Re: ambient lightsource

["Thomas Helzle" <thomashelzle(at)gmail.com>]

Hi Pingo,

I had to write such a "distance shader" once and also was surprised that nothing like that exists in MR (or does it?). While you can build it in the tree as guillaume showed, that isn't exactly fun anymore after the third time, is it ;-)   
I needed it to modulate the thickness of ink lines getting thicker by distance from a certain point in an illustration, so I built in an object picker (can be anything, not just lights) and different ways to evaluate the distance from it (spherical, circular, linear) and some bias and gain stuff to get a nice, slightly curved inkline.
Maybe I should dig it out again...?

Basically you could just add something like that on top of each shadertree in your scene. 

I just tried what happens if you add it with a mixer to a light-shadertree, since that would make it much easier to control and setup:
It works (cool!), but only over 90°  :-(  since Mental Ray still thinks that it is a cool idea to just evaluate light on one hemisphere for optimization reasons for all the built in shaders. When I use a material that evaluates 180° it works just fine, only the shadows are bad since I never had the time or pressing need to build in a workaround for the splotchyness that occurs since MR never has that problem and therefore doesn't handle it properly (explanation see here: 
http://www.blender.org/development/release-logs/blender-234/misc-improvements/  Blender solved it quite some time ago ;-) )

You can only disable that MR "90° optimization" in a material, not in a light shader if I remember correctly. Too bad, otherwise a simple ambient-lightshader could be written...

It would also be easy if scene ambience would be connected to a shadertree or if global shaders would exist that could be connected to multiple objects/trees at once.

Cinema always had some nice things like that - especially their cheap, superfast fake volumetric lights were extremely useful back in the days of a Pentium 90 :-), I also liked point lights with shadow maps and some other ideas. But at the end of the day, XSI still beats C4D for me.

Cheers,

Thomas Helzle