cairo_surface_t *tbg = nullptr;

    if (auto bg = const_cast<FilterSlot *>(this)->getcairo(NR_FILTER_BACKGROUNDIMAGE)) {

    auto bg_iter = _slots.find(NR_FILTER_BACKGROUNDIMAGE);

    if (bg_iter != _slots.end()) {

        auto bg = bg_iter->second;

        tbg = cairo_surface_create_similar(

            bg, cairo_surface_get_content(bg),

            _slot_w, _slot_h);