Ray Tracing Overview - Unreal Engine 4.22 Preview

We have prepared a document to provide additional information for the ‘early access’ ray tracing feature as it currently exists in the Unreal Engine 4.22 Previews.

This document is targeted specifically at designers and visualization artists in the Architectural Visualization industry, although much of the information will be applicable to anyone interested in ray tracing in the Unreal Engine.

You can find the latest documentation to get started here.


Removed old PDF from the preivews.

Thanks for the document. It is very concise, so really good as quick guide.

One question that could be handled as FAQ and which many are looking to know is: Will multi-GPU get support with RT? We know that currently the engine has no multi-GPU support.

Great PDF, super useful. Thanks Stephen.

Will RTGI Denoiser enhance with the stable release of UE4.22 or will maintain its current state?
I think these diffuse black dots (+ ghosting) in darker areas are a drawback to use GI.

PDF is great and clear, thanks!

There are several problems

  1. When can Mask materials be supported? Existing Msak materials, such as vegetation, are heavily flickering in DXR Shadow, which means that Mask objects cannot be used in DXR scenarios, that is, most existing projects are difficult to actually use DXR.

  2. The support of Landscape and HISM, Foliage System, although we know from many places that these objects do not seem to be supported in 4.22, will we have a hybrid alternative? For example, let CSM Shadow complete the content that DXR does not support. Otherwise, these unsupported modules under DXR rendering have no good processing method at all. Even the early preview version of 4.22 can not be applied to many projects.

  3. Can GI and AO be used separately? When we first saw the preview version, we were shocked by AO, so excellent performance and effect performance that we were waiting for the follow-up RTGI, but after the emergence of RTGI, we faced worse performance and noise reduction performance, so we hope to use AO alone instead of using GI with unsatisfactory performance and effect, but after the launch of GI, it seems that GI and AO did not. Can any way be used separately?

  4. With regard to noise reduction devices, in the initial demonstrations of NVIDIA, and even in many DXR Demos made in Unreal, there are excellent performance of noise reduction. Perhaps this is based on AI noise reduction of RTX graphics cards? But our existing DXR does not seem to have this performance of noise reduction. When moving, the noise point is very obvious. This is obviously not from NVIDIA’s AI noise reduction. Will it be supported by AI noise reduction in the future?

Thank you in advance for your answer!

Could be useful for beginners but for example there is no info about how to use denoiser commands, what they do etc. like r.GlobalIllumination.Denoiser.HistoryConvolution.KernelSpreadFactor, r.GlobalIllumination.Denoiser.HistoryConvolution.SampleCount, r.GlobalIllumination.Denoiser.ReconstructionSamples, r.GlobalIllumination.Denoiser.TemporalAccumulation

Any plans to apply the denoiser to the path tracer? Go on, you know you want to.

And is there some kind of buffer UV issue? I’m getting outlines on everything:

Just curious… how is it setup ambient occlusion at that scene? Is it contributing to the outline?

Default raytracing settings and the rolling ball template produce the effect for me. I turned on skylight tracing for that screenshot but it’s more pronounced in the default configuration. Running the preview rather than the dev branch.

There’s no outline shader, nothing is stenciled, so it must be some raytracing pass.

It would be good if you could add something addressing raytracing + VR support to the FAQ. Where it stands in 4.22, how the plans are for the future.

We used this document to test Raytracing yesterday (we are an architecture office)…and OMG this is awesome. The potential is huge.

Thank you for this doc! Very appreciated!


Just wondering, are there any extra parameters to enable to ensure the denoiser works? Currently it seems to have no effect regardless of whether if its enabled or not. Based on the PDF, it suggests that 1 SPP should be enough with a Sky light, but the shadows I am getting are still incredibly noisy.

Stephen Ellis, do you have to run the packaged app with the -dx12 option or not?

Hi there.

I unfortunately do not seem to be seeing the “Ray Tracing” option appearing under View Mode :frowning: :frowning:

I have followed the PDF to the letter as far as i can tell:

  • My system is running Windows 10 1809 (17763.316)
  • I have added “-dx12” to the Shortcut for Unreal 4.22 Preview
  • I have confirmed it is running in DX12 mode by looking into the Output Log and seeing the following string: “LogD3D12RHI: Chosen D3D12 Adapter Id = 0”
  • In Project Settings, I have enabled “Ray Tracing”, and “Support Compute Skincache”
  • I have an Nvidia 2080 FE

I have closed and restarted several times, always launching from the -dx12 shortcut. It all seems to have gone well apart from the fact i can’t see Ray Tracing option in the View Mode menu.

I have tried running commands from the Output Log as well, it showed that Ray Tracing was already turned on i.e r.RayTracing = “1”…

Any ideas please? I’d really like to give this a go.

Another idea would be at least one example scene people could download just so they can verify that it is all indeed working and plugged in correctly.


Not sure to spam here, but in case you can delete post. Here I show how UE4.22 Preview 4 is working.


  1. Try my demo. Press on shortcut, not exe file. When “game” starts, press and hold “D” on keyboard to see with or without GI.
    In case you see nothing in 2-3 seconds, close with Alt+F4. For first time there are always graphic problems. My PC specs: AMD 2200G, RTX 2070.
  2. You must use execute console programms in blueprint editor.

Yes, as of 4.22 Preview 4, you need to run your packaged build using a shortcut with the -dx12 parameter, just like you’d launch the editor.

Note that you also need to use this option when running a standalone preview from within the editor… you can set this up in Editor Preferences:

Other tips here:

has anyone been able to get translucency working?

I’ve made a completely transparent sphere but it’s still casting a solid shadow.

Same issue in my project with RayTracing.Reflections

Is RTGI fonctionnal in preview4?
It seams RTGI has no effect if RTAO is desactivated… strange…