Differences between CPU and GPU with this Volumetric World Texture #52013

Closed
opened 2017-07-10 14:33:17 +02:00 by YAFU · 6 comments

System Information
Kubuntu Linux 14.04 64bits - GTX 960

Blender Version
Broken: 2.78c - From master hash ba256b32ee

Short description of error
Hi.
I get different results between CPU and GPU with the same configuration. In 2.78c with CPU I get a resulting black image. In Blender from master with CPU I get a better result, but apparently without being applied texture.
Volumetric World Texture.blend

Exact steps for others to reproduce the error
Open the scene in Blender and compare render results between CPU and GPU.

**System Information** Kubuntu Linux 14.04 64bits - GTX 960 **Blender Version** Broken: 2.78c - From master hash ba256b32ee5 **Short description of error** Hi. I get different results between CPU and GPU with the same configuration. In 2.78c with CPU I get a resulting black image. In Blender from master with CPU I get a better result, but apparently without being applied texture. [Volumetric World Texture.blend](https://archive.blender.org/developer/F657297/Volumetric_World_Texture.blend) **Exact steps for others to reproduce the error** Open the scene in Blender and compare render results between CPU and GPU.
Author

Changed status to: 'Open'

Changed status to: 'Open'
Author

Added subscriber: @YAFU

Added subscriber: @YAFU

Added subscribers: @brecht, @Sergey

Added subscribers: @brecht, @Sergey
Sergey Sharybin self-assigned this 2017-07-11 10:06:15 +02:00

The difference here is caused by different volume samplers used by CPU and GPU. The volume sampler in the file is set to MIS, which is only supported on CPU, GPU is using Distance sampling.

@brecht, couple of questions here:

  1. Shall those two methods converging to the same exact result with huge enough number of samples?
  2. Is it indeed a great idea to default to settings which are not supported by all devices?
The difference here is caused by different volume samplers used by CPU and GPU. The volume sampler in the file is set to MIS, which is only supported on CPU, GPU is using Distance sampling. @brecht, couple of questions here: 1. Shall those two methods converging to the same exact result with huge enough number of samples? 2. Is it indeed a great idea to default to settings which are not supported by all devices?

The two methods are supposed to converge to the same results, but they don't seem to, which is a bug.

Equiangular is much better than distance sampling if you have a (mostly) homogeneous world volume. So for CPU rendering it would not be a great default. Really the proper solution here is to improve the GPU implementation, I have some ideas on how to do that.

The two methods are supposed to converge to the same results, but they don't seem to, which is a bug. Equiangular is much better than distance sampling if you have a (mostly) homogeneous world volume. So for CPU rendering it would not be a great default. Really the proper solution here is to improve the GPU implementation, I have some ideas on how to do that.

Closed as duplicate of #50193

Closed as duplicate of #50193
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Reference: blender/blender#52013
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