cg labmanual

7/31/2019 CG LabManual

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G. H. RAISONI INSTITUTE OF INFORMATION TECHNOLOGY, NAGPUR

MCA DEPARTMENT

LAB MANUAL

COMPUTER GRAPHICS

MCA II SEMESTER II

FACULTY

Mr. DILEEP SADHANKAR


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CONTENTS

1. Course Introduction

2. Fundamentals Of Computer Graphics

2.1 Objectives

2.2 Introduction

2.3 Display Technology

2.4 Pixel Concept

2.5 Resolution

2.6 Colour Models

2.7 Graphics Primitives

3. Programming graphics applications in Turbo C++

3.1 Objectives3.2 Introduction

3.3 Useful Graphic Functions.

3.3.1 initgraph

3.3.2 closegraph

3.3.3 setcolor

3.3.4 cleardevice

3.3.5 delay

3.3.6 moveto

3.3.7 lineto3.3.8 line

3.3.9 circle

3.3.10 getmaxx

3.3.11 getmaxy

3.3.12 putpixel

3.3.13 setlinestyle

3.3.14 outtextxy

3.4 Steps to use graphics (in Turbo C++ )

3.5 Programming in Graphics

4. Lab Assignments

5. Practical Programs List

6. References and further reading


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Course Introduction

The proverb A Picture is worth a thousand words tells us how a image/picture may be

useful to represent information. Computer Graphics provides one of the most natural means

for communicating & representing useful information. Graphics is used for education,

training, & entertainment applications development.

In the Lab sessions, we will have implementation of graphics primitives ,Line clipping

algorithm, Transformation, curve generation algorithm using C++ Language, Language

that you have learnt in Semesters I.


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2. Fundamentals of Computer Graphics

2.1 Objectives

The objective is to give students a good understanding of basic concepts

of computer graphics .

2.2 Introduction

Computer graphics cover various areas of knowledge, including the representation of graphic

elements (text, image or video), as well as their transformations (rotation, translation) by

means of algorithms.

2.3 Display Technology

The image is shown on a screen (also called a monitor), which is an output peripheral device

that allows a visual representation to be offered. The processor does not directly send

information to the monitor, but processes the information coming from its Random access

memory (RAM), then sends it to a graphics card that converts the information into electrical

impulses, which it then sends to the monitor.

Computer monitors are usually cathode tubes, i.e. a tube made out of glass in which an

electron gun emits electrons which are then directed by a magnetic field towards a screen on

which small phosphorescent elements are laid out, constituting points (pixels) that emit light

when the electrons hit them

2.4 Pixel Concept

The word pixel is an abbreviation ofPICture ELementThe pixel is thus the smallest

component of a digital image. An image consists of a set of (points) pixels

If system has VGA or better then screen has 640 pixels across and 480 pixels down.

640 X 480 = 307,200 pixels. The upper left corner is position (0, 0).The lower right corner is

position (639, 479) & the computer starts counting with zero.

(0,0) (639,0)

(0,479) (639,479)

The Graphics Screen Dimensions

The direction of the X-axis is from left to rightThe direction of the Y-axis is from top to bottom


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2.5 Resolution

A Two dimensional term that measures the number of scan-lines and the number of pixels on

each line (maximum number of points that can be displayed without overlap on a CRT)

2.6 Colour Models

Color models mathematically describe how colors may be represented. There are severalestablished color models used in computer graphics.

Color Model Decription

RGB

(Red,Green,Blue)Additive color model.

For computer displays.

Uses light to display color.

Colors result from transmitted

light.

Red+Green+Blue=White.

CMYK (Cyan-

Magenta-Yellow-

blacK)

Subtractive color model

For printed material

Uses ink to display color

Colors result from reflected light

Cyan+Magenta+Yellow=Black

LAB Lab is not device-dependent. In this three-

dimensional model, the L stands for the

lightness of the color, with 0 producing

black and 100 producing a diffuse white.The a is the redness vs. greenness, while

the b is the yellowness vs. blueness.

Color Models Description


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HSV(hue,

saturation, and

value)

HSV depicts three-dimensional color.

Consider HSV as a wheel of cheese, the

center axis goes from white at the top to

black at the bottom, with other neutral

colors in between. The angle from the axis

depicts the hue, the distance from the axis

depicts saturation, and the distance along

the axis depicts value.

