[Bf-cycles] Volume Refraction shader

[Mircea Kitsune]

Thank you for the replies and clarification. I didn't think that with a 
volume, there would be no reference point as to what the normal's 
direction is, making bending of ray trajectories difficult to calculate. 
I imagine some workaround could be found if really needed, but it could 
be more or less of a hack in that case.

Gravitational lensing would be a wonderful addition to ray calculations 
too. The main purpose for my suggestion is heat haze: As I said, there's 
currently no clean and realistic way of simulating air distortions above 
hot surfaces, which is a very problematic limitation for some projects. 
The reason I suggested volumetric refraction in particular is that the 
smoke volume of a fire simulation could be used directly to emulate heat 
refracting above a flame, making the effect very easy to embedded with 
fire / smoke simulations.