Inconsistency between CPU and OptiX GPU when using OSL hash function #103328

New Issue

Alaska · 2022-12-19T03:47:28+01:00

Alaska commented

2022-12-19 03:47:28 +01:00

System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 4090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 527.56

Blender Version
Broken version: 3.5.0 Alpha, branch: master, commit date: 2022-12-18 20:06, hash: 50c7eb14f4
Worked: NA

Short description of error
When using the Open Shading Language "hash" noise function there is an inconsistency between the CPU and OptiX GPU implementation. The most noticeable is that the OptiX output is grey scale while the CPU implementation has colour.

CPU	OptiX

Exact steps for others to reproduce the error

In user preferences change your Cycles rendering backend to OptiX (requires a OptiX compatible GPU)
Download the attached blend file and open it.
Enter the rendered viewport and compare the results with CPU rendering and OptiX GPU rendering.

OptiX CPU OSL Hash Inconsistency.blend

**System Information** Operating system: Windows-10-10.0.22000-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 4090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 527.56 **Blender Version** Broken version: 3.5.0 Alpha, branch: master, commit date: 2022-12-18 20:06, hash: `50c7eb14f4` Worked: NA **Short description of error** When using the Open Shading Language "hash" noise function there is an inconsistency between the CPU and OptiX GPU implementation. The most noticeable is that the OptiX output is grey scale while the CPU implementation has colour. |CPU|OptiX| | -- | -- | |![OSL Hash CPU.png](https://archive.blender.org/developer/F14071572/OSL_Hash_CPU.png)|![OSL Hash GPU.png](https://archive.blender.org/developer/F14071574/OSL_Hash_GPU.png)| **Exact steps for others to reproduce the error** 1. In user preferences change your Cycles rendering backend to OptiX (requires a OptiX compatible GPU) 2. Download the attached blend file and open it. 3. Enter the rendered viewport and compare the results with CPU rendering and OptiX GPU rendering. [OptiX CPU OSL Hash Inconsistency.blend](https://archive.blender.org/developer/F14071576/OptiX_CPU_OSL_Hash_Inconsistency.blend)

Alaska commented

2022-12-19 03:47:28 +01:00

Added subscriber: @Alaska

Alaska commented

2022-12-19 03:47:36 +01:00

Added subscriber: @pmoursnv

Alaska commented

2022-12-19 03:47:36 +01:00

CC @pmoursnv

Patrick Mours commented

2022-12-19 12:31:51 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Patrick Mours commented

2022-12-19 12:31:51 +01:00

Yeah, this is expected behavior currently. Cycles doesn't implement multi-channel noise, so without changing that I could only implement the OSL intrinsics using single-channel noise that is then copied to all output components (hence why it looks black and white, R/G/B channels all contain the same noise value).
It shouldn't be difficult to implement by adjusting the noise functions in Cycles, just hadn't prioritized it. (It works with the CPU, since there OSL ships with its own implementation of all the intrinsics, whereas for OptiX they are implemented by Cycles)

Yeah, this is expected behavior currently. Cycles doesn't implement multi-channel noise, so without changing that I could only implement the OSL intrinsics using single-channel noise that is then copied to all output components (hence why it looks black and white, R/G/B channels all contain the same noise value). It shouldn't be difficult to implement by adjusting the noise functions in Cycles, just hadn't prioritized it. (It works with the CPU, since there OSL ships with its own implementation of all the intrinsics, whereas for OptiX they are implemented by Cycles)

Philipp Oeser removed the

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Inconsistency between CPU and OptiX GPU when using OSL hash function #103328