# Epic's GPUlightmass

**URL:** <https://forums.unrealengine.com/t/epics-gpulightmass/139357>\
**Category:** Rendering\
**Tags:** unreal-engine\
**Created:** [March 5, 2020, 12:52pm UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357 "2020-03-05T12:52:56Z")\
**Posts on this page:** 20\
**Page:** 45

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**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [April 21, 2026, 5:37am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/895 "2026-04-21T05:37:04Z")

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There’s a similar issue posted above; is your emissive material Unlit? That will be ignored by GPULM.

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<div class="post-metadata">

**Author:** ![jeanzhaolu](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@jeanzhaolu](https://forums.unrealengine.com/u/jeanzhaolu)\
**Post date:** [April 21, 2026, 7:09am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/896 "2026-04-21T07:09:14Z")

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![image](https://d3kjluh73b9h9o.cloudfront.net/original/4X/c/8/b/c8bcb9ed1de412cb28c0a6a483b8960370248b67.jpeg)

Hi yujiang, I did read @anloarq’s post and replies,  
my emissive material is set to Surface, opaque, default lit,  
the mesh is set to static, emissive light source, lightmap - force surface.

and you can see the red ball is still not lighting up the surrounding objects after bake.

I have also uploaded the minimal project file in the previous post that you can try it. thank you

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<div class="post-metadata">

**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [April 21, 2026, 11:10am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/897 "2026-04-21T11:10:27Z")

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This is what you need:

 ![kqhCoeFoUY](https://d3kjluh73b9h9o.cloudfront.net/original/4X/c/b/c/cbc140eee83d9f54ca18bc17adebc95abaad0065.png)

Meanwhile, your cube’s UVs are not suitable for lightmaps as the UV islands are sticked to each other. I enabled Generate Lightmap UVs with a Min Lightmap Resolution of 64, darkened the light and the emissive source, and I got this:

 ![图片](https://d3kjluh73b9h9o.cloudfront.net/original/4X/b/a/7/ba74b876e197e82f96aacbd0ee0616714479b1e0.jpeg)

The denoiser hates lights that are too bright:

 ![图片](https://d3kjluh73b9h9o.cloudfront.net/original/4X/7/3/7/737ba7968c218ba89d1c0c0396892764e801a1c8.jpeg)

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<div class="post-metadata">

**Author:** ![jeanzhaolu](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@jeanzhaolu](https://forums.unrealengine.com/u/jeanzhaolu)\
**Post date:** [April 22, 2026, 12:07am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/900 "2026-04-22T00:07:44Z")

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aha that’s it, I only ticked the Emissive light source but over looked “Use Emissive for Static Lighting” under light mass advanced settings.

Its working now, thank you a million times!

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [April 22, 2026, 8:01am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/901 "2026-04-22T08:01:55Z")

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Hi, just wanted to ask if theres support for masked materials (on substrate)

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [April 27, 2026, 12:44pm UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/903 "2026-04-27T12:44:01Z")

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and also, wanted to ask what “volumetric lightmap quality” actually means, does it help with the deringing issue?

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**Author:** ![goldensyrupgames](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@goldensyrupgames](https://forums.unrealengine.com/u/goldensyrupgames)\
**Post date:** [April 28, 2026, 10:41am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/904 "2026-04-28T10:41:32Z")

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Hi, this patch is incredible. Thankyou for maintaining this.

I have a question - do you know what the usual source of the build hanging at 99% is, and if there is anything I can change to reduce it? The initial build process is pretty quick, the denoise and texture write at the end is quick, but it sits at 99% for about 8 minutes out of a 10 minute build. The only relevant logs just show a jump:

```auto
[2026.04.28-20.14.55:730][324]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes
[2026.04.28-20.14.57:323][324]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes
[2026.04.28-20.14.57:603][327]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes
[2026.04.28-20.22.22:901][734]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes
[2026.04.28-20.22.22:925][734]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes
[2026.04.28-20.22.23:109][736]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes
[2026.04.28-20.22.23:291][736]LogGPULightmass: Cached ray tracing scene is invalidated due to material changes

```

This doesn’t happen during “bake what you see either”.

