y = source->header.biHeight - (y + h);
    //assert(y >= 0 && y < source->header.biHeight);
    for (uint32_t i = y; i < y + h; ++i) {
        //assert(i < source->header.biHeight);
        for (uint32_t j = 3 * x; j < 3 * (x + w); ++j) {
            //assert(j < source->count);
            //assert(i - y >= 0 && j - 3 * x >= 0);
            //assert(i - y < result->header.biHeight);
            //assert(j - 3 * x < result->count);
            result->data[i - y][j - 3 * x] = source->data[i][j];
        }
    }