I a nutshell, RTX Global Illumination is the ray-traced effect if indirect lighting through global light-sources in a scene, while direct illumination is concerned with the direct effect of light-sources in the scene. Think about the ambient light outside a house that refracts through windows, reflects from walls and furniture, changes color when shining through leaves on trees, etc. That is GI. Then imagine a desk lamp on a table shining on a book. That is direct illumination.
I read a documentation page you provided. Am I understood correctly that (according the documentation):
Instead of using volumes I can enable Direct Illumination (DI) via setting the parameter r.RayTracing.SampledLighting to 1
I will check the video on demand as well.
I have 2 questions:
How to enable RTXGI in Unreal 5.1?
And a question about your branch with caustics. Why do you need a separate branch for it? :)
I am not the expert in RTXDI, but maybe @rcowgill can answer your first question on Volumes vs SampleLighting.
Regarding RTXGI, the latest UE version we officially support with a plugin is 4.72. If you still want to use it you need to familiarize yourself with the official RTXGI SDK and integrate that into your project.
Why the Caustics branch differs from NvRTX main is something I do not know.
I am “just” a community manager, meaning I do have a wide range of expertise, but when it comes to deeper questions, I need to refer to the experts. And as it so happens, the experts actually have a day job which is not directly connected to forums and they are pretty busy.
That is why it can take a while until one of those experts jumps in to give feedback.
And if you need my attention, feel free to tag me in the original post, not in some other persons post. It is kind of bad style :-)