Weird glass material shading in Cycles (bug)?

Can anyone shed some light onto this?


Is anyone supposed to be able to read that ?

Rather than faff around trying to decipher it, strip out all the unnecessary bits of the scene and just post the basic blend file that still gives the same result.

Its a simple glass shader with three versions.

Top one is using Glass node. Middle one is using a Refraction/Glossy blend using Layer weight with 0.3 fresnel.
Bottom one is same as middle but using fresnel of 0.5.

It seems that the problem starts if Layer weight >=0.5. Bounces don’t make a difference same as samples. Also why is refraction shader blocking shadow rays, I must be doing something wrong here.

Attached is a simplified scene.

test.blend (960 KB)

I see your window panes have thickness. Don’t get me wrong: That’s essential and correct if you use any kind of refractive material (glass/refraction shaders), but it is also costly concerning render times and prone to end in fireflies because of the caustics.

With “architectural glass” (windows etc., that have a negligible refractive effect anyway) I therefore tend to skip refractive materials completely and just go with flat glass planes and a glossy/transparent mix (as I linked to in my last post). That will converge a bit quicker and is less of a hassle to set up.