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Cycles Bake Selected to Active with transparency gives undesirable results
Open, Needs Triage by DeveloperPublic

Description

System Information:
Operating system: Windows-8.1-6.3.9600 64 Bits
Graphics card: GeForce GT 635M/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 391.35
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-20 14:27, hash: rB26bd5ebd42e3

Bug or unintended behavior:
Baking using "Selected to Active" does not take into account transparency

How to reproduce:
Create two objects with materials and textures assigned to each;

One texture to be baked to
One texture with an alpha channel (optionally a normal map)

In the shader editor, modify the material of the object with a transparency channel

Join the transparent textures' alpha into the alpha of the shader that is being used
(optionally join the color of a normal map)

In render properties, enable Selected to Active and use an appropriate ray distance

Finally bake.

Result:
When baking combined or most channels, the transparent areas will assume the color as if it were completely opaque,
When baking normals with transparency, the transparent areas will mix with the normal of the geometry that is being baked to the active selection.
Both outcomes are unfavorable when working with transparent cards/ribbons.

Details

Type
Bug

Event Timeline

Is this similar to T50698?

Issue referenced appears to be about color mixing

The project referenced can be slightly modified and shows the problem still exists pre-2.80

Left is the diffuse bake with overlapping quads drawing completely opaque overtop of each other, right is the render viewport, which is what I would have expected the bake to do.