<div>Sorry the permissions were wrong on the pictures, they should work now.<div><br></div></div><div><br><div class="gmail_quote">On Thu, Nov 17, 2011 at 10:27 AM, Brecht Van Lommel <span dir="ltr"><<a href="mailto:brechtvanlommel@pandora.be">brechtvanlommel@pandora.be</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">Hi,<br>
<div class="im"><br>
On Thu, Nov 17, 2011 at 5:39 PM, Lucas <<a href="mailto:wsacul@gmail.com">wsacul@gmail.com</a>> wrote:<br>
> I'm hoping <a href="http://cgi.stackexchange.com" target="_blank">http://cgi.stackexchange.com</a> becomes public soon and has lots of<br>
> blender support for some of these possibly remedial questions:<br>
> How is volume shading done with cycles in the current svn trunk?<br>
> In the following picture the transparent shader behaves intuitively but a<br>
> glass surface shader still casts a shadow. I think this means I need to do<br>
> volume shading in addition or instead of surface shading, and in the node<br>
> editor view I see a block called 'material output' with a surface and volume<br>
> input and the surface input already hooked up, but what do I hook up to the<br>
> volume input?<br>
> <a href="https://picasaweb.google.com/103190342755104432973/Blender3D#5675708974274649330" target="_blank">https://picasaweb.google.com/103190342755104432973/Blender3D#5675708974274649330</a><br>
> Turning off shadows works for the glass objects but is only physically<br>
> correct if they are 100% white.<br>
<br>
</div>Volume rendering is not supported yet. The link doesn't seem to work,<br>
but I think this is a case where you've got caustics that path tracing<br>
can't render well. There's no simple solution to this, it requires a<br>
more advanced rendering algorithm. A workaround is to make a shader<br>
that switches to a transparent BSDF for shadow rays, using the light<br>
path node.<br></blockquote><div><br></div><div><div><br></div></div><div>I don't quite understand why the caustics doesn't work easily if the light is passing through parallel glass planes- it seems like as many paths ought to make it back from a diffuse bounce to the light source as they do in free space, unless some shortcut/'cheating' is helping out with the free space path, or the probabilistic path termination is really aggressive after a single free space to glass transition. Can I get correct results (like the light source passing through the glass ball in <a href="http://www.cs.berkeley.edu/~sequin/CS184/TOPICS/GlobalIllumination/Gill_0.html">http://www.cs.berkeley.edu/~sequin/CS184/TOPICS/GlobalIllumination/Gill_0.html</a> and projecting and interesting light pattern on the wall and floor) if I crank up the render cycles (going to try it myself but it may take a while).</div>
<div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im"><br>
> Is there any way to pass hints to send more lightpaths bouncing off one<br>
> object to a secondary object?<br>
> In this example there are light paths that hit the diffuse bsdf of the<br>
> shadowed area of the plane and only a few of them hit the mirror and trace<br>
> back to the light source I have pointed at the mirror, resulting in only a<br>
> smattering of light reflected by the mirror. Many many more render cycles<br>
> would fill in the gaps but at huge cost.<br>
> <a href="https://picasaweb.google.com/103190342755104432973/Blender3D#5675634439005970706" target="_blank">https://picasaweb.google.com/103190342755104432973/Blender3D#5675634439005970706</a><br>
><br>
> One approach that comes to mind is to have a special shader that takes an<br>
> object as a target, so that the peak response is always pointed towards it<br>
> (but also has a softness factor that maybe would have to be increased<br>
> manually if the target object is large and close, or there could be an<br>
> automatic way of doing that). Is that possible already?<br>
> My workaround is to use a mirror modifier, and I think some additional<br>
> compositing work could make it so light from that mirrored light source that<br>
> doesn't strike the profile of the mirror is masked out.<br>
<br>
</div>Again the link doesn't work, but this seems another case that path<br>
tracing can't handle well. Caustics need a more advanced algorithm<br>
like bidirectional path tracing or photon mapping.<br>
<br>
Brecht.<br>
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</blockquote></div><br></div><div><br></div><div>Thanks, that is very helpful.</div><div><br></div><div>Lucas</div>