Cycles SSS node: Passes output failed when scale=0 #42818
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Reference: blender/blender-manual#42818
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System Information
Windows 8.1 64bit | GTX680
Blender Version
Broken: 2.72.2 367204a
Short description of error
In SSS node, when setting scale=0, Color is still visible in Preview, but failed as passes.
Exact steps for others to reproduce the error
Open attached file, then F12.
SSS.blend
Thanks for checking.
Changed status to: 'Open'
Added subscriber: @ZhangYu
Added subscriber: @mont29
Not quite sure there is any bug here (kind of makes sense to me that with zero scale, you get noting from sss passes...). Sergey would know!
@mont29, Actually, Something strange is: The "Combined" pass shows exactly what's seen in Preview window, for Combined pass, it's the combination of Diffuse, Glossy, Transmission, SSS.... as mentioned in wiki , but when trying to make Combined pass by combining all passes (including SSS), the result shows that there are no SSS there. But the Combined pass has it, which hardly makes sense, I suppose.
I'd say, combined pass wouldn't have SSS at all, I'd even guess SSS part of code is completely skipped in this case. Also, that wiki page is most likely not really up to date? Does not mention SSS passes at all even. Anyway, I'm years-light far from being cycles expert, let's see what say people who know what they are talking about. ;)
Sure. :) BTW, I did some tests. And I can confirm, from user's aspect, that the rule mentioned on wiki still works even with SSS with scale > 0
For better understanding:
scale=0:
scale=0.3:
Pass_Combine.blend
@mont29 I think you may right about it being "skipped" in compositor. It makes sense to me. If it is not a real bug, then there should be some updates on Wiki for such case, to explain why "Combined" pass and Preview result don't follow that rule.
Internally BSSRDF (SSS BSDF) with size of 0 gets replaced with diffuse BSDF, so it's evaluation happens much faster.
Now, pass accumulation was ignoring such a replaced BSDFs, leading to wrong results. Think it's totally reasonable to make it so SSS passes does not depend on internal optimization and gives the same results with zero and near-to-zero sizes.
Will commit fix soon.
As for the diagram and missing mention of SSS in the documentation, do you mind firing a bug report to #Documentation project?
This issue was referenced by blender/blender@7366283c01
Changed status from 'Open' to: 'Resolved'
Closed by commit blender/blender@7366283c01.
This issue was referenced by blender/cycles@f3b3908d46