HSL(hue,

saturation, and

lightness)

The HSL color model has distinct

advantages over the HSV model, in that

the saturation and lightness components

span the entire range of values. In the

bicone or diamond of the HSL structure,

all the visible colors can be seen. The hue

is comprised of the second and third

dimensions (corresponding to round slices

through the diamond).

NCS NCS colors have three values: darkness,

saturation, and hue. The hue is defined as

a percentage between two of the following

colors: red, yellow, green, and blue. The

NCS color system is expressed as the

percentage of darkness, the percentage of

saturation, and the percentages of two of

the opponent colors.

2.7 Graphics Primitives

Graphics Primitives are the basic elements that are used to represent graphics.

(1) Point : Specified by ordered pair (x,y) in plane.

(2) Line: Cannot measure how long it is.

(3) Line Segment: Length can be measured& has two end points.

(4) Vectors: Quantity that has Size/Magnitude & Direction.No Fixed Position in Space.

(5) Rectangle,Polygon,Triangle

(6) Circle,conic sections,Curved Surface


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3. Development of Graphics Applications

3.1. Objectives

The objective is to

Learn the hardware involved in building graphic applications.Learn algorithmic development of graphic primitives like: line, circle, ellipse,

polygon etc.Learn the representation and transformation of graphical primitives.

3.2. Introduction

Using C++ language it is possible to design the graphics based programs. The graphics

functions are defined in graphics.h file

3.3. Useful Graphic Functions.

3.3.1. initgraph:

Syntax :

void initgraph(int *graphdriver, int *graphmode, char *pathtodriver);

Description:

initgraph initializes the graphics system by loading a graphics driver from disk (or

validating a registered driver), and putting the system into graphics mode. User cantell initgraph to use a particular graphics driver and mode, or to autodetect the

attached video adapter at run time and pick the corresponding driver.

Normally, initgraph loads a graphics driver by allocating memory for the driverthen loading the appropriate .BGI file from disk.

pathtodriver specifies the directory path where initgraph looks for graphics drivers.

initgraph first looks in the path specified in pathtodriver, then (if they are not there)

in the current directory. Accordingly, if pathtodriver is null, the driver files (*.BGI)

must be in the current directory.

*graphdriver is an integer that specifies the graphics driver to be used.

*graphmode is an integer that specifies the initial graphics mode (unless

*graphdriver equals DETECT; in which case, *graphmode is set by initgraph to the

highest resolution available for the detected driver).

After a call to initgraph, *graphdriver is set to the current graphics driver, and

*graphmode is set to the current graphics mode.


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Return Value

initgraph always sets the internal error code; on success, it sets the code to 0. If an

error occurred, *graphdriver is set to -2, -3, -4, or -5, and graphresult returns the

same value as listed below:

Constant Name

grNotDetected

grFileNotFound

grInvalidDriver

grNoLoadMem

Number

-2

-3

-4

-5

Meaning

Cannot detect a graphics card

Cannot find driver file

Invalid driver

Insufficient memory to load driver

3.3.2. closegraph:

Syntax :

#include

void closegraph();

Description :

closegraph deallocates all memory allocated by the graphics system, then restores

the screen to the mode it was in before you called initgraph. (The graphics system

deallocates memory, such as the drivers, fonts, and an internal buffer, through a call

to _graphfreemem.)

Return Value

None.

3.3.3. Setcolor:

Syntax :

setcolor(number);

Where (number) is a numeric constant from 0 through 15, or the symbolic

constant that represents the color. The number of colors depend on the graphics

mode user select using Turbo C++.The default settings allow for 16 color

choices.


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Description:

Sets the color of current drawing color. The drawing color is the value that pixels

are set to when program draws the lines etc.

The color numbers and names:

Color number

0

1

2

3

4

5

6

7

Name

Black

Blue

Green

Cyan

Red

Magenta

Brown

LightGray

Color number

8

9

10

11

12

13

14

15

Name

Darkgray

Lightblue

Lightgreen

Lightcyan

Lightred

Lightmagenta

Yellow

White

3.3.4. Cleardevice:

Syntax:

#include

void cleardevice(void);

Description

Cleardevice erases (that is, fills with the current background color) the entire

graphics screen and moves the CP (current position) to home (0,0).

