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

#define WINDSIZEX 100
#define WINDSIZEY 100

static void RenderPointPolygon (GLfloat xoff, GLfloat yoff, GLfloat texScale)
{
   glBegin (GL_POLYGON);
   glTexCoord2f (0.0, 0.0);
   glVertex2f (xoff + 0.0, yoff + 0.0);

   glTexCoord2f (texScale, 0.0);
   glVertex2f (xoff + 1.0, yoff + 0.0);

   glTexCoord2f (texScale, texScale);
   glVertex2f (xoff + 1.0, yoff + 1.0);

   glTexCoord2f (0.0, texScale);
   glVertex2f (xoff + 0.0, yoff + 1.0);
   glEnd ();
}

static void CreateTexture (GLint width, GLint height)
{
   GLfloat *buf, *buf0;
   GLint   i, j;

   buf = buf0 = malloc (3 * width * height * sizeof (GLfloat));

   for (i = 0; i < width; i++) 
   {
      for (j = 0; j < height; j++) 
      {
	 *buf++ = 1.0;
	 *buf++ = 1.0;
	 *buf++ = 0.0;
      }
    }
    glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, width, height, 0,
	 GL_RGB, GL_FLOAT, buf0);

   free (buf0);
}

void init(void)
{
   glDisable (GL_DITHER);

   glBindTexture (GL_TEXTURE_2D, 1);

   glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
   glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
   glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

   glEnable(GL_TEXTURE_2D);
}

static void test(void)
{  GLint level = 6;  
   GLfloat buf[18];
   GLint width = 1;
   GLint height = 1;
   GLint i;
   glClear (GL_COLOR_BUFFER_BIT);
   
   CreateTexture (width, height);
   glClear (GL_COLOR_BUFFER_BIT); 
   
   for (i = 1; i < level; i++)
   {
     
       RenderPointPolygon (i, 1.0, 1.0 / i);
         
   }

   
   
       
   glReadPixels(1, 1, level, 1, GL_RGB, GL_FLOAT, buf);
   for (i = 1; i <= level; i++)
   {  if ( buf[3*i-3] !=  1.0 || buf[3*i-2] != 1.0 || buf[3*i-1] != 0.0 )
        
      { printf("draw pixel  : %f %f %f\n", buf[3*i-3], buf[3*i-2], buf[3*i-1]);
        printf("draw pixel  should be: 1.0, 1.0, 0.0 \n");
        exit -1;
      }
   }
}

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; 
}