Shader Question

[anm8sanjose]

Hello all,
got a question about shaders and shadows. I use both XSI and maya. in Maya there is a shader called background that you can use to add shadows to movie clips and photographs. the way it works is that you take your shape and apply the background shader to it. what this does is applies a portion of the background to the shape so that the shape will accept shadows but will blend into the video clip or photo. How can one do this in XSI? any help would be great as i hate having to toggle between the two for these effects.

thnx,

chant

[dickagm]

Realy I never render the final composition in Maya or XSI, I'm separating it to passes.. (all things, like color, difuse.. etc) are the first pass and shadows are separated in second pass (in most situations 2 passes are enough). By this way you can adjust super faster the shadow blending, bluring and even a color.
I'm not so familiar with XSI, but I think that you can do this with rendering passes in XSI. There you can choose "Shadow Pass" to render it and in compositing software to add the shadows only.

[bishamon]

I'm also new to XSI but I've managed to find an answer to your question..
if you are asking about the "use Background" shader in maya...
There is a shader called "Shadow" in XSI (found under nodes>Illumination)
Connect that to the material surface port in the render tree
you'll get the object to render where it recevies a shadows only and it also affects the alpha of the image (i.e exactly the same result as the use background shader in maya)
there's 1 artifact I've found and I don't know the reason for it.
You'll get a variiation in the shadow color in form of long horizontal stripes
to solve that you'll find a min/max values in the "shadow" shader
set them both to the same value
I'd recomend setting them both to zero if you plan to render the shadow on a seperate pass and the fine tune the shadow color in the composoting stage.

if you prefer to have the object and it's shadow on the same pass just set the min/max values to anything else than 0 or 1