I'm playing round with a fairly common Cycles node setup for glass that gives the reflections of glass but without the darkness that you get with the default glass shader:
The left panel uses a custom 'fast glass' material (node setup below), and the right one uses just the default glass shader. While I'm expecting the double reflections on the left panel - since that's what happens with glass IRL - they seem really far apart depth wise. The glass is only 12mm thick, so I was expecting those two reflections to be almost on top of each other. Also, one of the reflections is noticeably larger than the other, which I imagine is also due to the exaggeration of depth. I'm stumped as to why.
- Both glass panels have had scale applied.
- Both glass panels are closed meshes at 12mm thick.
- Both glass panels are flat shaded, with normals facing outwards.
- The default glass is using the default glass shader with an IOR of 1.450 degrees.
- The 'fast glass' uses the following material:
File uploaded here (swapped out the floor so I could drop the texture, but otherwise the nothing else changed):
Tinkering some more, I noticed that if I use the Shadow Ray and Diffuse Ray as my factor I get just the one reflection, so it looks very similar to the standard glass shader, minus the shadow. Interestingly if I use the glossy ray I get a lot of refraction going on, which doesn't seem right given the thickness of the material, but I can't begin to figure out why.