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