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

#define WINDSIZEX 100
#define WINDSIZEY 100
#define TEXSIZE 16


void
init (void)
{
    int i;
    GLfloat white[] = { 1.0, 1.0, 1.0, 1.0 };
    //glViewport(0, 0, TEXSIZE, TEXSIZE);
    glClearColor (0.0, 0.0, 0.0, 1.0);
    glColor4fv (white);
    glDisable (GL_DITHER);
}


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 textures[1];
    GLubyte t[TEXSIZE * TEXSIZE * 4];
    int i, j;


    for (i=0; i<TEXSIZE*TEXSIZE*4; i++)
	t[i] = 0xFF;

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

    glGenTextures (1, textures);

    glBindTexture (GL_TEXTURE_2D, textures[0]);
    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
    glTexImage2D (GL_TEXTURE_2D, 0, 1, TEXSIZE, TEXSIZE, 0,
                  GL_RGBA, GL_UNSIGNED_BYTE, t);
    printf ("glTexImage2D: %s\n", gluErrorString (glGetError ()));

    // Draw to the window
    glEnable (GL_TEXTURE_2D);

    glColor4fv (white);
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glClear (GL_COLOR_BUFFER_BIT);

    glBegin (GL_POLYGON);
    glTexCoord2f (0.0, 0.0);
    glVertex2f (0, 0);
    glTexCoord2f (1.0, 0.0);
    glVertex2f (TEXSIZE, 0);
    glTexCoord2f (1.0, 1.0);
    glVertex2f (TEXSIZE, TEXSIZE);
    glTexCoord2f (0.0, 1.0);
    glVertex2f (0, TEXSIZE);
    glEnd ();
    GLfloat buf[WINDSIZEX * WINDSIZEY * 3];

    printf ("read out pixels:\n");
    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]);
            }
        }
    }
    glDeleteTextures(1, textures);
}

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 (100, 100);
    glutCreateWindow (argv[0]);
    init ();
    glutDisplayFunc (display);
    glutMainLoop ();
    return 0;

}