Hi,
I've noted that, using a glossy material, the roughness values have impact on rendering speed (samples/sec).
With extreme low roughness values you get slower rendering speed than medium one.
For example.
Roughness 0.001
Roughness 0.1
I always expected the reverse...more roughness..more time to sample the result.
Roughness value and rendering speed
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Please upload a testscene that allows developers to reproduce the problem, and attach some images.
Please upload a testscene that allows developers to reproduce the problem, and attach some images.
Re: Roughness value and rendering speed
Have you tried on CPU ?
This may be consequence of GPU being faster at tracing "near" (aka coherent) rays (at low roughness, most rays are fired in about the same direction).
P.S. this effect is also a consequence of the very simple scene, I doubt you can notice this effect on a normal scene.
Re: Roughness value and rendering speed
Tried and it render at the same speed.
Actually it seems that it envolves also a "normal scene".
Look at this (GPU viewport render)
Roughness of the external light fixture shell: 0.05
Roughness: 0.001 (the lower value possible)
Consider also that, in this scene, it crashed blender after some seconds of viewport rendering when I use that low roughness value
Re: Roughness value and rendering speed
10x times slower, no, that is not normal. Sometime, GPU handles errors like NaNs or memory fault very slowly. If you post a test scene I can check.
Re: Roughness value and rendering speed
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Re: Roughness value and rendering speed
it seems that the glossy coating material is not affected by this issue.
with 0.001 as roughness, it renders fast as higher values.
with 0.001 as roughness, it renders fast as higher values.
Re: Roughness value and rendering speed
I'm testing the scene and the problem seems to affect only the combination of GTX980 with Optix on my hardware. Every other combination (i.e. GTX980 without Optix and RTX2070 with/without Optix) works fine. This looks like an Optix bug.
Do you have a GTX 9xx GPU ?
It starts to be pretty clear that, while Optix is supposed to work on old GTX GPUs, it is both slower than my BVH code and has problems. We will change the default behavior as soon as B.Y.O.B. is back in town and Optix will be used only on RTX GPUs.
In the mean time, you can just disable Optix in BlendLuxCore preferences and it should fix the problem.
P.S. this is standard corporate programmate obsolescence at work
Re: Roughness value and rendering speed
I have a GTX1070.
Tried disabling Optix and no more problem with roughness.
With Optix on, Disney or Glossy Coating (with a matte as base) material renders fine.