LINE 4 User Defined

upattern, thickness
 U pattern
 User can define its own pattern.
 0 should be used if using predefined pattern,
other wise any integer number representing
user pattern
 Thickness
 Thickness of the line in pixels

rectangle() function
Draws a rectangle (graphics mode)

syntax:
void rectangle(left, top, right, bottom);

Remarks:
 rectangle draws a rectangle in the current line
style, thickness, and drawing color.
 (left,top) is the upper left corner of the rectangle,
and (right,bottom) is its lower right corner.

e.g: rectangle() function
rectangle(10, 10, 200,200);

10, 10

200,200

bar( ) function
bar(..) function Draws a bar
 Syntax:
void bar( left, top, right, bottom);

 Remarks:
 bar draws a filled-in, rectangular, two-dimensional bar.
 The bar is filled using the current fill pattern and fill
color. bar does not outline the bar.
 To draw an outlined two-dimensional bar, use bar3d
with depth = 0.

e.g: bar( ) function
Usage:
bar(10,10,200,200);

10,1
0 fill pattern

200,200

bar3d() function
Declaration:
void bar3d(left,top,right, bottom, depth,topflag);
Remarks:
bar3d draws a three-dimensional rectangular bar, then fills it using the
current fill pattern and fill color. The three-dimensional outline of the bar is
drawn in the current line style and color.

Parameter What It Is/Does
depth Bar's depth in pixels
topflag Governs whether a three-dimensional top is put on the
bar

(left, top) Rectangle's upper left corner

(right, bottom) Rectangle's lower right corner

eg: bar3d() function
Usage:
setfillstyle(4, 4);
bar3d(100, 100, 200, 200, 20, 1);

OUTPUT
100,100

20 (depth)

200,200

circle() function
Declaration:
void circle(x,y,radius);
Remarks:
circle draws a circle in the current drawing color.

Argument What It Is/Does

(x,y) Center point of circle

radius Radius of circle

eg: circle() function
Usage:
circle(320,240,50);

OUTPUT
50 radius in pixels
320,240

arc() function
Declaration:
void arc(x,y,stangle,endangle radius);
Remarks:
arc draws a circular arc in the current drawing color.

(x,y) Center point of arc
stangle Start angle in degrees
endangle End angle in degrees
radius Radius of circle

eg: arc() function
Usage:
arc(320, 240, 0, 270, 50);

OUTPU
T
50 radius in pixels
320,240

0 stangle
270 endangle

ellipese() function
Declaration:
void ellipse(x, y,stangle,endangle,xradius,yradius);
Remarks:
ellipse draws an elliptical arc in the current drawing color.

(x,y) Center point of ellipse
stangle Start angle in degrees
endangle End angle in degrees
xradius H

eg: ellipse() function
Usage:
ellipse(320, 240, 0, 270, 100,50);

50 xradius in pixels
OUTPU
T
50 yradius in pixels
320,240

0 stangle
270 endangle

fillellipse() function
Declaration:
void far fillellipse(x, y,xradius, yradius);
Remarks:
fillellipse draws an ellipse, then fills the ellipse with the
current fill color and fill pattern.


(x,y) Center point of ellipse

xradius Horizontal axis

yradius Vertical axis

e.g: fillellipse() function
Declaration:
void far fillellipse(x, y, xradius, yradius);
Remarks:
fillellipse draws an ellipse, then fills the ellipse with the
current fill color and fill pattern.

