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

#define WINDSIZEX 100
#define WINDSIZEY 100

void
init (void)
{
    int i;
    GLfloat white[] = { 1.0, 1.0, 1.0, 1.0 };

    glClearColor (0.0, 0.0, 0.0, 1.0);
    glColor4fv (white);
    glDisable (GL_DITHER);
}

#define TEXTURE_SIZE 4
#define TEXTURE_DEPTH 2

static void
test (void)
{
    int i, j;
    int texName;
    GLfloat image[TEXTURE_DEPTH * TEXTURE_SIZE * TEXTURE_SIZE * 4];
    GLfloat buf[WINDSIZEX * WINDSIZEY * 4];

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


    for (i=0; i<TEXTURE_DEPTH * TEXTURE_SIZE * TEXTURE_SIZE * 4; i++)
    {	
	if (i % 4 == 3)
		image[i] = 0.15;
	else
		image[i] = 0.5;
    }

    glBlendFunc(GL_ZERO, GL_SRC_ALPHA);

    glGenTextures (1, &texName);
    glBindTexture (GL_TEXTURE_3D, texName);

    glTexImage3D (GL_TEXTURE_3D, 0, GL_ALPHA, TEXTURE_SIZE, TEXTURE_SIZE, TEXTURE_DEPTH,
                  0, GL_ALPHA, GL_FLOAT, image);

    glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_CLAMP);
    glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri (GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    glClear (GL_COLOR_BUFFER_BIT);
    glEnable (GL_TEXTURE_3D);
    glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

    glEnable(GL_BLEND);
    glBegin (GL_POLYGON);
    glTexCoord3f (0.0, 0.0, 0.5);
    glVertex3f (0, 0, 0);
    glTexCoord3f (1.0, 0.0, 0.5);
    glVertex3f (4, 0, 0);
    glTexCoord3f (1.0, 1.0, 0.5);
    glVertex3f (4, 4, 0);
    glTexCoord3f (0.0, 1.0, 0.5);
    glVertex3f (0, 4, 0);
    glEnd ();
    glDisable(GL_BLEND);

    glReadPixels (0, 0, WINDSIZEX, WINDSIZEY, GL_RGBA, GL_FLOAT, buf);
    printf("buf[0, 0] = (%f, %f, %f, %f)\n", buf[0], buf[1], buf[2], buf[3]); 
    for (j = 0; j < WINDSIZEY; j++)
    {
        for (i = 0; i < WINDSIZEY; i++)
        {
            if (buf[(j * WINDSIZEX + i) * 4] != 0
                || buf[(j * WINDSIZEX + i) * 4 + 1] != 0
                || buf[(j * WINDSIZEX + i) * 4 + 2] != 0
                || buf[(j * WINDSIZEX + i) * 4 + 3] != 1.0)
            {
                printf ("(%d, %d) = [%f, %f, %f, %f]\n", i, j,
                        buf[(j * WINDSIZEX + i) * 4],
                        buf[(j * WINDSIZEX + i) * 4 + 1],
                        buf[(j * WINDSIZEX + i) * 4 + 2],
                        buf[(j * WINDSIZEX + i) * 4 + 3]);
            }
        }
    }
}

void
display (void)
{
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glOrtho (0, 100, 0, 100, 0, 2048);

    test ();
}

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