#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 CUBE_MAP_SIZE 64
static GLfloat vertex[4][3] = {
    {-CUBE_MAP_SIZE / 2, +CUBE_MAP_SIZE / 2, -CUBE_MAP_SIZE / 2},
    {+CUBE_MAP_SIZE / 2, +CUBE_MAP_SIZE / 2, -CUBE_MAP_SIZE / 2},
    {+CUBE_MAP_SIZE / 2, -CUBE_MAP_SIZE / 2, -CUBE_MAP_SIZE / 2},
    {-CUBE_MAP_SIZE / 2, -CUBE_MAP_SIZE / 2, -CUBE_MAP_SIZE / 2},
};

#define I 2
static GLfloat positive_x_face[4][3] = {
    {+2, -2, +2}, {+2, -2, -2}, {+2, +2, -2}, {+2, +2, +2}
};

static void
test (void)
{
    int i, j, faceIndex;
    int texName;
    GLfloat CubeMap[6][CUBE_MAP_SIZE][CUBE_MAP_SIZE][3];
    GLfloat buf[WINDSIZEX * WINDSIZEY * 3];

    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f (1.0, 1.0, 1.0);
    glMatrixMode (GL_MODELVIEW);
    glLoadIdentity ();
    glGenTextures (1, &texName);
    glBindTexture (GL_TEXTURE_CUBE_MAP_ARB, texName);
    glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    glTexParameteri (GL_TEXTURE_CUBE_MAP_ARB, GL_TEXTURE_MIN_FILTER,
                     GL_NEAREST);
    glTexParameteri (GL_TEXTURE_CUBE_MAP_ARB, GL_TEXTURE_MAG_FILTER,
                     GL_NEAREST);

    for (faceIndex = 0; faceIndex < 6; faceIndex++)
    {
        for (i = 0; i < CUBE_MAP_SIZE; i++)
        {
            for (j = 0; j < CUBE_MAP_SIZE; j++)
            {
                CubeMap[faceIndex][i][j][0] = faceIndex==0? 1.0:0.0;
                CubeMap[faceIndex][i][j][1] = faceIndex==4? 1.0:0.0;
                CubeMap[faceIndex][i][j][2] = 0.0;
            }
        }
    }

    for (j = 0; j < 6; j++)
    {
        glTexImage2D (GL_TEXTURE_CUBE_MAP_POSITIVE_X_ARB + j,
                      0,
                      GL_RGB,
                      CUBE_MAP_SIZE,
                      CUBE_MAP_SIZE, 0, GL_RGB, GL_FLOAT, CubeMap[j]);
    }

    glDisable (GL_TEXTURE_GEN_S);
    glDisable (GL_TEXTURE_GEN_T);
    glDisable (GL_TEXTURE_GEN_R);
    glEnable (GL_TEXTURE_CUBE_MAP_ARB);
    glColor3f (1.0, 1.0, 1.0);

    glBindTexture (GL_TEXTURE_CUBE_MAP_ARB, texName);
    glBegin (GL_POLYGON);
    for (i = 0; i < 4; i++)
    {
        glTexCoord3f (positive_x_face[i][0], positive_x_face[i][1],
                      positive_x_face[i][2]);
        glVertex3f (vertex[i][0], vertex[i][1], vertex[i][2]);
    }
    glEnd ();
    glFlush ();

    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]);
            }
        }
    }
}

void
display (void)
{
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glOrtho (-50, 50, -50, 50, 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;
}