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COMPUTER GRAPHICS

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[email protected]

TA: Nouf Al-harbi

What’s Computer Graphics?..2

Computer

Image Description

Computer Graphics

How we look at an image!• Color: B/W or color (RGB)• Frame: length, width• Size: length, width, area,

height and volume if 3D• Type: Static or animated• Content: The scene:

Objects, characters• Background/ Foreground• lighting, shading• Textures• Viewing angle: camera

location

How The computer see an image!

The computer generally sees an image as a set of square points or PIXELS (Picture Elements)

Each Pixel having a defined RGB color

These pixels and their colors are processed to extract information about the image content

COMPUTER GRAPHICS LAB OBJECTIVETo give you a good practical experience in programming graphics using C++ and OpenGL

Introductiom to OpenGL

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LAB MARKS


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LAB MATERIALS.. NoufNaief.net

Introductiom to OpenGL 7

COMPUTER GRAPHICSLAB 1

Introduction to OpenGL

objectives• By the end of this lab you will be able to know :

• What’s OpenGl ..?• What does it do ? And what doesn’t it do..?• What’s GLUT and why do we use it ..? • Write the 1st OpenGL program


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What is OpenGL?• OpenGL stands of Open Graphical Library • It is a software interface to graphics hardware.• It consists of about 120 distinct commands

• to specify the objects and operations needed to produce interactive 3D applications

• It is developed by many companies and it is free to use• You can develop OpenGL-applications without Licensing

• OpenGL is a system-independent interface• it can work with any programming language and any operating system


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What I can do with OpenGL ..?

• This picture may give you an idea of the kinds of things you can do with the OpenGL graphics system

• This picture is the cover of the ‘Red Book’: OpenGl Programming user guide


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What OpenGL doesn’t do?


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With OpenGL you must

• OpenGL doesn’t

•Work through whatever windowing system controls the particular hardware you're using.•GLUT can be used.

•OpenGL is window system independent it doesn’t include commands for

•performing windowing tasks •obtaining user input

•Build up your desired model from a small set of geometric primitive - points, lines, and polygons.

•OpenGL doesn’t provide commands that allowing you to specify complicated shapes

• Automobiles• parts of the body• airplanes

THE SUPPORT LIBRARIESGLU and GLUT


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GLUT• The OpenGL Utility Toolkit (GLUT) is a Programming

interface• It implements a simple windowing application

programming interface (API) for OpenGL• The toolkit supports the following functionality :

• Create Display windows.• Interactive with input devices and detect user input.• An “idle” routine and timers.• Utility routines to generate various solid and wire frame objects.

Introduction to OpenGL

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GLU

•GLU: OpenGL Utility Library• provides functions for drawing more complex primitives than those of OpenGL• such as curves and surfaces


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OpenGL Basics• Function names:

• Begins with gl .• Each component word starts with capital letter.

• Examples:• glClear( )• glClearColor( )


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OpenGL Basics• Basic Constants:

• Starts with GL• Component words are written in Capital letters and separated by

underscore ( _ ).

• Examples:• GL_COLOR_BUFFER_BIT• GL_POINTS• GL_LINES


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OpenGL Basics• All the functions in GLUT starts with glut• All the functions in GLU starts with glu


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your first OpenGL Program• Preparing the graphics work environment • We will use VC++ • You need to include these files to your computer


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Where to put these files?

Microsoft Visual Studio/VC98/Lib

opengl32.libglu32.libglaux.libglut32.lib

Library files

Microsoft Visual Studio/VC98/Include/GL

Note: all header files are in folder GL

gl.hglu.h

glaux.hglut.h

Header files

Windows/system32

Opengl32.dllGlu32.dllGlut32.dll

DLL files

your first OpenGL ProgramGenerate a square on a solid background

• Open VC++ • New source file• Write the following code• Compile and build it

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#include <GL/glut.h> void display() { glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POLYGON); glVertex2f(-0.5, -0.5); glVertex2f(-0.5, 0.5); glVertex2f(0.5, 0.5); glVertex2f(0.5, -0.5); glEnd(); glFlush();} int main(int argc, char** argv){ glutInit(&argc,argv); glutCreateWindow("CS447 First OGL Program"); glutDisplayFunc(display); glutMainLoop();}

