/*  simple.c  This program draws a red rectangle on a green background.*/
/* E. Angel, Interactive Computer Graphics */
#include <GL/glut.h>  /* glut.h includes gl.h and glu.h*/

void display(void)
{
  /* clear window */
  glClear(GL_COLOR_BUFFER_BIT); 

  /* draw unit square polygon */
  glBegin(GL_POLYGON);
    glVertex2f(-0.5, -0.5);
    glVertex2f(-0.5, 0.5);
    glVertex2f(0.5, 0.5);
    glVertex2f(0.5, -0.5);
  glEnd();

  /* flush GL buffers */
  glFlush(); 
}

void init()
{
  /* set clear color to black (0,0,0,0) default, or green (0,1,0,0)*/
  glClearColor (0.0, 1.0, 0.0, 0.0);
  /* set fill  color to white (1,1,1) default, or red (1,0,0)*/
  glColor3f(1.0, 0.0, 0.0);

  /* set up standard orthogonal view with clipping */
  /* box as cube of side 2 centered at origin */
  /* This is default view and these statement could be removed */
  glMatrixMode (GL_PROJECTION);
  glLoadIdentity ();
  glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
}

int main(int argc, char*argv[])
{
  /* Initialize mode and open a window in upper left corner of screen */
  /* Window title is name of program (arg[0]) */
  glutInit(&argc,argv);  /* optional */
  /* following three lines may be omitted, default */
  glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);  
  glutInitWindowSize(300,300);
  glutInitWindowPosition(0,0); 
  
  glutCreateWindow("simple"); 
  glutDisplayFunc(display);  /* !!! "display" called */
  init();                    /* !!! "init" called */
  glutMainLoop();
  return 0;
}