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

#define WINDSIZEX 100
#define WINDSIZEY 100


void init(void)
{
   glDisable(GL_DITHER);
   glClearColor(0.0, 0.0, 0.0, 1.0);
}

static void TextureTest()
{
   unsigned char t[] = {127, 63};
   GLuint texID;

   glGenTextures(1, &texID);
   glBindTexture(GL_TEXTURE_1D, texID);

   glEnable(GL_TEXTURE_1D);

   glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);

   glTexParameteri(GL_TEXTURE_1D, GL_DEPTH_TEXTURE_MODE, GL_ALPHA);//GL_LUMINANCE
   glTexImage1D(GL_TEXTURE_1D, 0, GL_DEPTH_COMPONENT, 2, 0,
	 GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, (void*)t);


   glBegin(GL_QUAD_STRIP);
   glTexCoord2f(0.25, 0.25);
   glVertex2i(25, 25);
   glTexCoord2f(0.25, 0.75);
   glVertex2i(25, 75);
   glTexCoord2f(0.75, 0.25);
   glVertex2i(75, 25);
   glTexCoord2f(0.75, 0.75);
   glVertex2i(75, 75);
   glEnd();

   glDisable(GL_TEXTURE_1D);
}

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

   glClear(GL_COLOR_BUFFER_BIT);
   glColor3f(1.0, 1.0, 1.0);

   TextureTest();

   glReadPixels(35, 50, 1, 1, GL_RGBA, GL_FLOAT, buf);
   printf("draw pixel at (35, 50): %f %f %f %f, the alpha component should be 0.5\n", buf[0], buf[1], buf[2], buf[3]);

   glReadPixels(65, 50, 1, 1, GL_RGBA, GL_FLOAT, buf);
   printf("draw pixel at (65, 50): %f %f %f %f, the alpha component should be 0.25\n", buf[0], buf[1], buf[2], buf[3]);
}

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); // | GLUT_DEPTH);
   glutInitWindowSize(WINDSIZEX, WINDSIZEY);
   glutInitWindowPosition(100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutDisplayFunc(display);
   glutMainLoop();
   return 0; 

}