I have made a scene which looks quite nice. It is a Japanese water garden with some nice fog. Unfortunately, Cycles only renders fog on cpu. If I were to render the entire scene on cpu it would take hours, even with 8 cores. I have an RX 480 that I would like to render everything but the fog with, and then render the fog with cpu and somehow composite them together. I cannot figure out how this is done. Any help is appreciated. Thanks in advance!
EDIT: I do not have the environmental fog turned on. I have a cube with some voronoi and cloud displacements and then a volume scatter shader.
My current solution if anyone has a similar issue (Works for environment textures not showing too) is to render my scene in chunks (Ground, trees,etc.) using render layers and saving them individually. I switch to cpu to render the fog, and go to an empty layer with transparency disabled for the environment, and then layering them using Gimp.
You could also use a linked scene in the blend file, but with different render settings, and then render only the volume in the CPU scene, and everything but in the GPU scene. Also, I think that heterogenous volume scatter is an experimental GPU feature (correct me if I’m wrong).