#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);
    gluOrtho2D (0, WINDSIZEX, 0, WINDSIZEY);
    glDisable (GL_DITHER);
}

void Maketexture(GLsizei size, GLfloat *buf, long texnum)
{
    GLint level, i, j, k;

    for (i = 0; i < size; i++) {
        for (j = 0; j < size; j++) {
            k = (i * size + j) * 3;
            buf[k+0] = (texnum == 0) ? 0.0 : 1.0;
            buf[k+1] = (texnum == 0) ? 1.0 : 0.0;
            buf[k+2] = 1.0;
        }
    }

}

static void
test (void)
{
    int i, j;
    GLfloat buf[WINDSIZEX * WINDSIZEY * 3];
    GLuint numTextures, textureNames[2];
    GLfloat *textureBuf[2];

    glGetIntegerv(GL_MAX_TEXTURE_UNITS_ARB, &numTextures);
    if (numTextures <= 1)
	exit(0);

    glClearColor (0.0, 0.0, 0.0, 0.0);
    glColor3f (1.0, 1.0, 1.0);
    glClear (GL_COLOR_BUFFER_BIT);

    glGenTextures(2, textureNames);

    for (i=0; i<2; i++)
    {
        glActiveTextureARB(GL_TEXTURE0_ARB+i);
        glBindTexture(GL_TEXTURE_2D, textureNames[i]);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        textureBuf[i] = (GLfloat *)malloc(8*8*3*sizeof(GLfloat));
        Maketexture(8, textureBuf[i], i);
        glTexImage2D(GL_TEXTURE_2D, 0, 3, 8, 8, 0, GL_RGB,
                     GL_FLOAT, textureBuf[i]);
    }

    // enable two texture unit separately with GL_DECAL mode
    for (i=0; i<2; i++)
    {
        glActiveTextureARB(GL_TEXTURE0_ARB+i);
        glEnable(GL_TEXTURE_2D);
        glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
	glBegin(GL_POLYGON);
        glMultiTexCoord2fARB(GL_TEXTURE0_ARB+i, 0.0, 0.0);
        glVertex2i(0, 0);
        glMultiTexCoord2fARB(GL_TEXTURE0_ARB+i, 0.0, 1.0);
        glVertex2i(0, 8);
        glMultiTexCoord2fARB(GL_TEXTURE0_ARB+i, 1.0, 1.0);
        glVertex2i(8, 8);
        glMultiTexCoord2fARB(GL_TEXTURE0_ARB+i, 1.0, 0.0);
        glVertex2i(8, 0);
        glEnd();
//	glFlush();
	glReadPixels (0, 0, WINDSIZEX, WINDSIZEY, GL_RGB, GL_FLOAT, buf);
	glDisable(GL_TEXTURE_2D);
    }

    // enable two texture units together, with GL_MODULATE mode.
    for (i = 0; i < 2; i++) {
        glActiveTextureARB(GL_TEXTURE0_ARB+i);
        glEnable(GL_TEXTURE_2D);
        glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    }

    glBegin(GL_POLYGON);
    glMultiTexCoord2fARB(GL_TEXTURE0_ARB, 0.0, 0.0);
    glMultiTexCoord2fARB(GL_TEXTURE1_ARB, 0.0, 0.0);
    glVertex2i(0, 0);
    glMultiTexCoord2fARB(GL_TEXTURE0_ARB, 0.0, 1.0);
    glMultiTexCoord2fARB(GL_TEXTURE1_ARB, 0.0, 1.0);
    glVertex2i(0, 8);
    glMultiTexCoord2fARB(GL_TEXTURE0_ARB, 1.0, 1.0);
    glMultiTexCoord2fARB(GL_TEXTURE1_ARB, 1.0, 1.0);
    glVertex2i(8, 8);
    glMultiTexCoord2fARB(GL_TEXTURE0_ARB, 1.0, 0.0);
    glMultiTexCoord2fARB(GL_TEXTURE1_ARB, 1.0, 0.0);
    glVertex2i(8, 0);
    glEnd();



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