Possible bug - 2 materials on object with same medium

[FakeShamus]

Hi, I am getting some weird results when I try to use a specular and glossy transparent on one object - only the front 'lens' part of this safety goggles model. the front faces of the lens have glossy transparent with an image texture controlling the roughness (adding scratches on the surface), while I kept the side and back faces a clear specular. when I give both materials the same medium the result looks too bright. giving them separate mediums (but all the parameters the same) brightness looks correct, but the background is distorted as if the IOR is wrong, maybe multiplied. it's a little hard to describe in words, so please see the attached examples to compare. maybe I am simply setting up the materials wrong, but it seems like very different results that shouldn't be happening.

edit:
I tried one more thing, changing the specular material to glossy transparent with roughness 0, gives the correct result (not too bright and not distorted), but why the difference when using specular?

[Originalplan®]

when I give both materials the same medium the result looks too bright. giving them separate mediums (but all the parameters the same) brightness looks correct, but the background is distorted as if the IOR is wrong, maybe multiplied. it's a little hard to describe in words, so please see the attached examples to compare. maybe I am simply setting up the materials wrong, but it seems like very different results that shouldn't be happening.

If i understand it correctly....actually it should give you bright and distorted weird IOR.
Having specular and glossy transparent blend is kinda putting two very reflective surfaces together..kinda 1+1=2
So it won't end up 1+1=1. That's why the second one is correct, since the specular and glossy adds up two 2 layers of super glossy material.

You could try a blend ration between the two.
Or map the model itself so different geometry has its own material. < (aka the front and the sides)

Hope this helps.. ®

[FakeShamus]

Or map the model itself so different geometry has its own material. < (aka the front and the sides)

This is how I have it, actually, sorry if that was unclear. There's no blend...

In the end, it does make the most sense to have the materials all glossy trans, but my intuition is that it should also work with specular and GT on different faces, especially in the case where the 2 materials share 1 medium.

[thesquirell]

Maybe it has something to do with the fact that the specular materials are delta materials, while Glossy ones aren't. Not sure. My guess would be - 1) close the geometry for every medium; 2) if it's a different type of material - it's a separate geometry.

In the example below, my "frame" is one closed mesh, and the "glass" is another. All closed up, with correct precedence number (frame has the priority - it needs to "cut" into the glass). Frame-GT, Glass-Specular.