Not a massive issue, but I’d love to reduce it if I can.

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<div class="post-metadata">

**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [April 28, 2026, 10:58am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/905 "2026-04-28T10:58:45Z")

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I conducted a test with a simple Substrate masked material:

 ![fqceaCm11c](https://d3kjluh73b9h9o.cloudfront.net/original/4X/5/6/b/56b182db7baae06ed2f645a605a74401be020689.png)

Both Blendable and Adaptive GBuffer are tested. GI bounces and shadows should work.

 ![ScreenShot00000](https://d3kjluh73b9h9o.cloudfront.net/original/4X/3/8/0/3800ff026cbae5c8a801250025120086c8d2ebc8.jpeg)  
 ![ScreenShot00001](https://d3kjluh73b9h9o.cloudfront.net/original/4X/4/f/7/4f7ebd1f484abf40ce6ba79a9803ae0c4deebbb2.jpeg)

VLM’s quality multiplier is simply a multipler on GI samples, because VLM has no denoiser support.

Deringing is indeed missing from GPULM. I’m actually studying it to see what’s a good way to implement it in GPULM.

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<div class="post-metadata">

**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [April 28, 2026, 11:01am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/906 "2026-04-28T11:01:00Z")

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Usually getting stuck at 99% means GPULM is processing VLM and its amount is huge.

For

```auto
LogGPULightmass: Cached ray tracing scene is invalidated due to material changes

```

It usually means you have something updating every tick invalidating the cache. Video textures could be one of them. It won’t affect the quality of the bake.

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<div class="post-metadata">

**Author:** ![goldensyrupgames](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@goldensyrupgames](https://forums.unrealengine.com/u/goldensyrupgames)\
**Post date:** [April 28, 2026, 11:04am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/907 "2026-04-28T11:04:10Z")

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> [@yujiang.wang](#):
>
> VLM

Okay thanks, this must be it. It’s before denoising - denoising is pretty quick. Overall this is much quicker than CPU lightmass so I’ll just live with it. Thanks again for all this - you’re keeping baked lighting alive.

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [May 3, 2026, 8:12am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/908 "2026-05-03T08:12:36Z")

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weird that it didnt work for me, will double check later  
also REALLY great to hear any actual news on features like VLM deringing!

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [May 5, 2026, 10:17pm UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/909 "2026-05-05T22:17:44Z")

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i know this is a stretch but, any possible updates for movable objects?  
for example, im working on this scene that has a moving train, but GI is leaking into the train which makes it unusually bright, i was wondering if there was any option to DISABLE the VLM GI on the train

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<div class="post-metadata">

**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [May 6, 2026, 4:15am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/910 "2026-05-06T04:15:18Z")

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set Lightmap Type to Force Surface should attach a lightmap to the movable actor. though it seems like it is bugged in the editor now - moving the actor will invalidate the lightmap. but from the code, the lightmap will only be invalidated inside the editor. you can try it in a packaged build and see if it works

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<div class="post-metadata">

**Author:** ![brisck1](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@brisck1](https://forums.unrealengine.com/u/brisck1)\
**Post date:** [May 8, 2026, 12:04am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/911 "2026-05-08T00:04:31Z")

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Hey @yujiang.wang I’m having issues in Unreal 5.7.4 with both the stock GPULM and your updated version (GPULM-5.7.4.tgz extracted into the root UE\_5.7 folder).

I have a very simple test scene with a static skylight, lightmass importance volume and a volumetric lightmap density volume and some test content (a small landscape, lightmapped static meshes and volumetric lightmapped meshes).

For some reason in UE57, when baking this scene, the volumetric light probes do not bake at all and the meshes that rely on VLM remain black. I can sometimes get them to bake by moving something in the scene and hitting bake again, but that’s kinda annoying process, especially for large levels.

The other issue is that the Landscape doesn’t seem to bounce light at all. Any ideas on what might be going wrong?

