Reflection captures and lightmaps

Development Rendering
1

Hi, I have noticed UE4 multiplies the reflection captures with lightmaps. Why is it doing that? Is there a way to disable?

This breaks SSR since reflection captures will be much darker, dynamic objects stand out since their lighting is very different from lightmaps, etc…

2

Are you sure its the SSR and not the shader setup?

3

This is what I’m talking about:

In ReflectionEnvironmentComputeShaders.usf:


				#if USE_LIGHTMAPS
					// We have high frequency directional data but low frequency spatial data in the envmap.
					// We have high frequency spatial data but low frequency directional data in the lightmap.
					// So, we combine the two for the best of both. This is done by removing the low spatial frequencies from the envmap and replacing them with the lightmap data.
					// This is only done with luma so as to not get odd color shifting.
					// Note: make sure this matches the lightmap mixing done for translucency (BasePassPixelShader.usf)
					//Sample.rgb *= IndirectIrradiance;
				#endif

I just changed it using the source, but I’m wondering why the devs think this is a good idea…

For example, let’s say you a cube under a bridge where very little indirect lighting hits it which will result in a dark lightmap.

However that cube should reflect the sky in full brightness even though it doesn’t get a lot of indirect lighting.

Another thing is that the docs say: “The cubemap reflection is mixed together with the lightmap indirect specular based on how rough the material is”
However, the code does not take roughness into account…