5.2 Caustics branch?

Can anyone tell me if the 5.2 Caustics branch is ready yet?
Couldn’t locate it.

Sorry, but no, it is not ready.

And I don’t know yet if or when it will be updated.

As a side note @bach44, I appreciate all the questions you are asking regarding the Caustics branch and the sample projects etc. I mentioned them to some people involved i the project beside Richard, but every one is pretty busy at the moment. I will remind them and hopefully they will look at your questions soon and give some feedback.


Thanks Markus.
Yes a bit caustics obsessed lately :)
Excited to see what I can create.

Hi @bach44 I’m one of developers responsible for caustics branch, we added many improvements in NvRTX Caustics 5.2.1, it’s gonna be released very soon, stay tuned !


Hi @bach44 NvRTX Caustics branch is out: https://github.com/NvRTX/UnrealEngine/tree/NvRTX_Caustics-5.2

  • Many errors were encountered during the build process

With me it worked out-of-the-box without issues

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Copy and paste BP_RTX to your project, it contains RT graphics salability preset , and then make some turnings based on your own project. Cheers!

@jackwang1 @MarkusHoHo

Working with the Caustics branch (5.2), I found an issues I would like to report… Can you give me some guidance on how (and if) / where to report issues?

The problem I’m having is connected to memory usage and resolution changes: Every time I change resolution some memory is ‘lost’. Since in my application (using pixelstreaming), the resolution changes regularly at each login, the game eventually just runs out of memory and crashes.

But again, if there’s a formal way to report a bug report I’ll be happy to make a full report there.


Hi @VTY , dynamic resolution and pixel streaming is the uncharted territory, we normally will support the real game request first, and then support none game feature :)

Hi @jackwang1 ,

Yes, you have to prioritize, I understand. But just to be clear: from what I can see the issue is a memory leak connected to choosing a resolution (pixel streaming itself has no issues).

Since you have to choose a resolution at least once also with gaming applications (and changing is also common, although perhaps not frequently) there may be some common gains in looking at this, also for gaming.

Anyhow, thanks for your support :)

Can you post a snapshot with stat d3d12 memory , stat rhi , and stat d3d12raytracing to indicate which pass is the culprit to cause the memory leak? If you are using crazy dxr rendering quality under a small GPU with less VRAM, it could be problematic.



Yes, of course. Here are some screenshots:

  1. Scene opening
  2. Scene after changing once between full-screen and windowed
  3. After changing a few times more
    Crash: the crash message

It’s a small scene with hardly any textures, not too many meshes, and a lot of caustics… :)

Let me know if you need any more info!


Thank you, I’ll try to repro the issue by using my kitchen glass cup scene. Any update I’ll let you know.

Hi @VTY ,

I tried to repro your memory leak issue on the similar demo scenario (I used the povray glass scene on my side), after multiple toggles from desktop and full screen operation (I just press alt+enter key many times), it seems VRAM is indeed released after a few seconds, you can check my captured video here: DeskTop_FullScreen_Toggle.mp4 - Google Drive

  1. If you sill encounter with the memory leak issue, try the same steps by using the vanilla UE 5.2.1 engine.

  2. In order to narrow down the root cause to further investigate this issue, disable dlss2 and dlss3 to check if the issue is still reproducible,


Hi @jackwang1 ,

Thank you for your support.

It took me a while, but given your input I managed to track down the original cause: I migrated the ‘BP_RT_Quality_Parameters’ blueprint from the UE5.1 project and failed to notice that there are some additional parameters set with it. Switching to the UE5.2 version solved the issue.

I do wonder still, though, which parameter was the root cause (because you would think that it justifies an amendment in ‘default settings’. With so many new parameters it would take me too long to do full A/B testing on each of them. Do you have any ideas?

In any case, the issue is solved so I’m happy :)


Basically, you need to use the corresponding preset version according to respective engine version, 5.2.1 should use the content from git read me page, the rendering pipeline is always evolving from version to version.

Very happy to hear the problem is resolved.


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i get many graphics errors using this branch what is the best driver version for this? latest drivers crash older drivers are a little better but still crashes a lot. lumen hardware ray tracing mode seems broken. using lumen and ray tracing modes in project settings causes a crash. colliding with translucent geometry while using mesh caustics reflection mode 1 or 2 causes crashes. switching to lumen or ray tracing causes crashes at runtime without project setting saying all shaders must be setup before. 5.2 nvrtx works fine. caustics branch very buggy

also strata seems broken too. almost all features break. SER causes lag instead of speed ups and changes no picture quality so not seeing a point to that either. can we also please get caustics in both eyes. all ray tracing works in both eyes but caustics now. i can see translucency and translucent reflection modes in vr just missing the caustics. works in left eye.