[Bf-cycles] Volume Refraction shader

[Zauber Paracelsus]

I had suggested this a while back, though with a different purpose in 
mind, which was to produce a gravitational lensing effect.

On 02/05/2017 05:45 PM, Mircea Kitsune wrote:
> This is something I've been wanting to get to the developers to for a
> while. It's a feature I hoped to use on several occasions, but
> unfortunately it doesn't exist nor seems to be in any official plans as
> of yet. Please consider a solution if possible. Thank you.
>
> Suggestion request: Implementing a volume refraction shader. Either by
> allowing the existing Refraction BSDF to work on the Volume material
> output, or by defining a new Volume Refraction shader if that is a
> better approach.
>
> Suggested functionality: When a ray passes through a volume affected by
> this shader, its trajectory is bent, just like Glass BSDF or Refraction
> BSDF does for surfaces. Optionally, an IOR value may let users define
> the probability and / or angle at which rays have their course modified,
> whereas a Roughness value adjusts how blurry the view gets through such
> a volume... the two ideally operate in an independent way so that
> refraction and blur can work without one another.
>
> Purpose 1: The most important practical use of this shader is proper
> heat haze, emulating the air deformations we see above hot ovens / jet
> engines / roads during summer days. As a workaround, this is already
> possible to do with render nodes, by rendering your volume as a black &
> white mask on a different render pass then plugging it into the Vector
> input of a Displace node through which the main render is passed.
> However this is just a workaround that so happens to work: It leads to
> quality loss due to smudging and stretching the render result, causes
> empty spaces if the transformation of the mask warps near an edge, is
> much less realistic compared to the ray actually traveling a different
> trajectory, and might ultimately be slower depending on what
> calculations are implied.
>
> Purpose 2: This would allow a greater level of detail for objects such
> as crystals, diamonds, gems, ice crystals, and other types of rough
> glass. You can already design realistic crystals in Cycles, by
> customizing the IOR and Roughness of a Glass BSDF or Refraction BSDF,
> causing different spots to refract or blur in different amounts. However
> you can't differentiate such spots volumetrically inside the crystal
> itself, and can't create rough blurry strands or inner glass pieces that
> have a different refraction angle from others. This can of course be
> worked around by adding smaller meshes inside the main crystal and
> giving them different materials, but this technique will cause sharp
> edges and is less correct and flexible compared to volumes in many cases.
>
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