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Blender Cycles Render results looking different at the BMW MikePan Benchmark File.
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System Information
Operating system and graphics card
Windows 7 64 bit
AMD Phentom 2 X6 1100T
AMD Radeon HD 6950 2GB VRam

Blender Version
Broken: (example: 2.69.7 4b206af, see splash screen) 2.69.10 5c8d5c7
Worked: (optional) 2.69 Release version

Short description of error
When you render the BMW-MikePan Scene you get with the new build a different result on the headlight of the car.
General you could look through the glass, now with these build you get 100 percent reflection.

Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps
I used the BMW-MikePan.blend from the 2.61 Demo Files.

1.You start blender

  1. Open the Scene
  2. Go to Viewport Rendering or Render ( same problem)

Event Timeline

David Schrott (thelasthope) created this task.
David Schrott (thelasthope) raised the priority of this task from to Needs Triage by Developer.

I don't see any difference between 5c8d5c7 and the 2.69 release, on OS X and Windows 7 64 bit.

Can you attach a screenshot that shows the difference? Which CPU model do you have?

Brecht Van Lommel (brecht) triaged this task as Needs Information from User priority.Feb 12 2014, 6:50 PM

The same result you get also with 5c8d5c7

When you look at my System Information you see my CPU
AMD Phentom 2 X6 1100T

@Sv. Lockal (lockal), any idea what might be causing this? I suspect the SSE/AVX optimizations are involved.

I also can't reproduce this problem. I don't see any connection with SSE optimizations. Front headlights are just simple mesh objects with no textures.

By the way, I don't recognize this BMW-MikePan variant. The original file from blenderartists has different headlights material and bmw.blend from SVN testfiles has different reflection on the front window.

Dull lights remind me of recent indirect clamping by Dingto (rBe29a45b396ccf507d858ec4afc301bdaf816b328)
with this warning:

WARNING: This breaks backwards compatibility. If you had Clamping enabled in an old file, you must re-enable either Direct/Indirect clamping or both again.

Maybe this BMW.blend modification has some kind of clamping, which made this file incompatible?

Also, both renders have almost no noise, so I guess this modification has some kind of clamping.

@David Schrott (thelasthope): Next time pls upload the .blend file directly for everyone here, that's easier, especially since there are some different versions of it.

I found the problem @Brecht Van Lommel (brecht) and @Sv. Lockal (lockal)
In this particular file version of the BMW, the Glass shader has an IOR of 1.0.

In 2.69, we clamped the IOR to "1.0 + 1e-5f", now it's just "1e-5f". Setting the nodes glass IOR to 1.001 fixes the issue and converges to the same result in current master.

Therefore I would not consider this a bug and rather mention this in the release logs, among my clamping backwards compatibility change.

@Thomas Dinges (dingto): Sorry for that, it is the first time i report a bug.

Did you need still the blend file. When yes tell me.

It should be fine now, we know the cause of this. :)

Oh, well this should actually keep working, it's probably a division by zero somewhere, let me see.