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your first OpenGL Program

• You have to link used libraries to your project • Select Project/Settings from the main menu.• A dialog box appears, select the Link tab.• Add the following files to the Object/library modules:

opengl32.lib

glut32.lib

glu32.lib


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your first OpenGL Program

• To write OpenGL program, we must include these files • glut. h• glu. h • gl. h

• #include <GL/glut.h> should automatically include the others


#include <GL/glut.h> 1

your first OpenGL Program • There are 2 functions in our program • Display function• Main function

• Each of them calls a number of OpenGL/glut functions


#include <GL/glut.h> void display() { glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POLYGON); glVertex2f(-0.5, -0.5); glVertex2f(-0.5, 0.5); glVertex2f(0.5, 0.5); glVertex2f(0.5, -0.5); glEnd(); glFlush();} int main(int argc, char** argv){ glutInit(&argc,argv); glutCreateWindow("CS447 First OGL Program"); glutDisplayFunc(display); glutMainLoop();}

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Main Function Commands

• Initializes GLUT •should be called before any OpenGL command

• takes the arguments from main()Introductiom to OpenGL 24

int main(int argc, char** argv){ glutInit(&argc,argv); glutCreateWindow("CS447 First OGL Program"); glutDisplayFunc(display); glutMainLoop();}

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Creates a window on the screen with the title Parameters:

• Title of the window would be created Returns an integer that can be used to refer to the window in multi-

window situations.



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The function display() is called each time there is

a display callback• Parameters:

• A function that contains what we want to draw in the screen



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In order to respond to theinput event, the application must provide a function – known as a callback function – tohandle the event; OpenGL automatically calls the application’s function, passing it the eventdata.


• Causes the program to enter an event-processing loop• Once called, this routine will never return.• It will call as necessary any callbacks that have been

registered. • This statement should be the last one in the main()

function



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Display Function Commands

• called by GLUT when the window is redrawn.• we should specify what we want to output to screen.


void display() { glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POLYGON); glVertex2f(-0.5, -0.5); glVertex2f(-0.5, 0.5); glVertex2f(0.5, 0.5); glVertex2f(0.5, -0.5); glEnd(); glFlush();}

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Display Function Commands • clears one or more of

OpenGL’s buffers.• When glClear() is called,

each pixel in the buffer is set to the current clear color, which is set to black by default.

• Parameters:

• GL_COLOR _BUFFER_BIT:• frame buffer, which holds the

pixels which will be copied to the window



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OpenGL doesn’t draw its graphics directly to the window. It actually draws into a data structure (an array of pixels) inside OpenGL called the frame-buffer. Periodically, OpenGL copies the pixels in the frame buffer into the window.


• Specifies the beginning of an object of type mode• Modes include:

• GL_POINTS• GL_LINES• GL_POLYGON , …etc.



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glVertex{234}{sifd}(X_coordinate, Y_coordinate,...)

• {234} Specifies the location of a vertex in two, three, or four dimensions with the types short (s), int (i), float (f), or double (d)



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(0,0)x (1,0)

(0- ,1)

-(1,0)

(0,1)


• Specifies the end of a list of vertices.


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•instructs OpenGL to make sure the screen is up to date.• it causes the contents of any internal OpenGL buffers are “flushed” to the screen


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REFERENCES:• Materials of this lab are prepared using:An Introduction to Graphics Programming with OpenGL

by : Toby Howard, School of Computer Science, University of Manchester

Lighthouse3d: http://www.lighthouse3d.com/opengl/glut/index.php?1

OpenGL Programming Guide 'The Red Book’Computer Graphics Lab -1st semester – 2010-2011 by :

Ins. Ruwaida Al-harbi & Ins. Nouf Al-harbiComputer Graphics Lectures – 1st semester 2009-2010

by Dr.Ahmed GhaliIntroductiom to OpenGL

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