Unexpected behavior when combining Color Attributes with White Noise Texture #103255

New Issue

Elias · 2022-12-16T03:02:38+01:00

Elias commented

2022-12-16 03:02:38 +01:00

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 517.00

Blender Version
Broken: version: 3.4.0, branch: blender-v3.4-release, commit date: 2022-12-06 18:46, hash: a95bf1ac01
Worked: (newest version of Blender that worked as expected)

Short description of error
Plugging in an object's color attributes into a white noise texture yields an unexpected banding pattern, even if every vertex shares the same exact color.

Exact steps for others to reproduce the error

Select the default cube and go into Vertex Paint mode, which will create a new color attribute.
(notice how each vertex is pure white)
Create a material for the cube.
Add a White Noise Texture node, and plug the Value or Color into the Surface of the Material Output
Add a Color Attribute node, and connect it to the Vector of the White Noise Texture
Notice the banding pattern

Expected result would be identical to plugging in a solid white RGB node.

Actual results:

Blend file:
color attribute white noise bug.blend

**System Information** Operating system: Windows-10-10.0.19044-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 517.00 **Blender Version** Broken: version: 3.4.0, branch: blender-v3.4-release, commit date: 2022-12-06 18:46, hash: `a95bf1ac01` Worked: (newest version of Blender that worked as expected) **Short description of error** Plugging in an object's color attributes into a white noise texture yields an unexpected banding pattern, even if every vertex shares the same exact color. **Exact steps for others to reproduce the error** 1. Select the default cube and go into Vertex Paint mode, which will create a new color attribute. (notice how each vertex is pure white) 2. Create a material for the cube. 3. Add a White Noise Texture node, and plug the Value or Color into the Surface of the Material Output 4. Add a Color Attribute node, and connect it to the Vector of the White Noise Texture 5. Notice the banding pattern Expected result would be identical to plugging in a solid white RGB node. ![blender_xie74Qdtg9.png](https://archive.blender.org/developer/F14060986/blender_xie74Qdtg9.png) ![blender_VJaaspd2iU.png](https://archive.blender.org/developer/F14060984/blender_VJaaspd2iU.png) Actual results: ![blender_Pmns47L7gI.png](https://archive.blender.org/developer/F14060987/blender_Pmns47L7gI.png) ![blender_jiT56z0bPb.png](https://archive.blender.org/developer/F14060989/blender_jiT56z0bPb.png) Blend file: [color attribute white noise bug.blend](https://archive.blender.org/developer/F14060955/color_attribute_white_noise_bug.blend)

Elias commented

2022-12-16 03:02:38 +01:00

Added subscriber: @razzzmatazzz30297

Germano Cavalcante commented

2022-12-16 14:41:21 +01:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-12-16 14:41:21 +01:00

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

Germano Cavalcante commented

2022-12-16 14:41:21 +01:00

I can confirm the behavior.
I'm not sure why this happens.
It is seen in both Eevee and Cycles.
And it only happens with White Noise Texture.

I can confirm the behavior. I'm not sure why this happens. It is seen in both Eevee and Cycles. And it only happens with `White Noise Texture`.

Charlie Jolly commented

2022-12-16 17:29:01 +01:00

Added subscriber: @CharlieJolly

Lukas Stockner commented

2022-12-17 01:14:18 +01:00

Added subscribers: @brecht, @LukasStockner

Lukas Stockner commented

2022-12-17 01:14:18 +01:00

This is caused by floating-point rounding differences.
The white noise node hashes its input, so the slightest change to any of its inputs will give a completely different output.

Since Vertex attributes are interpolated across the face, a calculation whose inputs depend on the shading location takes place. Of course, in exact arithmetic this should always give the same result since all vertices have the same value, but in floating-point arithmetic expressions like a*(1-b) + a*b might not always be exactly equal to a.

In this particular case, the difference in Cycles ends up being just one bit - 0x3F800000 (1.00000000...) vs. 0x3F7FFFFF (0.999999940395...). This tiny difference would never be visible for regular textures, but for white noise in particular it's enough to get a different output.
You can also demonstrate this without a white noise texture:

I don't think there's an easy fix for this, I'd lean towards just considering this a known limitation of the white noise texture.
@brecht, sounds good to you?

This is caused by floating-point rounding differences. The white noise node hashes its input, so the slightest change to any of its inputs will give a completely different output. Since Vertex attributes are interpolated across the face, a calculation whose inputs depend on the shading location takes place. Of course, in exact arithmetic this should always give the same result since all vertices have the same value, but in floating-point arithmetic expressions like `a*(1-b) + a*b` might not always be exactly equal to `a`. In this particular case, the difference in Cycles ends up being just one bit - `0x3F800000` (`1.00000000...`) vs. `0x3F7FFFFF` (`0.999999940395...`). This tiny difference would never be visible for regular textures, but for white noise in particular it's enough to get a different output. You can also demonstrate this without a white noise texture: ![Screenshot from 2022-12-17 01-06-55.png](https://archive.blender.org/developer/F14063832/Screenshot_from_2022-12-17_01-06-55.png) I don't think there's an easy fix for this, I'd lean towards just considering this a known limitation of the white noise texture. @brecht, sounds good to you?

Brecht Van Lommel commented

2022-12-17 01:25:19 +01:00

Yes, I consider that a known limitation.

Lukas Stockner commented

2022-12-17 03:37:20 +01:00

Changed status from 'Confirmed' to: 'Archived'

Lukas Stockner closed this issue

2022-12-17 03:37:20 +01:00

Lukas Stockner self-assigned this 2022-12-17 03:37:20 +01:00

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Unexpected behavior when combining Color Attributes with White Noise Texture #103255