ISO clarification re: outTransparency 2003-12-08 - By Mike Mcaulay
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There's something about the outTransparency attribute of shaders that I
don't understand. It appears that it affects the transparency of target
meshes even though it is not explicitly connected to an attribute on the
shadingGroup. For example, if I apply the default lambert1 shader to a
piece of test geometry and drag the Transparency slider back and forth, the
geometry's transparency is affected. But if I go into the Hypershade window
the only connection I see is lambert1.outColor ->
initialShadingGroup.surfaceShader. And if I look in the Connection Editor I
see that the OutTransparency attribute is not in fact connected to any
attribute on the shading group (indeed, there does not appear to be a
reasonable candidate attribute to which it could be connected).
The docs for the ShadingEngine node (aka shading group) state that "the
renderer will evaluate the "outColor" and "outTransparency" attributes of
the shader attached to the surface shader port to determine the color and
transparency of the objects, respectively." So, I guess that means that
outTransparency is somehow "magical," and takes effect even when it is not
connected.
My questions are: 1) Am I understanding this correctly? 2) Where does the
magic reside? Does the shading group node traverse upstream to the shader
and query its outTranparency attribute, or does some piece of internal Maya
code do it?. And finally, 3) what other attributes are similarly magical?
I am fairly new to Maya coding, and I was just getting comfortable with the
notion that I could rely on Maya's tools (hypergraph, hypershader, etc.) to
tell me what was going on. But now it seems that - in at least one case -
there is some extra voodoo that has to be accounted for.
Thanks in advance to anyone who can shed light on this subject.
Mike
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