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Backfacing transparency appears black in GPU (OpenCL) rendering - Cycles
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Description

System Information
System 1:
CPU: Ryzen 5 2600
GPU: RX 570 4GB
OS: Windows 10 Home

System 2:
CPU: Ryzen 5 2500U
GPU: Vega 8
OS: Windows 10 Home

Blender Version
Broken:
Blender 2.79b
Blender 2.79 Master d7f55c4ff58 (November 15)
Blender 2.8 c94f806dc73 (November 15)

Short description of error
If an object material has the "Backfacing" output of the "Geometry" node plugged into a mix node in a way that the back face is transparent, that back face will appear black in the final render on the GPU (only tested with OpenCL). Viewport rendering is unaffected.

Here's an example of what I mean:

Node tree:

CPU Render/Expected result:

GPU Render:

Exact steps for others to reproduce the error
Here's a few Blend files to test with:

2.79b and Master:


2.8:

Details

Type
Bug

Event Timeline

Cannot reproduce (but am on linux with 970m).
Which driver version is this? (Have you tried other driver versions?)

The Vega 8 GPU is running driver version 17.7
The RX 570 is running diver version 18.10.2

I'm unable to try different drivers on the Vega 8 due to how AMD has setup it's distribution, but I'll give the RX 570 a try on different drivers once my current render is finished.

I have the same problem
ubuntu 18.04
amd pro driver 18.50
amd Fx 8150 + RX 580
when I use "life render" on GPU it works fine
when press f12 it goes black both sides (I use plane, not cube)

edit
I've installed win 10 on the same computer with newest amd gpu driver and results are the same :/