RenderPass &add_pass(const Tag &);
bool has_pass(const Tag &) const;
const RenderPass &get_pass(const Tag &) const;
+ const RenderPass *find_pass(const Tag &) const;
const PassMap &get_passes() const { return passes; }
bool replace_texture(const std::string &, const Texture &);
bool replace_material(const std::string &, const Material &);