Operating system: Linux-4.13.10-041310-generic-x86_64-with-debian-stretch-sid 64 Bits
Graphics card: GeForce GTX 1050/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 390.67
Broken: version: 2.80 (sub 70), branch: master, commit date: 2019-05-20 06:52, hash: rBf606f588455e
Short description of error
This is a follow up to T64762, so I think @Brecht Van Lommel (brecht) might want to take a look at this.
The problem is a bit hard to pin point, but there still seem to be a problem with linear interpolation of alpha mapped normal maps. This time they are only triggered when a value node, specifically with a value of 0, is used as the input for either Subsurface, Clearcoat or Transmission on the Principled PBR node.
When the value node is muted, or the connections are cut, the issue is gone. That is despite the fact, that the values on the Principled node are the same, as the value coming from the input node.
There is another, perhaps related, darkening issue. If instead of using the transparent shader to mask the object, the alpha inputof the Principled PBR node is use, the entere material darkens.
This again is triggered by the Subsurface, Clearcoat or Transmission inputs, and vanishes when the value node is muted or the connections are cut.
I also think this only happens for non-metallic materials, but I'm not sure.
Please check out the video demo for clarity.
Exact steps for others to reproduce the error
- open the blend file above
- notice - what appears like - interpolation issues on the transparent border
- mute or disconnect the value node, feeding a value of 0 to subsurface, clearcoat and transmission
- the issue should be gone, but note that the input values are the same as before
- unmute/reconnect the value node
- feed the Principled output directly Material Output, to use the shaders own alpha input in favor of the Transparent and Mix shaders
- now the entire material should darken
- mute or disconnect value node again, and the material will behave as expected