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

#define WINDSIZEX 100
#define WINDSIZEY 100

#define SIZEW 4
#define SIZEH 4

// Draw function used by many test casses
static void Draw()
{
   glBegin(GL_POLYGON);
   glVertex3f(25.0, 25.0, 0.0);
   glVertex3f(25.0, 75.0, 0.0);
   glVertex3f(75.0, 75.0, 0.0);
   glVertex3f(75.0, 25.0, 0.0);
   glEnd();

}


void init(void)
{
   glClearColor (1,1,1,1);
   glClearDepth(0.0);
   glDisable (GL_DITHER);
}

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

   glDepthFunc(GL_ALWAYS);
   glEnable(GL_DEPTH_TEST);
   glColor3f(0.0, 1.0, 0.0);
   glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
   glEnable(GL_POLYGON_OFFSET_FILL);
   glEnable(GL_POLYGON_OFFSET_LINE);
   glPolygonOffset(0.0, 3000.0);

   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   Draw();

   //Find depth values at different edges of the polygon
   glReadPixels(25, 50, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &buf[0]);
   glReadPixels(50, 25, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &buf[1]);
   glReadPixels(74, 75, 1, 1, GL_DEPTH_COMPONENT,GL_FLOAT,&buf[2]);
   glReadPixels(40, 75, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &buf[3]);


   printf("get depth values: %f %f %f %f\n", buf[0], buf[1], buf[2], buf[3]);
   printf("should above 0\n");
}

void display(void)
{
   glViewport(0, 0, WINDSIZEX, WINDSIZEY);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(0, WINDSIZEX, 0, WINDSIZEY, 0, 1);
   //gluOrtho2D(0, WINDSIZEX, 0, WINDSIZEY);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

   test();
}

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