Object with primary rays off still renders the truth about transparency secondary rays
Article needs peer review
Symptom
A scene contains two objects: a grid has a texture with an alpha channel transparency mask (cutout trick), and a cube that is placed behind the grid. The scene in this example, is setup for Final Gathering rendering. The cube is acting as a FG light source, and should not be seen in the final render. So, the cube’s Primary rays (and shadows) are turned off, leaving the Secondary rays enabled.
The rendered result shows the cube visible in the scene, as if its Primary rays were turned on, when in fact the cube should not have been visible at all?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
Cause
This behavior is by design. Transparency rays are considered Secondary rays. As a result, if Transparency rays hit an object that has its Secondary rays enabled, then it will be rendered, although the object’s Primary rays are turned off. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
Solution
The workaround solution is a simple one:
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Open the Render tree for the background object, in this case, the cube with the Secondary rays enabled.<o:p></o:p>
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Connect a Ray_type shader (from: Render tree>Node>Switch) between the material surface and what was connected to material surface.
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The tree needs to be connected to Ray_type-Eye parameter only; Refraction should be left unconnected, and set to values of 0,0,0,0. </DIV></OL></SPAN>
References
Applies To: XSI 2.0,XSI 2.0.1 on NT,Win2K,Irix
Posted: 1/10/2002
