Different render output on different systems/possibly regression
Open, ConfirmedPublic

Description

System Information
Windows and Debian Linux

Blender Version
Broken: 2.78
Worked: 2.74

The rendered image is significantly different on different platforms.
However, it seems that the output of Version 2.74 on Debian Linux is quite similar to the Windows 2.78 output, so this might be a regression.

The transparent material uses Glass (GGX), Transparent and Translucent shaders. The surrounding copper object uses Fresnel and Glossy (GGX).
I may be able to strip this down to a simpler scene this evening.

Details

Type
Bug
Sergey Sharybin (sergey) triaged this task as "Incomplete" priority.Oct 21 2016, 12:53 PM

Please always attach .blend file which demonstrates the issue.

It took me actually two hours to strip down the 700MB blend file I am currently working on to this one. I will also post another comparison picture as soon as rendering is finished.

bug6.blend

It is worse than expected.

Sergey Sharybin (sergey) raised the priority of this task from "Incomplete" to "Needs Triage".Oct 22 2016, 12:58 PM
Sergey Sharybin (sergey) triaged this task as "Confirmed" priority.Oct 25 2016, 4:34 PM

Can confirm the difference and it's caused by either difference in libc version or in compiler. For example, glibc211 and glibc219 builds are giving different results. Doing local build with gcc-5.4 and gcc-6 both gives same results as libc219 builds from buildbot.

Disabling QBVH makes results closer to match, but there is still some difference (but AFAIR also causes difference between CPU and GPU).

Needs some deeper investigation to see where exactly the issue is coming from.

@Brecht Van Lommel (brecht), can you think of some trickery here to help us troubleshooting?

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