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

#define WINDSIZEX 100
#define WINDSIZEY 100

int useUnpackBuffer = 1;

void
init (void)
{
    int i;
    GLfloat white[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat black[] = { 0.0, 0.0, 0.0, 1.0 };
    GLfloat red[] = { 1.0, 0.0, 0.0, 1.0 };
    GLfloat green[] = { 0.0, 1.0, 0.0, 1.0 };
    GLfloat blue[] = { 0.0, 0.0, 1.0, 1.0 };

    glClearColor (0.0, 0.0, 0.0, 1.0);
    glColor4fv (white);
    gluOrtho2D (0, WINDSIZEX, 0, WINDSIZEY);
    glDisable (GL_DITHER);
}


#define TEXSIZE 8
static void
test (void)
{
    int i, j;
    GLuint pb_unpack[1];
    GLubyte bitmap[TEXSIZE * TEXSIZE / 8];
    GLfloat buf[WINDSIZEX * WINDSIZEY * 3];
    GLubyte * pboUnpackMem = NULL;
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glColor3f (1.0, 1.0, 1.0);

    if (useUnpackBuffer) {
       glGenBuffersARB(1, pb_unpack);
       glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_EXT, pb_unpack[0]);
       glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_EXT, TEXSIZE * TEXSIZE, NULL,
                    GL_STREAM_DRAW);
       pboUnpackMem = (GLubyte *) glMapBufferARB(GL_PIXEL_UNPACK_BUFFER_EXT,
                                       GL_WRITE_ONLY);
    }
    else {
       pboUnpackMem = bitmap;
    }


    for (i = 0; i < TEXSIZE * TEXSIZE / 8; i++) {
       pboUnpackMem[i] = 0xAA;
    }


    glClear (GL_COLOR_BUFFER_BIT);
    glRasterPos2f (0.0, 0.0);

    glPixelStorei (GL_UNPACK_ALIGNMENT, 1);
    if (useUnpackBuffer) {
       glUnmapBufferARB(GL_PIXEL_UNPACK_BUFFER_EXT);
       glBitmap(TEXSIZE, TEXSIZE, 0, 0, 0, 0, NULL);
       glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_EXT, 0);
    }
    else
       glBitmap(TEXSIZE, TEXSIZE, 0, 0, 0, 0, pboUnpackMem);


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

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)
{
    if (argc > 1)
	useUnpackBuffer = 0;
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize (WINDSIZEX, WINDSIZEY);
    glutInitWindowPosition (100, 100);
    glutCreateWindow (argv[0]);
    init ();
    glutDisplayFunc (display);
    glutMainLoop ();
    return 0;
}