#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#define WINDSIZEX 100
#define WINDSIZEY 100


void init(void)
{
   glClearColor(0.0, 0.0, 0.0, 1.0);
}

static void test(void)
{    
   GLfloat buf[4];

    //glDrawBuffer(GL_FRONT);
    //glReadBuffer(GL_FRONT);
   glClear(GL_COLOR_BUFFER_BIT);

   glReadPixels(5, 6, 1, 1, GL_RGBA, GL_FLOAT, buf);
   printf("draw pixel at (5, 6): %f %f %f\n", buf[0], buf[1], buf[2]);
}

void display(void)
{
    glViewport(0, 0, WINDSIZEX, WINDSIZEY);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
    gluOrtho2D(0, WINDSIZEX, 0, WINDSIZEY);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

    test();
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize(WINDSIZEX, WINDSIZEY);
   glutInitWindowPosition(100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutDisplayFunc(display);
   glutMainLoop();
   return 0; 
}