clamping and glossy roughness at glancing angles

[lacilaci]

I've noticed that using clamping can introduce some heavy darkening on glancing angles on walls if I want to use glossy material.(path cpu or opencl)
Without clamping or with high values the problem is much less visible but right at the corner it still gets dark.

This issue is not visible with bidir and with matte material (so I guess it's rough reflections with pathtracing).

Now I understand that very heavy clamping can make rendering look weird that's ok but in this case I really have to use high values or can't clamp it if I wand glossy material or coating.

Is there some workaround for this or is this a bug? I remember there was a similar issue with corona and I think fstorm too, where this darkening would appear on glossy walls etc. on glancing angles but it got solved in both renderers somehow.
I'm not sure if it's the same issue though.

[lacilaci]

I've noticed that using clamping can introduce some heavy darkening on glancing angles on walls if I want to use glossy material.(path cpu or opencl)
Without clamping or with high values the problem is much less visible but right at the corner it still gets dark.

This issue is not visible with bidir and with matte material (so I guess it's rough reflections with pathtracing).

Now I understand that very heavy clamping can make rendering look weird that's ok but in this case I really have to use high values or can't clamp it if I wand glossy material or coating.

Is there some workaround for this or is this a bug? I remember there was a similar issue with corona and I think fstorm too, where this darkening would appear on glossy walls etc. on glancing angles but it got solved in both renderers somehow.
I'm not sure if it's the same issue though.

here's the scene I've had the issue with.

[lacilaci]

It seems that matte material also shows this issue, when compared to bidir where it looks better.

I thought this is a material/shader issue but why isn't it showing with bi-dir?

[lacilaci]

Is this considered an issue? Or if not can someone tell me why is this not a problem?

I know I'm a bit annoying but this combined with bad denoiser are my biggest issues personaly with luxcore.