Texture properties not working with OSL enabled and unpacked textures #86764

New Issue

b5327157 · 2021-03-20T13:18:27+01:00

b5327157 commented

2021-03-20 13:18:27 +01:00

System Information
Operating system: Linux-5.11.7-arch1-1-x86_64-with-glibc2.33 64 Bits
Graphics card: Mesa DRI Intel(R) HD Graphics 520 (SKL GT2) Intel Open Source Technology Center 4.6 (Core Profile) Mesa 20.3.4

Blender Version
Broken: version: 2.92.0, branch: master, commit date: 2021-02-24 16:25, hash: 02948a2cab
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-03-19 21:37, hash: 3494946560

Short description of error
I have a texture with RGB channels set to 1 and alpha set to 0. When trying to use this texture with OSL, the alpha property (at least) of the image texture node does not work when the texture is unpacked. I set it to channel packed, expecting the color data to be always white. The problem is that when the texture is unpacked, the color data is black.

Exact steps for others to reproduce the error

Open the attached file.
Set viewport shading to rendered.
The plane shows as white (as it should).
Unpack the texture.tga file.
Toggle between preview and rendered viewport shading to refresh.
The plane now shows as black.
Pack the texture again.
The plane shows as white again.

bug.blend

**System Information** Operating system: Linux-5.11.7-arch1-1-x86_64-with-glibc2.33 64 Bits Graphics card: Mesa DRI Intel(R) HD Graphics 520 (SKL GT2) Intel Open Source Technology Center 4.6 (Core Profile) Mesa 20.3.4 **Blender Version** Broken: version: 2.92.0, branch: master, commit date: 2021-02-24 16:25, hash: `02948a2cab` Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-03-19 21:37, hash: `3494946560` **Short description of error** I have a texture with RGB channels set to 1 and alpha set to 0. When trying to use this texture with OSL, the alpha property (at least) of the image texture node does not work when the texture is unpacked. I set it to channel packed, expecting the color data to be always white. The problem is that when the texture is unpacked, the color data is black. **Exact steps for others to reproduce the error** 1. Open the attached file. 2. Set viewport shading to rendered. 3. The plane shows as white (as it should). 4. Unpack the texture.tga file. 5. Toggle between preview and rendered viewport shading to refresh. 6. The plane now shows as black. 7. Pack the texture again. 8. The plane shows as white again. [bug.blend](https://archive.blender.org/developer/F9900836/bug.blend)

b5327157 commented

2021-03-20 13:18:27 +01:00

Added subscriber: @b5327157

Germano Cavalcante commented

2021-03-23 20:25:01 +01:00

Added subscribers: @Jeroen-Bakker, @mano-wii

Germano Cavalcante commented

2021-03-23 20:25:01 +01:00

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

Germano Cavalcante commented

2021-03-23 20:25:01 +01:00

Thanks for the report, I can confirm.
This seems to be related to the pre-multiplication of alpha.
Although this is partly by design, this inconsistency should not exist.

The image editor is also pre-multiplying the alpha even when you just want to see the colors.
This didn't happen before, (maybe it can be considered a regression?)
@Jeroen-Bakker, on this second issue, I don't know if it's related to the changes to the image editor's drawing, but maybe you know what's going on?

Thanks for the report, I can confirm. This seems to be related to the pre-multiplication of alpha. Although this is partly by design, this inconsistency should not exist. --- The image editor is also pre-multiplying the alpha even when you just want to see the colors. This didn't happen before, (maybe it can be considered a regression?) @Jeroen-Bakker, on this second issue, I don't know if it's related to the changes to the image editor's drawing, but maybe you know what's going on?

b5327157 commented

2021-03-27 16:26:20 +01:00

The more general question to ask is that why is the OSL texture function doing alpha pre-multiplication in the first place? In such case it will not be possible to recover information from RGB channels when alpha is zero. I am not aware of any requirement regarding pre-multiplied alpha in the OSL specification.

Philipp Oeser removed the

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Texture properties not working with OSL enabled and unpacked textures #86764