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

#define WINDSIZEX 100
#define WINDSIZEY 100

#define W 40
#define H 40

void init(void)
{
   glClearColor(0.0, 0.0, 0.0, 0.0);
   glColor3f(0.5, 0.0, 0.0);
   glDisable(GL_DITHER);

}

static void test(void)
{    
   GLfloat buf[WINDSIZEX*WINDSIZEY*3];
   int size;
   int i;
   GLubyte dataBuf[W*H*3];

   glRasterPos2f(-1.0, -1.0);

   //    polyWidth = W * 2.0 / WINDSIZEX;
   glPixelStorei(GL_UNPACK_ROW_LENGTH, W);

   size = W * H;

   for (i = 0; i < size; i++) {
      dataBuf[i] = 255;
      dataBuf[i+1] = 255;
      dataBuf[i+2] = 255;
   }
   glClear(GL_COLOR_BUFFER_BIT);
   glDrawPixels(W, H, GL_RGB, GL_UNSIGNED_BYTE, dataBuf);

   glReadPixels(0, 0, WINDSIZEX, WINDSIZEY, GL_RGB, GL_FLOAT, buf);
   printf("draw pixel at (0, 0): %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; 
}