UT DALLAS Erik Jonsson School of Engineering & Computer Science

FEARLESS engineering

OpenGL Programming

CS 4392 Computer Animation

Spring 2010

FEARLESS engineering

What is OpenGL?

• A low level graphics API for 2D and 3D

interactive graphics. OS independent.

• Descendent of GL (from SGI)

FEARLESS engineering

OpenGL

• Contains a library of over 200 functions

• Portable– Implementations available for nearly all hardware and

operating systems

– Input or windowing are not included in OpenGL• Options for Windows: GLUT, GLUI, FLTK, or MFC

• GLUT = OpenGL Utility Toolkit

• Implementations of GLUT exist for most computing environment

FEARLESS engineering

What OpenGL isn’t:

• A windowing program or input driver, since those couldn’t be OS independent.

GL: core graphics capability

GLU: utilities on top of GL

GLUT: input and windowing functions

FEARLESS engineering

Reading materials

• Red bible

• Blue bible

• Super bible

• http://www.opengl.org/sdk/docs/man/

• http://nehe.gamedev.net/

• http://www.xmission.com/~nate/tutors.html

• ……..

• ……….

• ………….

FEARLESS engineering

Computer Graphics Pipeline

Geometric Model Rendered Image

OpenGL

Rendering

Algorithm

FEARLESS engineering

The Visualization Problem

FEARLESS engineering

How does OpenGL work?

• From the programmer’s point of view:

– Specify geometric objects

– Describe object properties

– Define how they should be viewed

– Move camera or objects around for navigation

FEARLESS engineering

How does OpenGL work?

• OpenGL pipeline:

Model Transformation Projection Rasterization Display

FEARLESS engineering

Basic OpenGL Syntax

• Prefix: gl

glBegin, glEnd, glClear, glPolygonMode, …

• Constant symbols: GL_

GL_RGB, GL_POLYGON, GL_LINES, …

• Data types: GL

GLbyte, GLshort, GLint, GLfloat, GLdouble, …

FEARLESS engineering Copyright @

Xiaohu Guo

OpenGL Commands: a Quick Look

Just function calls:

glColor3f (1.0, 1.0, 1.0);

Same command, different arguments:

glColor3ub(255,255,255); -- same result

GL prefix

Command name

Type suffix (if variable),

can also end with “v”

Number of arguments (if variable)

FEARLESS engineering

OpenGL Data Types

b 8 GLbyte signed char

s 16 GLshort short

i 32 GLint, GLsizei int / long

f 32 GLfloat, GLclampf float

d 64 GLdouble, GLclampd double

ub 8 GLubyte, Glboolean unsigned char

us 16 GLushort unsigned short

ui 32 GLuint, GLenum,

GLbitfield

unsigned int

FEARLESS engineering

OpenGL as a State Machine

• OpenGL has a state

– And associated state variables (line width, color, … etc.)

• eg. GL_FLAT & GL_SMOOTH are two states of GL_SHADE_MODEL

– Some states are binary states that are either GL_FALSE or GL_TRUE

– Each state variable has a default value.

• Changing states

– For binary state variables, use glEnable/glDisable (eg. GL_LIGHTING)

– Mode state variables require specific commands (eg. glShadeModel)

– Value state variables require specific commands too. (eg. glColor3f)

• Remains in effect until changed!

FEARLESS engineering

What is to be covered?

• Drawing

• Viewing

• ..

• ….

• …..

• …….

FEARLESS engineering Copyright @

Xiaohu Guo

Drawing

• Geometric object is described by the type of the primitive to be drawn and a set of vertices.

– GL_POINTS

– GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP

– GL_TRIANGLES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN

– GL_QUADS, GL_QUAD_STRIP

– GL_POLYGON

FEARLESS engineering

Drawing

• Put GL into draw-polygon state:glBegin (GL_POLYGON);

• Send it the points making up the polygon:glVertex2f (x0, y0);

glVertex2f (x1, y1);

glVertex2f (x2, y2); …

• Tell it we’re finishedglEnd();

FEARLESS engineering

Viewing

• Set the object

• Set the camera

• Set the projection

FEARLESS engineering

Transformation

• glTranslate

• glRotate

• glScale

• glPushMatrix(); glPopMatrix();

FEARLESS engineering

Projection

• glPerspective(……)

• glOrtho(…..)

FEARLESS engineering

A real OpenGL program

• int main(int argc, char** argv)

• {

• glutInit(&argc, argv);

• glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);

• glutInitWindowSize (500, 500);

• glutInitWindowPosition (100, 100);

• glutCreateWindow (argv[0]);

• init ();

• glutDisplayFunc(display);

• glutReshapeFunc(reshape);

• glutMainLoop();

• return 0;

• }

FEARLESS engineering

glutDisplayFunc(display)

• void display(void)

• {

• glClear (GL_COLOR_BUFFER_BIT);

• glColor3f (1.0, 1.0, 1.0);

• glLoadIdentity (); /* clear the matrix */

• /* viewing transformation */

• gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

• glScalef (1.0, 2.0, 1.0); /* modeling transformation */

• glutWireCube (1.0);

• glFlush ();

• }

FEARLESS engineering

glutReshapeFunc(reshape)

• void reshape (int w, int h)

• {

glViewport (0, 0, (GLsizei) w, (GLsizei) h);

glMatrixMode (GL_PROJECTION);

glLoadIdentity ();

glFrustum (-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);

glMatrixMode (GL_MODELVIEW);

}