Original Unreal Engine 4 opening post updated for UE 4.19 to 4.27 which will be updated to UE 5 later
Limitations:
- Written in CUDA so NVIDIA only.
- Supports all 4 standard lights (point, spot, directional and sky)
- However stationary skylight is not supported so if you have one in your scene it will still be baked since it is treated as a static one
- Advanced lighting features such as soft shadows (SourceLength and SourceRadius) and IES are not respected when calculating indirect lighting. However you may still see some effect of them since their direct lighting is calculated on CPU
- According to some tests the direct lighting is low quality sometimes because Lightmass quality level is set to “Preview”. While this problem is actually irrelevant to GPULightmass, you’ll probably want to set the quality level to “Production” to avoid such kind of mysterious problems.
- Supports baking of standard surface lightmaps, volumetric lightmaps (also with faster voxelization), and sparse volume lighting samples
- Lightmass parameters and quality settings specified in the editor are ignored except for Num Indirect Lighting Bounces
- Current the number of samples (quality settings) is hardcoded in the program and you cannot change it since I haven’t found an reliable way to expose them to the user
- AO Mask generation is not supported
- GPULightmass should work with Swarm distributed rendering naturally as long as you’ve correctly set up the environments on all machines. (esp. a sufficiently new NVIDIA driver)
Useful Tips:
Lighting build skipped because of ForceNoPrecomputedLighting set to true when it is actually false
- GPULightmass uses Brute Force as its Primary GI Engine and some form of radiosity caching as its Secondary GI Engine, which is very similar to vray.
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Brute force is much more accurate than Irradiance Caching (Lightmass’s primary GI engine) but it is also slower. It is also more sensitive to lightmap resolution since it actually calculates each lightmap texel, while irradiance caching is more or less resolution independent. You may want to tune down your lightmap resolutions firstly then slowly tune them up when working with GPULightmass.
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Comparison of Brute Force vs Irradiance Caching:
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Since adaptively placing more samples around corners (known as Retrace in vray) hasn’t been implemented you may see sploches.
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- You can use command line to launch the editor and bake lighting to save GPU resources for GPULightmass, especially video memory.
- Engine/Binaries/Win64/UE4Editor-Cmd.exe “path o\your\project\yourproject.uproject” -run=resavepackages -buildlighting -allowcommandletrendering -map=/Game/Maps/MyMap.umap
- Remember to replace Content with Game in the umap path
- It is recommended to change Windows TDR settings to prevent the GPU from being timed out (unspecified launch failure and other Error crashes) under heavy workload
- See GPU Lightmass Global Illumination in Unreal Engine | Unreal Engine 5.4 Documentation | Epic Developer Community
- A value of 300 is good
- You need to reboot your system
- Windows Update may reset this setting, so check again if you have problems after updating
- Some stats:
- A scene having 30M triangles and 150 1K lightmaps requires 7GB video memory and ~3hrs to bake on a GTX1080
Change Log:
[04/16/2018] Fixed attenuation calculation of spotlights
[04/14/2018] Further improved the adaptive hemisphere sampler to suppress visible artifacts
[04/14/2018] Fixed issues with sparse volume lighting samples and masked materials
[04/14/2018] Fixed a bug inside the adaptive hemisphere sampler. The number of samples is also raised. Now GPULightmass runs at Ultra High settings by default, which is a little bit overkill for most scenes.
[04/13/2018] Added support for sparse volume lighting samples
[04/13/2018] Fixed a bug which prevents GPULightmass from running on cards that are older than GTX10XX
Known Issues:
- Ray hit rejection by LOD/HLOD hasn’t been implemented and you may see black splotches where lower LOD meshes poke out.
How to Get the Best out of GPULightmass:
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Currently GPULightmass uses all emissive materials in baking regardless of ‘Use Emissive in Static Lighting’ option. If you see sparkles they are probably from some small bright emissive sources (especially, small LED panels in kitchen). You’ll want to use the LightmassReplace material node or set the EmissiveBoost to zero to remove them for GPULightmass. Starting from 4.20 GPULightmass respects ‘Use Emissive in Static Lighting’ option. However, t****he idea is to not use any small & bright emissive light sources in GPULightmass. If you want to get rid of sparkles, you can also try tuning down ‘FireflyClampingThreshold’.
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GPULightmass uses ‘Two Sided Emulation’ on all two-sided materials which could be the reason why people are seeing darken environments and light leaks. Currently the workaround is to turn off two-sided on the problematic materials.