AcademySoftwareFoundation
Remove provision for specular_weight to exceed 1
As discussed on Slack, the spec is currently inconsistent about the range of specular_weight.
For dielectrics, we allow it to exceed 1, as a sort of convenience. For metals, we don't (or at least didn't intend to, as it breaks energy conservation), but this doesn't make sense since there is only one parameter with a defined range.
This PR makes the specular_weight consistently bounded in $[0,1]$. As noted by @peterkutz
I noticed this inconsistency while implementing this specular scaling a few days ago. I wasn't sure whether it was intentional but I implemented it following the ranges in the spec, so the specular weight is uncapped for dielectrics and capped at 1 for metals.
I agree that it would be cleaner to just remove the ability to set the specular weight higher than 1. If the specular weight is being set using a 0–1 texture, it won't go higher than 1 anyway, and if it's being set via a constant or an HDR texture, then the IOR or metal colors could just be set directly.
This also simplifies the implementations slightly.
Since this is a potentially look breaking change without a way to restore the previous look, we need to discuss which branch/version this change would target before considering merging. It is also arguably a loss in functionality so I would like to see if there is a consensus.
Corresponding change to MaterialX graph to follow..
Done in aee8093ef98a05d6bfa0658e9108d8cdf8414004 (just removes a clamp).
If we decide to go with the proposal of https://github.com/AcademySoftwareFoundation/OpenPBR/pull/238, we can delete this PR.