I tried going over FDeferredShadingSceneRenderer::Render as the documentation suggested but its a really complicated area to look at it and after a couple of hours on it I’m still failing to get the overall picture. What I’m still failing to understand is the way shaders are getting binded to each pass and how each pass gets the list of primitives its supposed to render. Regarding the shaders pipeline, I figured out the way that expressions are compiled into HLSL code and then compiled again into intermediate shader language, so basically I got this area covered by now. I’m also interested about the way all the different rendering passes work and how they interact, also the way the scene graph provides the renderer the list of primitive components that the render will be using for each of its passes. The areas I’m most interested in at the moment are the way the material system works and how the expression nodes turn into shaders and how these shaders are binded and uses in the pipeline.

I am mostly interested in the rendering part of the engine as I’m currently trying to build my own simple game engine for practice. It is no small task and I seriously doubt there is anybody that truly understands the entire code base so finding anything like “here is how all of UE4 works” won’t happen. Read the code and use debugging to try and get a grasp on what it is doing. I recommend focusing on areas you wish to use. To have documentation on all of it simply is a task that will never happen. The engine is also updated daily, sometimes in very big ways. There is also code inherited from past versions of the engine which could be much older.

The engine code is massive and written by literally hundreds of people over the last 5+ years. If you have a problem with a specific portion of it, you can post on the AnswerHUB and maybe get an answer from one of the developers responsible for that section of the engine. The documentation portion of the website does a pretty good job documenting the gameplay framework but the rest of the engine is largely undocumented.

Unreal engine 5 source code