Bug Reflection Probes are not used with IndirectInstanced Rendering using the Deferred path

Hello,

Our project makes heavy usage of instanced rendering, but we've found that only the environment reflections set in the lighting panel have any effect on it. I've managed to eliminate it being a shader issue as using it in the scene as and letting Unity render it results in it correctly using the reflection probe's cubemap. I captured a frame in RenderDoc, using the same shader in the scene for both instanced and non-instanced rendering,it seems as though the instanced version uses either UnityBlackCube for the specular cubemap or the custom one set in EnvironmentReflection if it is set.

I've not found any documentation stating that reflection probes for IndirectInstancing isn't supported in URP, so it seems as though this must just be a bug.

 

I also just ran into this while using DrawMeshInstanced. I'm going to try a few different versions of Unity and see if it works in any of them. But currently I can't seem to get Reflection Probes to work on my instanced meshes.

 

We've actually migrated this project from HDRP to URP, which is why this problem came as a surprise as it was never an issue in HDRP. Presumably this means that it's doing extra work on the GPU to find this information, similar to what you've described with the Forward+ path?

 

As our project almost exclusively uses instanced rendering, we were exploring alternatives to being able to use reflection probes. We could get by using the Skybox mode in the environment reflections, however it seems as though updating the skybox at runtime seems to result in the renderer reverting to using UnityBlackCube for the environment cubemap. I've tried to find where people have solved this problem before and came across this post that had the same issue:
https://forum.unity.com/threads/reflections-dont-update-when-changing-skybox-at-runtime.529442/

Of course the reponse they had was to use reflection probes instead, but as that isn't an option for us with instanced rendering until some point in the future I'd like to know if it's possible to trigger an update to that environment reflection cubemap. I initially hackily experimented with inserting a ScriptableRenderFeature in the BeforeRenderingGBufferPass to overwrite the unity_SpecCube0, however this didn't yield any results and it seems as though that these properties are being internally set in the DrawRenderers call made in the GBufferPass.

Are there any other options for us to update the environment reflections map or are we simply stuck without being able to update them at runtime?

 

Thanks for the quick response, it's seeming as though this won't work either sadly. After looking at GlobalIllumination.hlsl and reading some of the shader values, both unity_SpecCube0 and unity_SpecCube1 have float4(-inf) and float4(inf) for their box bounds which if I'm reading the shader correctly will mean that their weight will be too high for the
_GlossyEnvironmentCubeMap to be used. I'm going to keep tweaking and see if there's something I'm missing but hopefully you'll be able to confirm whether I'm correct on this.

 

Update: I've copied the relevant parts of the GlobalIllumination.hlsl file into our own .cginc and have edited the Irradiance to just always read from the _GlossyEnvironmentCubeMap, this results in the behaviour that we were hoping from changing the skybox at runtime and will have to do until Forward+ supports reflection probes for instanced rendering

 

We were having a similar issue with using a dynamic skybox for a reflection map and noticed the calls to Graphics.DrawMeshInstanced/RenderMeshInstanced either used a default unity black cubemap if there was no light info baked into the scene (and Lighting/Scene/WorkFlow Settings/Recalculate Environment Lighting was off) or it used a default baked reflection map which never changed (RenderDoc is useful here to see which maps are being accessed by your shaders and how). We were able to work around this by setting unity_SpecCube0 in the material properties list for the draw calls as our use case only needed a single environment reflection map.