Here’s a link to my test project: [https://drive.google.com/file/d/1OQJKUQ1gW9eVx990fbywcNyoHq8T2m0P/view?usp=sharing](https://drive.google.com/file/d/1OQJKUQ1gW9eVx990fbywcNyoHq8T2m0P/view?usp=sharing)

 ![{15ACC32F-C9CF-40AE-943F-BAB877476925}](https://d3kjluh73b9h9o.cloudfront.net/original/4X/5/8/0/580caaa7f43b3b3214be9a013993e138fa068a07.jpeg)

 ![{7397C499-878D-4E64-BFD9-31607C0A8153}](https://d3kjluh73b9h9o.cloudfront.net/original/4X/6/2/f/62fca7a5cda2403ee0e74b987ac923cc271ef0cd.jpeg)

Edit: Interestingly, when setting the Landscape to use Nanite, I get actual bounce light… (doesn’t fix the VLMs not baking properly though)

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<div class="post-metadata">

**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [May 8, 2026, 4:25am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/912 "2026-05-08T04:25:12Z")

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Could no repro on my computer; bake succeeded on the first attempt and Nanite is disabled for landscape:

 ![ScreenShot00001](https://d3kjluh73b9h9o.cloudfront.net/original/4X/1/1/3/1131f20431089e7c4429ec86605b124c695bdcb5.jpeg)  
 ![ScreenShot00000](https://d3kjluh73b9h9o.cloudfront.net/original/4X/9/8/b/98b99d08c27e692190eb10974ad3b1c9e0b55663.jpeg)  
 ![wquVk8iizQ](https://d3kjluh73b9h9o.cloudfront.net/original/4X/8/0/c/80cab6aea83cc0864c60769a8e917dd06e892e1f.png)

I would suggest you delete all \_BuiltData.uasset and clear derived data cache.

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<div class="post-metadata">

**Author:** ![brisck1](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@brisck1](https://forums.unrealengine.com/u/brisck1)\
**Post date:** [May 8, 2026, 6:30pm UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/913 "2026-05-08T18:30:03Z")

</div>

Thanks for looking into this, and the prompt response. I tried deleting the \_BuiltData.uasset data and clearing the derived data cache with no change. Strange. I wonder if i’ve incorrectly installed the binaries somehow? Do you have detailed instructions somewhere? I assumed I just needed to extract them to the UE57 folder and overwrite existing files. I might try compiling from the source code next.

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [May 9, 2026, 1:00am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/914 "2026-05-09T01:00:20Z")

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it doesnt work for me, im relying on a bunch of planes with a dynamic parameter for each one to do a shelltexturing effect, but on stationary lights it treats the planes like they’re not masked

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [May 9, 2026, 1:13am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/915 "2026-05-09T01:13:38Z")

</div>

going from primitive data parameters to regular scalar parameters has fixed the issue, although its insanely frustrating

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<div class="post-metadata">

**Author:** ![stamisme](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@stamisme](https://forums.unrealengine.com/u/stamisme)\
**Post date:** [May 9, 2026, 1:20am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/916 "2026-05-09T01:20:50Z")

</div>

also one question i have is, can glass be baked? at the moment my glass surfaces are movable which doesnt look that good due to the low VLM density

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<div class="post-metadata">

**Author:** ![yujiang.wang](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@yujiang.wang](https://forums.unrealengine.com/u/yujiang.wang)\
**Post date:** [May 10, 2026, 8:25am UTC](https://forums.unrealengine.com/t/epics-gpulightmass/139357/917 "2026-05-10T08:25:42Z")

</div>

# Release 5.7.4 2026.05.10

[https://downloads.luoshuangfw.io/gpulm-releases/GPULM-5.7.4.7z](https://downloads.luoshuangfw.io/gpulm-releases/GPULM-5.7.4.7z)  
[Back to release list](https://forums.unrealengine.com/t/epics-gpulightmass/139357/667)

- Add support for custom primitive data

 ![LLG2r7FyX4](https://d3kjluh73b9h9o.cloudfront.net/original/4X/7/9/8/798d73fb7c9fb00a40209bf1425cd6c0e1af81ba.png)

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