file.c

        uint32_t max_coord = (uint32_t) -1;
        size_t orig_width  = (size_t) sc->width  * max_coord / (max_coord - r - l);
        size_t orig_height = (size_t) sc->height * max_coord / (max_coord - b - t);

        sc->spherical->left_bound   = ceil(orig_width  * l / max_coord);
        sc->spherical->top_bound    = ceil(orig_height * t / max_coord);
        sc->spherical->right_bound  = orig_width  - sc->width  - sc->spherical->left_bound;
        sc->spherical->bottom_bound = orig_height - sc->height - sc->spherical->top_bound;