Implemented depth-based alpha blending rendering.

src/utility/config_utility.hpp

@@ -31,7 +31,7 @@ inline auto LOAD_BOOL_ITEM2(const nlohmann::json &config,
 inline auto LOAD_FLOAT_ITEM2(const nlohmann::json &config,
                              const std::string &item_name) {
     assert(config.contains(item_name));
-    assert(config[item_name].is_boolean());
+    assert(config[item_name].is_number());
     return config[item_name].get<double>();
 }