codigo base

#include <GL/gl.h>
#include <GL/glut.h>

void display(void)
{
/*  clear all pixels  */
    glClear (GL_COLOR_BUFFER_BIT);

/*  draw white polygon (rectangle) with corners at
 *  (0.25, 0.25, 0.0) and (0.75, 0.75, 0.0)  
 */
    glColor3f (1.0, 1.0, 1.0);
    glBegin(GL_LINES);
        glVertex3f (0.25, 0.25, 0.0);
        glVertex3f (0.75, 0.25, 0.0);
        glVertex3f (0.75, 0.75, 0.0);
        glVertex3f (0.25, 0.75, 0.0);
    glEnd();

/*  don't wait!  
 *  start processing buffered OpenGL routines 
 */
    glFlush ();
}

void init (void) 
{
/*  select clearing (background) color       */
    glClearColor (0.0, 0.0, 0.0, 0.0);

/*  initialize viewing values  */
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 4.0, 0.0, 4.0, -2.0, 4.0);
}

/* 
 *  Declare initial window size, position, and display mode
 *  (single buffer and RGBA).  Open window with "hello"
 *  in its title bar.  Call initialization routines.
 *  Register callback function to display graphics.
 *  Enter main loop and process events.
 */
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize (250, 250); 
    glutInitWindowPosition (100, 100);
    glutCreateWindow ("hello");
    init ();
    glutDisplayFunc(display); 
    glutMainLoop();
    return 0;   /* ISO C requires main to return int. */
}

nota  

void glOrtho(GLdouble left,
             GLdouble right,
             GLdouble bottom,
             GLdouble top,
             GLdouble near,
             GLdouble far)

vertices 2 dimensiones:  V0- 0,0 v1=2,0 v2= 2,2 v3=0,2 v4= 3.73,3 v5=3.73,3 v6= 1.73,3 v7= 1.73,1
vertices 3 dimensiones: v0=0,0,0  v1=2,0,0 v2=2,2,0 v3=0,2,0 v4=2,0,-2 v5= 2,2,-2 v6=0,2,-2 v7=0,0,-2