How are Photons distributed with PhotonGI cache?
I made some obervations which make be think there is potential for optimization of the PhotonGI cache.
First, the reference picture CPU BiDir, 250 Samples
![Caustic Pacman CPU BiDir large_model_s.png (4.76 MiB) Viewed 5072 times Caustic Pacman CPU BiDir](./download/file.php?id=4257&t=1&sid=b8c10fc7de904fb17e6772488fdc6b93)
- Caustic Pacman CPU BiDir
Second, the openCL version with PhotonGI cache.
![Caustic Pacman GPU Path large_model.png (3.74 MiB) Viewed 5072 times Caustic Pacman GPU Path, openCL](./download/file.php?id=4258&t=1&sid=b8c10fc7de904fb17e6772488fdc6b93)
- Caustic Pacman GPU Path, openCL
Obviously, there are differences. I could reduce Look up radius for Caustics, This would lead to smaller or invisible spots.
I tried changing different parameters ending with more or less the same result. Largest influence here is Look up radius for Caustics. The other add time for the initial phase, in best cases to a bit denser distributed spots.
These observations lead be to the question at the start of this post: How are Photons distributed with PhotonGI cache?
Probably the PhotonGI cache and its radius behave like showed on the left side in the picture below.
![PGIC.png (276.57 KiB) Viewed 5072 times How are Photons distributed?](./download/file.php?id=4259&t=1&sid=b8c10fc7de904fb17e6772488fdc6b93)
- How are Photons distributed?
I'd like to suggest PhotonGI cache should follow the pattern of the right side of the picture above. The reason for the growing radius is it warrants overlapping of the caching space.
A solution could be to introduce one or two factors. Default would be values for an constant radius. And advanced would change the radius with distance to emission source. Advanced would enable to change one or two factors meaning (a) r_n+1=factor_1*r_n or (b) r_n+1=factor_1*(r_n)^2+factor_2*r_n.
EDIT: But maybe the cache rather looks like the following picture.
![PGIC_2.png (32.17 KiB) Viewed 5054 times How are Photons distributed?](./download/file.php?id=4260&t=1&sid=b8c10fc7de904fb17e6772488fdc6b93)
- How are Photons distributed?