[Bf-cycles] Volume shaders, mirrors that project light sources

Lucas wsacul at gmail.com
Thu Nov 17 17:39:25 CET 2011

I'm hoping http://cgi.stackexchange.com becomes public soon and has lots of
blender support for some of these possibly remedial questions:

How is volume shading done with cycles in the current svn trunk?

In the following picture the transparent shader behaves intuitively but a
glass surface shader still casts a shadow.  I think this means I need to do
volume shading in addition or instead of surface shading, and in the node
editor view I see a block called 'material output' with a surface and
volume input and the surface input already hooked up, but what do I hook up
to the volume input?


Turning off shadows works for the glass objects but is only physically
correct if they are 100% white.

Is there any way to pass hints to send more lightpaths bouncing off one
object to a secondary object?

In this example there are light paths that hit the diffuse bsdf of the
shadowed area of the plane and only a few of them hit the mirror and trace
back to the light source I have pointed at the mirror, resulting in only a
smattering of light reflected by the mirror.  Many many more render cycles
would fill in the gaps but at huge cost.


One approach that comes to mind is to have a special shader that takes an
object as a target, so that the peak response is always pointed towards it
(but also has a softness factor that maybe would have to be increased
manually if the target object is large and close, or there could be an
automatic way of doing that).  Is that possible already?

My workaround is to use a mirror modifier, and I think some additional
compositing work could make it so light from that mirrored light source
that doesn't strike the profile of the mirror is masked out.

Thank you,

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