Power math node precision issue #101114

New Issue

Serge Lyatin · 2022-09-16T10:22:22+02:00

Serge Lyatin commented

2022-09-16 10:22:22 +02:00

System Information
Operating system: win10
Graphics card: 1050ti

Blender Version
Broken: 3.3.1 RC
Worked: 2.79b

Short description of error

Difference between 100 and 10^2 produced by Power node is not a zero. But it's correct in 2.79b version.

Exact steps for others to reproduce the error
In provided file unmute/mute Round math node to see a problem
math_precision_issue.blend

**System Information** Operating system: win10 Graphics card: 1050ti **Blender Version** Broken: 3.3.1 RC Worked: 2.79b **Short description of error** ![math_precision.jpg](https://archive.blender.org/developer/F13498629/math_precision.jpg) Difference between 100 and 10^2 produced by *Power* node is not a zero. But it's correct in 2.79b version. **Exact steps for others to reproduce the error** In provided file unmute/mute *Round* math node to see a problem [math_precision_issue.blend](https://archive.blender.org/developer/F13498647/math_precision_issue.blend)

Serge Lyatin commented

2022-09-16 10:22:22 +02:00

Added subscriber: @SergeL

Omar Emara commented

2022-09-16 11:08:59 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-09-16 11:08:59 +02:00

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

Omar Emara closed this issue

2022-09-16 11:08:59 +02:00

Omar Emara commented

2022-09-16 11:08:59 +02:00

I can confirm the issue. But Blender doesn't do anything special here besides calling the pow function, which may suffer from precision issues as you saw.
As for why it worked in 2.7, likely because it was constant folded by the compiler, which can't happen now because the values are passed as uniforms.
In any case, we don't handle such precision issues as bugs. Users should use expressions like x * x as an alternative.

I can confirm the issue. But Blender doesn't do anything special here besides calling the `pow` function, which may suffer from precision issues as you saw. As for why it worked in 2.7, likely because it was constant folded by the compiler, which can't happen now because the values are passed as uniforms. In any case, we don't handle such precision issues as bugs. Users should use expressions like `x * x` as an alternative.

Serge Lyatin commented

2022-09-16 12:20:52 +02:00

But why it has no problems with Geometry Nodes Power node? Same setup here works without artificial rounding.

Omar Emara commented

2022-09-16 12:38:02 +02:00

Geometry Node executes on the CPU, while shaders execute on the GPU. Both have a different implementation of the power function, and it seems the GPU implementation is less accurate.
Note that the implementation is done by the GPU driver and manufacturer, not by Blender, so we have no control over it.

Geometry Node executes on the CPU, while shaders execute on the GPU. Both have a different implementation of the power function, and it seems the GPU implementation is less accurate. Note that the implementation is done by the GPU driver and manufacturer, not by Blender, so we have no control over it.

Serge Lyatin commented

2022-09-16 12:51:12 +02:00

Thanks for clarification!

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Power math node precision issue #101114