Return Value

None.

3.3.5. Delay:

Syntax

#include "graphics.h"

void delay(int millisec);

Description


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The delay function is also available in conio.h. The function pauses the computation

for the the specified number of milliseconds.Return Value :

None.

3.3.6. Moveto():

Syntax: void moveto(int X,int Y)

Description : Use to move the pointer to a location on the graph without drawing

anything

3.3.7. Lineto() :

Syntax

#include

void lineto(int x, int y);

Description

lineto draws a line from the CP (current position) to (x,y), then moves the CP

to (x,y).

Return Value :

None.

3.3.8. line:

Syntax

#include

void line(int x1, int y1, int x2, int y2);

Description

line draws a line in the current color, using the current line style and

thickness between the two points specified, (x1,y1) and (x2,y2), withoutupdating the current position (CP).

Return Value :

None.

3.3.9. circle :

Syntax :

#include

void circle(int x, int y, int radius);


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Description :circle draws a circle in the current drawing color with its center at (x,y) and the

radius given by radius.

The linestyle parameter does not affect arcs, circles, ellipses, or pie slices. Only thethickness parameter is used.

Similarly for

arc ( x, y, startangle, endangle, radius);

ellipse ( x, y, startangle , endangle, x_radius, y_radius);

3.3.10. getmaxx :

Syntax :#include

int getmaxx(void);

Description :

getmaxx returns the maximum (screen-relative) x value for the current

graphics driver and mode.

For example, on a CGA in 320*200 mode, getmaxx returns 319. getmaxx isinvaluable for centering, determining the boundaries of a region onscreen,

and so on.

Return Value :getmaxx returns the maximum x screen coordinate

3.3.11. getmaxy :

Syntax :

#include

int getmaxy(void);

Description :

getmaxy returns the maximum (screen-relative) y value for the current

graphics driver and mode.

For example, on a CGA in 320*200 mode, getmaxy returns 199. getmaxy is

invaluable for centering, determining the boundaries of a region onscreen,

and so on.

Return Value :getmaxy returns the maximum y screen coordinate


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3.3.12. Putpixel:

Syntax :

#include

void putpixel(int x, int y, int color);

Description

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

Return Value :

None.

Note: The color argument can be in the range of n ordinary BGI color (from 0 to 15)

or an RGB color

For example: putpixel (100, 100, WHITE);

3.3.13. Setlinestyle (style, pattern, thickness);

Syntax :

#include

void setlinestyle(int linestyle, unsigned upattern, int thickness);

Description :

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

and so on.

The linesettingstype structure is defined in graphics.h as follows:

struct linesettingstype {

int linestyle;

unsigned upattern;

int thickness;


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};

linestyle specifies in which of several styles subsequent lines will be drawn

(such as solid, dotted, centered, dashed). The enumeration line_styles, which

is defined in graphics.h, gives names to these operators:

Value DescriptionName

SOLID_LINE 0 Solid line

DOTTED_LINE 1 Dotted line

CENTER_LINE 2 Centered line

DASHED_LINE 3 Dashed line

USERBIT_LINE 4 User-defined line style

thickness specifies whether the width of subsequent lines drawn will be normal or thick.

Name Value Description

NORM_WIDTH 1 1 pixel wideTHICK_WIDTH 3 3 pixels wide

upattern is a 16-bit pattern that applies only if linestyle is USERBIT_LINE (4). In that case,

whenever a bit in the pattern word is 1, the corresponding pixel in the line is drawn in the

current drawing color. For example, a solid line corresponds to a upattern of 0xFFFF (all pixels

drawn), and a dashed line can correspond to a upattern of 0x3333 or 0x0F0F. If the linestyle

parameter to setlinestyle is not USERBIT_LINE (in other words, if it is not equal to 4), you

must still provide the upattern parameter, but it will be ignored.

Note: The linestyle parameter does not affect arcs, circles, ellipses, or pie slices. Only the

thickness parameter is used.

Return Value :

If invalid input is passed to setlinestyle, graphresult returns -11, and the current line style

remains unchanged

3.3.14. outtextxy:

Syntax

#include

void outtextxy(int x, int y, char *textstring);

Description

outtextxy displays a text string in the viewport at the given position (x, y),

using the current justification settings and the current font, direction, and

size.

outtextxy is for use in graphics mode; it will not work in text mode.

