#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);
   glColor4f(0.0, 1.0, 0.0, 1.0);
   glDisable(GL_DITHER);
}

static void test(void)
{    
   GLfloat *buf;
   int i, j;
   int colored = 0;

   glClear(GL_COLOR_BUFFER_BIT);

   glScissor(4, 3, 25, 1);
   glEnable(GL_SCISSOR_TEST);

   //glPointSize(2.0);
   glEnable(GL_POINT_SMOOTH);
   glBegin(GL_POINTS);
   for (i = 0; i < WINDSIZEX; i++) {
      for (j = 0; j < WINDSIZEY; j++) {
	 glVertex2f (i + 0.5, j + 0.5);
      }
   }
   glEnd();

   buf = (GLfloat *)malloc(WINDSIZEX*WINDSIZEY*sizeof(GLfloat));

   glReadPixels(0, 0, WINDSIZEX, WINDSIZEY, GL_GREEN, GL_FLOAT, buf);
   for ( i = 0; i < WINDSIZEX * WINDSIZEY; i++)
      if (buf[i] == 1.0)
	 colored++;
   printf("colored point number is %d, should be 25\n", colored);
}

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; 
}