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

#define WINDSIZEX 100
#define WINDSIZEY 100
#define TEXSIZE 8


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);

    // Check if GL_EXT_framebuffer_object is supported
    if (!strstr (glGetString (GL_EXTENSIONS), "GL_ARB_pixel_buffer_object"))
    {
        printf ("GL_ARB_pixel_buffer_object is not supported\n");
	exit(0);
    }
    else
    {
        printf ("GL_ARB_pixel_buffer_object is supported\n");
    }
}


static void
test (void)
{
    GLfloat red[] = { 1.0, 0.0, 0.0, 1.0 };
    GLfloat white[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat green[] = { 0.0, 1.0, 0.0, 1.0 };
    GLuint pbs[1];
    GLuint textures[1];
    int i, j;


    glClearColor (0.0, 0.0, 0.0, 1.0);
    glClear (GL_COLOR_BUFFER_BIT);

    GLubyte buffer[WINDSIZEX * WINDSIZEY * 4];
    for (i = 0; i < WINDSIZEX * WINDSIZEY * 4; i++)
        buffer[i] = i % 16;
    glDrawPixels(WINDSIZEX, WINDSIZEY, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glGenBuffers(1, pbs);
    glBindBuffer(GL_PIXEL_PACK_BUFFER_EXT, pbs[0]);
    glBufferData(GL_PIXEL_PACK_BUFFER_EXT, TEXSIZE*TEXSIZE*4, NULL, GL_STREAM_DRAW);
    glReadPixels(0, 0, TEXSIZE, TEXSIZE, GL_BGRA, GL_UNSIGNED_BYTE, NULL);

    GLubyte *b = (GLubyte *) glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY);

    for (j = 0; j < TEXSIZE; j++)
    {
        for (i = 0; i < TEXSIZE; i++)
        {
                printf ("(%d, %d) = [%d, %d, %d, %d]\n", i, j,
                        b[(j * TEXSIZE + i) * 4],
                        b[(j * TEXSIZE + i) * 4 + 1],
                        b[(j * TEXSIZE + i) * 4 + 2],
                        b[(j * TEXSIZE + i) * 4 + 3]);
        }
    }
}

void
display (void)
{
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    gluOrtho2D (0, WINDSIZEX, 0, WINDSIZEX);
    test ();
}

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

}