Return ValueNone.


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3.4. Steps to use graphics (in Turbo C++ )

There are five steps that you need to follow to use graphics in Turbo C++

1. Tell the compiler that graphics commands will be used.

Include the preprocessor directive:

#include

2. Let C++ find out what kind of graphics card computer uses.

Declare two variables of type Integer

int graphdriver = DETECT, graphmode;

3. Initialize the Graphics System

4. Tell the system where to find Graphics routines (BGI files)

Use initgraph function to initialize the system & for graphics routines(set path if u know or

otherwise leave blank)

initgraph(&graphdriver, &graphmode, );

5. Close the graphics screen after you have finished drawing your graphics.

closegraph( );

3.5. Programming in Graphics

Sample Program to draw line using built-in functions

Step 1: Write the code in Turbo C++ editor & save the code with .cpp extension.

#include

#include

#includevoid main()

{

int graphicdriver=DETECT, graphicmode;initgraph(&graphicdriver,&graphicmode,);

line(100,100,200,300);

getch();

closegraph();

}

Step 2: Compile the codeStep 3 : Run the code


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Lab Assignments

Write a program using graphics built-in function

1. To find the current position of the cursor(getx,gety) , maximum value of X co-

ordinate & Y co-ordinate (getmaxx,getmaxy), center pixel position on screen.

2. To display graphics primitives Point ,Line , Rectangle, Circle, Ellipse.

Hint : use putpixel,line,rectangle,circle,ellipse function.

3. To understand how move, moverel, line, linerrel function works.

4. To display text at specified position on screen.

5. To draw concentric circles.

6. Draw Rotating wheel(Movement)


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Practical Programs List

1. Aim: Program to draw line using DDA line Algorithm.

DescriptionWrite an algorithm, draw a flowchart and develop a graphics program in

C++ to implement DDA line generation algorithm. Accept Co-ordinates of endpoints of

line as input & display line.

2. Aim: Program to draw line using BRESENHAM LINE Algorithm


C++ to implement BRESENHAM algorithm. Accept Co-ordinates of endpoints of line asinput & display line.

3. Aim: Program to draw thick line using BRESENHAM line algorithm.


C++ to implement BRESENHAM algorithm. Accept Co-ordinates of endpoints of line &

thickness(width) of line as input & display line.

4. Aim: Program to draw dotted line using BRESENHAM Line algorithm


C++ to implement BRESENHAM algorithm. Accept Co-ordinates of endpoints of line &

gap between the no. of pixels as input & display line.

5. Aim: Program to transform a polygon using Scaling


C++ , Accept Co-ordinates of vertices of polygon & scale factor as input & display Scaled

polygon.

6. Aim: Program totransform a polygon using rotation. (by using pivot-point)


C++ , Accept Co-ordinates of vertices of polygon & rotation angle as input & display the

result. (Rotation about an arbitrary Point).


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7. Aim: Program to translate a polygon using translation.in which values of polygon edges and

translation points will be given by user.


C++ , Accept Co-ordinates of vertices of polygon & translation factor as input & display

the result.

8. Aim: Program which shear a polygon relative to different reference lines(i.e. Y Shear & X-

Shear)


C++ . Accept Co-ordinates of vertices of polygon ,direction of shear ( X or Y) & shear

factor as input & display the result.

9. Aim: Program for Line clipping algorithm.


C++ . Accept the window co-ordinates ,draw a line, apply the cohen-sutherland algorithm

to clip a line against the window boundary & display clipped line.

10. Aim: Program to draw Curve using ARCDDA algorithm.


C++ to implement ARCDDA algorithm to draw curve. Accept co-ordinates of center of

curvature, arc angle & starting point of arc.

11. Aim: Program to draw Circle using ARCDDA algorithm.


C++ to implement ARCDDA algorithm to draw circle. Accept co-ordinates of center of

circle.


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12. References and further reading

Computer Graphics by Steven Harrington [TMH]

Computer Graphics by Hearn Baker [PHI]

Interactive Computer Graphics by Newman and Sproull

Computer Graphics by Rogers [TMH]

http://www.cs.colorado.edu/~main/bgi/doc/

http://www.mycplus.com/featured-articles/c-language-graphics-library-reference-part-1/

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