GETPIXEL
i = GETPIXEL(x, y);
uint32_t p00 = GETPIXEL(offset_x, offset_y);
uint32_t p01 = GETPIXEL(offset_x, offset_y1);
uint32_t p10 = GETPIXEL(offset_x1, offset_y);
uint32_t p11 = GETPIXEL(offset_x1, offset_y1);