Center point of ellipse

xradius Horizontal axis

eg: fillellipse() function
Usage:
setfillstyle(5, 4);
fillellipse(320, 240, 0, 270, 100,50);

OUTPUT

current fill color and fill pattern

e.g: setfillstyle() function
Declaration:
void setfillstyle(pattern, color);
Remarks:
setfillstyle sets the current fill pattern and fill
color.

e.g: setfillstyle() function
Fill patterns

Names Value Means Fill With Pattern
EMPTY_FILL 0 Background color
SOLID_FILL 1 Solid fill
LINE_FILL 2 ---
LTSLASH_FILL 3 ///
SLASH_FILL 4 ///, thick lines
BKSLASH_FILL 5 , thick lines
LTBKSLASH_FILL 6
HATCH_FILL 7 Light hatch
HATCH_FILL 8 Heavy crosshatch
INTERLEAVE_FILL 9 Interleaving lines
WIDE_DOT_FILL 10 Widely spaced dots
CLOSE_DOT_FILL 11 Closely spaced dots
USER_FILL 12 User-defined fill pattern User Defined

putpixel() function
Declaration:
void putpixel(x, y, color);

Remarks:
putpixel plots a point in the color defined by
color at (x,y)

Viewports
 Viewports provide a way to restrict to an arbitrary
size the area of the screen used for drawing. We can
draw an image that would ordinary occupy the
entire screen but if a view port is in use, only part
of the image will be visible.
 The View Ports don’t scale the image; that is, the
image isn’t compressed to fit the view port, Rather,
the parts of the image that don’t fit in the view port
are simply not visible

setviewport() Funciton
Sets the current viewport for graphics output
 Declaration:

void far setviewport(left,top,right,bottom,clip);
 Remarks:
 setviewport establishes a new viewport for graphics output.
 The viewport's corners are given in absolute screen
coordinates by (left,top) and (right,bottom).
 The clip argument determines whether drawings are clipped
(truncated) at the current viewport boundaries. If clip is
non-zero, all drawings will be clipped to the current
viewport.

e.g: setviewport() Function
setviewport(0,0,200,200,1);
rectangle(0,0,200,200);
circle(320,240,250);
ellipse(320,240,0,360,250,100);
OUTPUT:

clearviewport() Function
 Clear the current viewport.
 eg:
circle(320,240,260);
setviewport(0,0,200,200,1);
rectangle(0,0,200,200);
circle(320,240,250);
ellipse(320,240,0,360,250,100);
getch();
clearviewport();

Text with Graphics
 There are functions in C language that draw
text characters in graphics mode. These
functions can be used to mix text and graphics
in the same image. These functions also make
it possible to change text font and very the size
of text.

outtext() function
 outtext displays a string in the viewport (graphics
mode)

 Declaration:
void outtext(far *textstring);
 Remarks:
outtext display a text string, using the current
justification settings and the current font, direction,
and size. outtext outputs textstring at the current
position (CP).

outtextxy() Function
 outtextxy displays a string at the specified location
(graphics mode)
 Declaration:
void outtextxy(x, y, far *textstring);
 Remarks:
outtextxy() display a text string, using the current
justification settings and the current font, direction,
and size.(CP)
outtextxy() displays textstring in the viewport at the
position (x, y)

settextstyle( ) Function
Sets the current text characteristics
 Declaration:
void settextstyle(font, direction, charsize);
 Remarks:
 settextstyle() sets the text font, the direction in which
text is displayed, and the size of the characters.
 A call to settextstyle() affects all text output by outtext
and outtextxy.

 direction
Font directions supported are horizontal text (left
to right) and vertical text (rotated 90 degrees
counterclockwise).
 The default direction is HORIZ_DIR.

Name Value Direction

HORIZ_DIR 0 Left to right

VERT_DIR 1 Bottom to top

 Charsize
 The size of each character can be magnified
using the charsize factor.
 If charsize is non-zero, it can affect bit-

mapped or stroked characters.
 A charsize value of 0 can be used only with

stroked fonts.

 Fonts
There are currently five fonts available . But it is
easy to add other to the systems. These are

Value Constant File Comment
0 DEFAULT_FONT Built in Bit-mapped, 8x8
1 TIPLEX-FONT TRIP.CHR Stroked (Times Roman style)
2 SMALL_FONT LITT.char Stroked (for small lette4rs)
3 SANS_SERIF_FON SANS.CHR Stroked( sans_serif style)
T
4 GOTHIC_FONT GOTHIC.CH Stroked (gothic style)
R

Lecture on graphics

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