There is no such thing as a physically accurate render engine. You’d probably get closer setting up Mitsuba if you had the know how, but don’t expect quick results. It’s all about simulation, approximations, and simplifications to get render times we can live with. When we talk about physical rendering, accuracy is actually pretty far behind. We’re talking about reduced data sets to drive it, and plausability in the result. If using plausible albedo values on Principled, I haven’t heard anyone complaning about it not being accurate enough. If you’re turning off caustics as a means to do light transport for noise reasons (I usually do), it already breaks the argument of accuracy.
Disney has already improved their shader to support thin and translucency effects in their shader. We’re just lagging behind a bit. And even if they have, it still doesn’t support all the other shader types they have. It’s a shader that does 90% of the jobs, and does it more than adequately. In our case, it just doesn’t do translucency (or velvety) effects.
No. But it is still more physically plausible than what you would get from manual setup if you didn’t know what you were doing. In fact, you can’t even get the plausability from Principled using the building blocks, because Diffuse roughness simulates Oren-Nayar whereas Disney roughness simulates Disney diffuse which takes into account diffuse exit IOR.
Technically speaking, I would say Moony’s approach here is wrong, since glossy is already covered in the glass shader thus done twice.
Artistically speaking, if it looks good, then use it. Don’t be too strung up about it being physically “accurate”.
Fairly speaking, what’s wrong with ajm’s approach of just basing it on rough refraction?
I’ve done this for 20+ years, and maybe I’ve developed a bit of unfortunate purism. No need for you to do so. I presented my method of thinking about pretty much any general surface shading setup. I showed how to deal with translucency. Do you even need it? Did you measure the samples backlit diffuse shadow qualities? Also, keep in mind that “doing it the right way” theoretically may not produce the results you want. Cheating is ok.