Alpha Channel of Base Color in PBSDF Shader shows strange behavior #67327

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opened 2019-07-20 16:14:09 +02:00 by Gaia Clary · 7 comments
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Broken: master

Short description of error

Setting an Alpha value for the Base Color of the PBSDF Shader results in strange behavior in eevee and is fully ignored in Cycles

Exact steps for others to reproduce the error

  • Open this blendfile: color_with_alpha_issue.blend
  • The front left plane has base color with alpha=0.5 and Shader Alpha Value=1.0
  • The front right plane has base color with alpha=1.0 and Shader Alpha Value = 0.5

I would expect that both planes show similar behavior, but it appears to me as if:

  • in Cycles the Base color alpha is completely ignored in the viewport
  • in eevee the Base color alpha results in strange effects in the viewport
  • rendering with eevee and cycles both fully ignore the base color alpha channel

Also it seems like once you have added alpha to the Base color, the object continues to look strange even when you set the Base node alpha back to 1.0. You can see the strange viewport display best with the 2 cubes in the back. It appears to me like there is a normals issue. But the normals seem OK.

**Blender Version** Broken: master **Short description of error** Setting an Alpha value for the Base Color of the PBSDF Shader results in strange behavior in eevee and is fully ignored in Cycles **Exact steps for others to reproduce the error** - Open this blendfile: [color_with_alpha_issue.blend](https://archive.blender.org/developer/F7620298/color_with_alpha_issue.blend) - The front left plane has base color with alpha=0.5 and Shader Alpha Value=1.0 - The front right plane has base color with alpha=1.0 and Shader Alpha Value = 0.5 I would expect that both planes show similar behavior, but it appears to me as if: - in Cycles the Base color alpha is completely ignored in the viewport - in eevee the Base color alpha results in strange effects in the viewport - rendering with eevee and cycles both fully ignore the base color alpha channel Also it seems like once you have added alpha to the Base color, the object continues to look strange even when you set the Base node alpha back to 1.0. You can see the strange viewport display best with the 2 cubes in the back. It appears to me like there is a normals issue. But the normals seem OK.
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Added subscriber: @GaiaClary

Added subscriber: @GaiaClary
Brecht Van Lommel was assigned by Gaia Clary 2019-07-20 16:18:01 +02:00
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Added subscriber: @brecht

Added subscriber: @brecht
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Hi, @brecht This issue may be is related to https://developer.blender.org/T62794 ?

Hi, @brecht This issue may be is related to https://developer.blender.org/T62794 ?

Added subscriber: @christian

Added subscriber: @christian

There is an additional issue around that I think: alpha blend mode make transparency even if alpha value is 1 (Alpha entry, not the one of BaseColor). But it seems to respond correctly to an alpha < 1.

So changing alpha on BaseColor only 'seems' to have an effect due to that.

There is an additional issue around that I think: alpha blend mode make transparency even if alpha value is 1 (Alpha entry, not the one of BaseColor). But it seems to respond correctly to an alpha < 1. So changing alpha on BaseColor only 'seems' to have an effect due to that.

Additionally, the tooltip on 'alpha blend' says: "render polygon transparent depending on alpha channel of the texture"... so do we expect the alpha of BaseColor to work (it is not apparently) of the one from the Alpha input?

Additionally, the tooltip on 'alpha blend' says: "render polygon transparent depending on alpha channel of the texture"... so do we expect the alpha of BaseColor to work (it is not apparently) of the one from the Alpha input?

Closed as duplicate of #62794

Closed as duplicate of #62794
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Reference: blender/blender#67327
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