Let's not over-complicate things here.
The Redshift material can look intimidating, but that's because it has Multiple Scattering SSS, Clear Coat, Optimizations, Advanced tabs and about 1 gazillion map inputs. These have nothing to do with what we are interested in (Right now).
Let's only look at the Diffuse/Reflection part, and see how elegantly Redshift has merged old-school IOR and PBR. Nothing needs to break in CoronaMtl. (Refraction has the same settings as Reflection, no need to include that here).
Look how similar the materials are.
That's only two new drop downs, people who don't give a shit about PBR can just leave those two drop downs alone and all the old materials will work as they did before.
"Weight" is the same as "Level" in Corona, only with map support, so don't get confused by that.
Let's have a look at the PBR portion of Redshift.
So what has happened here? We changed "Fresnel" to "Metalness".
- This disabled "Weight" aka "Level".
- "IOR" got changed to "Reflectivity" and "Metalness".
The default "Reflectivity" value is 4% the same as IOR 1.5, same result.
When "Metalness" is at 1, the specular color is sampled from "Diffuse Color".
As you can see, it's not that complicated to have both worlds in one material. Nothing will break for existing materials. People who don't care about PBR, can just leave that "Fresnel" drop down alone.
Welcome to Corona 1.5 where everyone is pleased!
EDIT:
I forgot to mention that Redshift is handling the Roughness/Glossiness issue pretty nicely too.
Roughness is default, which is the most logical solution if you ask me.
But inside the material you have this option
It will invert both values and maps, very clean and nice solution.
Corona could do something like, the first time you open a legacy scene, this checkbox is on. So the material will read everything as Glossiness.
But for new materials the check box is off, roughness as default.
All the problems are solved.
