#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>

/*  OpenGL with prototypes for glext */
#define GL_GLEXT_PROTOTYPES
#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

/*  Globals */
double dim=2; /* dimension of orthogonal box */
char *windowName = "Hello OpenGL";

/*
 *  Display the scene
 */
void display()
{
  glClear(GL_COLOR_BUFFER_BIT);
  glLoadIdentity();
  
  /* draw something */
  glBegin(GL_POLYGON);
  glColor3f(1.0,0.0,0.0);
  glVertex2f(0.0,0.5);
  glColor3f(0.0,1.0,0.0);
  glVertex2f(0.5,-0.5);
  glColor3f(0.0,0.0,1.0);
  glVertex2f(-0.5,-0.5);
  glEnd();

  glFlush();
  glutSwapBuffers();
}

/*
 *  GLUT calls this routine when the window is resized
 */
void reshape(int width,int height)
{
  double w2h = (height>0) ? (double)width/height:1;
  glViewport(0,0,width,height);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-dim*w2h,+dim*w2h,-dim,+dim,-dim,+dim);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

/*
 *  Start up GLUT and tell it what to do
 */
int main(int argc,char* argv[])
{
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
  glutInitWindowSize(500,500);
  glutCreateWindow(windowName);
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutMainLoop();
  return 0;
}