Open source reimplementation of GTA IV game engine in Unity
On main scene you will find the 'Loader' object, you can set your game directory there. Press play to start loading the map. Expect slow loading, even with multithread.
World objects are loaded by the WorldComposerMachine class, initially it loads WPL instances, then IDE objects. Texture conversion from BGR to RGB currently happens on shader, check for: gta_default.shadergraph