YTILE_HEIGHT
#define YTILE_SIZE (YTILE_WIDTH * YTILE_HEIGHT * 4)
offset = ((y / YTILE_HEIGHT) * width_in_blocks + (x / YTILE_WIDTH)) * YTILE_SIZE;
y = y % YTILE_HEIGHT;
offset = ((y / YTILE_HEIGHT) * width_in_blocks + (x / YTILE_WIDTH)) * YTILE_SIZE;
y = y % YTILE_HEIGHT;