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

Lucas wsacul at gmail.com
Fri Nov 18 01:48:56 CET 2011

On Thu, Nov 17, 2011 at 11:42 AM, Brecht Van Lommel <
brechtvanlommel at pandora.be> wrote:

> Hi,
> On Thu, Nov 17, 2011 at 8:05 PM, Lucas <wsacul at gmail.com> wrote:
> > 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
> http://www.cs.berkeley.edu/~sequin/CS184/TOPICS/GlobalIllumination/Gill_0.html
>  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).
> If Glass IOR is exactly 1, it could indeed do the same as it does for
> the Transparent. For other values, this requires a different
> algorithm. I think it's good to keep different sampling behavior for
> different nodes, suddenly doing something when IOR is 1 is not really
> predictable, and it would give strange results when texturing this
> input.

No I wouldn't want special case code either.

> I guess you can get the results from that scene, if the light source
> is a mesh with an emission shader, it's just going to take a long time
> for the noise to clean up.
> Brecht.

I did more rendering and now I can see the transparency is working as it
ought to, I just didn't know it would take so many cycles to get this far:


Now I think I'll have to resort to more tricks to simulate this in less
renders, maybe by setting a camera to capture light coming through a
transparent object from a certain point of view and then re-emitting that
light from the back of the camera.  For that and other purposes it would be
really useful to have a non-lambertian emission shader, so I could send
light rays from a texture only in narrow lobes along the surface normal and
use it as a projector (maybe have a 0 - 1.0 slider to scale inbetween pure
lambertian and pure normal).  If that doesn't exist maybe that's a good
excuse to learn how to make it myself.


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