Detail Texture Example Program

Example 6-3 : Detail Texture Example

unsigned int tex[128][128];
unsigned int detailtex[256][256];

static void
make_textures(void) {
    int i, j;
    unsigned int *p;

    /* base texture is solid gray */
    p = &tex[0][0];
    for (i=0; i<128*128; i++) *p++ = 0x808080ff;

    /* detail texture is a yellow grid over a gray background     */
    /* this artificial detail texture is just a simple example    */
    /* you should derive a real detail texture from the original  */
    /* image as explained in the text.                            */
    p = &detailtex[0][0];
    for (i=0; i<256; i++) {
        for (j=0; j<256; j++) {
            if (i%8 == 0 || j%8 == 0) {
                *p++ = 0xffff00ff;
            } else {
                *p++ = 0x808080ff;
            }
        }
    }
}

static void
init(void) {
    make_textures();
    
    glEnable(GL_TEXTURE_2D);
    glMatrixMode(GL_PROJECTION);
    gluPerspective(90.0, 1.0, 0.3, 10.0 );
    glMatrixMode(GL_MODELVIEW);
    glTranslatef(0.,0.,-1.5);
    
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    
    /* NOTE: parameters are applied to base texture, not the detail */
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
                    GL_LINEAR_DETAIL_SGIS);
    glTexParameteri(GL_TEXTURE_2D, GL_DETAIL_TEXTURE_LEVEL_SGIS, -1);
    glTexImage2D(GL_TEXTURE_2D,
                 0, 4, 128, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex);
    glTexImage2D(GL_DETAIL_TEXTURE_2D_SGIS,
                 0, 4, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, 
                 detailtex);
}

static void
draw_scene(void) {
    glClear(GL_COLOR_BUFFER_BIT);
    glBegin(GL_TRIANGLE_STRIP);
        glTexCoord2f( 0, 0); glVertex3f(-1,-0.4, 1); 
        glTexCoord2f( 0, 1); glVertex3f(-1,-0.4,-1); 
        glTexCoord2f( 1, 0); glVertex3f( 1,-0.4, 1); 
        glTexCoord2f( 1, 1); glVertex3f( 1,-0.4,-1); 
    glEnd();
    glFlush();
}