#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, 0.0);
}

static void test(void)
{    
   GLfloat buf[4];
   GLubyte fillPattern[128];
   int i;

   glClear(GL_COLOR_BUFFER_BIT);

   glColor3f(0.0, 1.0, 0.0);

   glEnable(GL_POLYGON_STIPPLE);
   for (i = 0; i < 128; i++) {
      fillPattern[i] = 0xFF;
   }
   glPolygonStipple(fillPattern);
   glBegin(GL_POLYGON);
      glVertex2f(1.0, 50.0);
      glVertex2f(70.0, 99.0);
      glVertex2f(80.0, 1.0);
   glEnd();

   glReadPixels(50, 50, 1, 1, GL_RGB, GL_FLOAT, buf);
   printf("draw pixel at (50, 50): %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; 
}