Re: ambient lightsource

["Matt Lind" <speye_21(at)hotmail.com>]

After thinking a bit, I remembered to look in the "duh" file.

You can compute the ambient effect using existing nodes in the rendertree. 
The setup is as follows:

1) Activate incandescence on your material shader with desired color.  The 
associated intensity parameter will drive the effect.

2) Get a vector share shader.  Apply an expression to the input parameter so 
it's driven by the global position of an object in the scene - doesn't have 
to be a light.

3) Get a vector_state shader.  Set the operation to "intersection point". 
This is the coordinate of the point on the surface currently being rendered.

4) Get a vector-scalar node from the Math shaders.  Connect the two vector 
shaders to the inputs of the vector-scalar shader.  Set operation to 
"distance between v2 and v1".

5) Connect output of vector-scalar shader to input of a change_range shader. 
Set the old start and end parameters to your min/max range for the ambient 
effect.  So, if old range start / end are 3 and 10 respectively, then any 
shading point within 3 units of the designated ambient light object will 
receive 100% incandescence.  Any shading point more than 10 units away will 
not receive any incandescence at all.  Anything inbetween will receive 
incandescence at reduced intensity with linear falloff.  Set the new range 
start to 1 and new range end to 0 because we want to inverse the falloff and 
keep the result within a legal range.

6) Connect the output of the change_range to the incandescence intensity 
parameter on your material shader.

7) Preview the effect in the render region.  voila!

Since the computations are mostly to determine intensity, you can apply this 
as an override to all objects in the scene while each can have it's own 
incandescence color.  They'll just share the same intensity.


Matt

--------------------------
Matt Lind
Animator / Technical Director
Softimage certified instructor:
   Softimage|3D
   Softimage|XSI
Matt.Lind(at)Mantom.net


Date : Sat, 1 Dec 2007 10:43:30 +0100
To : XSI(at)Softimage.COM