Cycles smoke render differs on CPU from GPU #54577

New Issue

Alex Murray · 2018-04-12T03:29:52+02:00

Alex Murray commented

2018-04-12 03:29:52 +02:00

System Information
Tested on multiple systems:

Windows 10

AMD Threadripper 1950X
NVidia GTX 580

Windows 10

AMD Radeon RX 480

Windows 10

NVidia GTX 1060 6GB

Blender Version
Broken: 2.79 5bd8ac9
Worked: Not sure

Short description of error
Rendering smoke using Cycles on the GPU produces noticeably different output than when rendering the same frame on the CPU.

The difference is most noticeable at the edges of smoke or if the smoke is thin. The GPU produces much noisier results than the CPU.

Exact steps for others to reproduce the error

Download attached .blend file. Press alt+A to start animation.
Wait until you reach frame 60 or so.
Press alt+A to stop animation again.
Render a frame on the CPU
Render a frame on the GPU
The GPU frame will be much noisier than the CPU frame.

smoke-testing.blend

**System Information** Tested on multiple systems: 1) Windows 10 ``` AMD Threadripper 1950X NVidia GTX 580 ``` 2) Windows 10 ``` AMD Radeon RX 480 ``` 3) Windows 10 ``` NVidia GTX 1060 6GB ``` **Blender Version** Broken: 2.79 5bd8ac9 Worked: Not sure **Short description of error** Rendering smoke using Cycles on the GPU produces noticeably different output than when rendering the same frame on the CPU. The difference is most noticeable at the edges of smoke or if the smoke is thin. The GPU produces much noisier results than the CPU. **Exact steps for others to reproduce the error** 1) Download attached .blend file. Press alt+A to start animation. 2) Wait until you reach frame 60 or so. 3) Press alt+A to stop animation again. 4) Render a frame on the CPU 5) Render a frame on the GPU 6) The GPU frame will be much noisier than the CPU frame. [smoke-testing.blend](https://archive.blender.org/developer/F2665194/smoke-testing.blend) ![2.png](https://archive.blender.org/developer/F2665200/2.png)

Alex Murray commented

2018-04-12 03:29:52 +02:00

Added subscriber: @TheComet

blender-admin commented

2018-04-12 03:29:52 +02:00

#83170 was marked as duplicate of this issue

Ray molenkamp commented

2018-04-12 03:39:43 +02:00

Added subscriber: @LazyDodo

Ray molenkamp commented

2018-04-12 03:39:43 +02:00

2.79 5bd8ac9 is quite old, please try 2.79b and/or a build from http://builder.blender.org and see if the problem persists.

2.79 5bd8ac9 is quite old, please try 2.79b and/or a build from http://builder.blender.org and see if the problem persists.

Mai Lavelle commented

2018-04-12 07:44:08 +02:00

Added subscriber: @MaiLavelle

Mai Lavelle commented

2018-04-12 07:44:08 +02:00

Pretty sure this is the difference between decoupled volume sampling on the CPU vs regular volume sampling on GPU (decoupled isn't supported on GPU). Doesn't look like a bug to me.

Brecht Van Lommel commented

2018-04-12 07:59:17 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2018-04-12 07:59:17 +02:00

Changed status from 'Open' to: 'Resolved'

Brecht Van Lommel closed this issue

2018-04-12 07:59:17 +02:00

Brecht Van Lommel self-assigned this 2018-04-12 07:59:17 +02:00

Brecht Van Lommel commented

2018-04-12 07:59:17 +02:00

That's correct, you can change the volume sampling method to Distance in the material if you want the same result on the CPU. Equiangular and multiple importance sampling reduce noise a lot when there are lights inside or near the volume, but increase it when that's not the case.

Alaska commented

2020-11-29 04:01:48 +01:00

Added subscribers: @valera-8, @Alaska

Alaska commented

2020-11-29 04:02:05 +01:00

Removed subscriber: @Alaska

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Cycles smoke render differs on CPU from GPU #54577