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Raytraced reflections don't have shadows or GI

Simple scene with a HDRI skylight and raytracing enabled. The sphere reflection of the scene has no shadows or GI. Path tracer shows how it should look.

Have I missed a switch somewhere or is this broken?

UE 4.25.3

ue_raytrace_refl_error.jpg

Shadowing from direct lights just works, it has an option in the post process. Skylight contribution is disabled by default in reflections, it can be enabled though.

r.RayTracing.Reflections.RayTraceSkyLightContribution = 1

You’ll need to set the skylight raytracing samples pretty high in order to get a reasonable result (I used 32 for this SS)

I may be wrong but I don’t think raytraced GI is supported for reflections, the performance penalty might be too high to allow it.

Yes that works for shadows. I’m pretty new to Unreal so didn’t even realise there are so many hidden console vars thanks!

So I went through all the vars in 4.26 but couldn’t get the indirect lighting showing up in reflections, so looks like that isn’t currently supported as you say. Probably not a showstopper for my project though would be nice, FPS isn’t the issue for me as much as quality is.

Experimenting further, having issues with roughness. As the roughness increases it deviates more and more from the path tracer. At 0.8 is appears to be ignoring secondary reflections altogether.

Have set everything I can find, e.g. r.RayTracing.Reflections.MaxRoughness = 1 and r.RayTracing.Reflections.SamplesPerPixel = 32 but nothing seems to help.

(sorry gifs look horrible but should get the point across)

Roughness 0.05

ue_raytrace_refl_roughness_005.gif

Roughness 0.5

ue_raytrace_refl_roughness_05.gif

Roughness 0.8

ue_raytrace_refl_roughness_08.gif

Can’t seem to reproduce your problem in 4.26p3. It may be a bug that got fixed, unfortunately I can’t test on 4.25 atm.

Left to right: 0.8, 0.5, 0.05 roughness

Result isn’t perfect but I attribute that to lack of GI in reflections, otherwise it seems fine.

The lack of skylight shadows in your last screenshot leads me to believe this may be an issue with the skylight, not reflections.

Forgot to mention I did those roughness tests in 4.26p3

I don’t think this is a skylight specific problem, the SL cube in my example is emissive and it doesn’t reflect correctly either.

Some more tests (4.26p3)

Emissive cube, sphere roughness 0.5, sphere roughness 0.8, cube basic mat, floor roughness 0.8

UE raytracing:-

Path tracer:-

and if I turn off the skylight

UE raytracing:-

Path tracer:-