In the transition of Minecraft version 1.14 to 1.15, Mojang introduced some sweeping changes to the way rendering is performed; while the internal code still relies on GL1-era immediate-mode, block and entity renderer classes now provide their vertices to a specific RenderLayer* which are later rendered in ordered batches.
These changes broke a majority of Minecraft mods; in the process of porting a mod to 1.15, I had to frequently rely on a tool called “apitrace”, and I thought a quick how-to might come in handy for others struggling with similar problems. Apitrace allows capturing every OpenGL call an application makes, and later replaying these calls and inspecting the entire GL state machine at each rendering step.
For this tutorial, I am using the MultiMC launcher.