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Transparency and reflections in Ray-traced 3D?

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Ryan HillTransparency and reflections in Ray-traced 3D?
by on Apr 23, 2013 at 7:09:08 pm

This is interesting behaviour I've discovered while playing with Ray-traced 3D. I'm hoping someone can explain why this is handled the way it is and/or a way around it if I don't want this behaviour.

Say I have
A -a layer with Reflection Intensity at 100%
B -a layer set to Appears in Reflections Only
C -a layer set to Appears in Reflections Only and transparency at 50%

And they are arranged such that I can see both B and C reflected in A with C in front of B.

Since C is transparent, you might expect to see B through C. You would be wrong. Instead, the transparency of C seems to create a transparent hole in A, precisely where C's reflection appears on A.

If you switch B to Appears in Reflections On instead of Only, then you can see B through C.




I guess it is something like the renderer doesn't treat seeing B through C in a reflection as B appearing "only in reflections" because it's also being seen through a transparency? Or something?

Now, being able to add transparent spots to the reflective object like that could have its uses, but what if I did just want the reflection of a transparent object, rather than the transparent reflection of an object?



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Walter SoykaRe: Transparency and reflections in Ray-traced 3D?
by on Apr 24, 2013 at 3:13:26 pm

[Ryan Hill] "I guess it is something like the renderer doesn't treat seeing B through C in a reflection as B appearing "only in reflections" because it's also being seen through a transparency?"

This sounds like a bug to me, and your explanation here seems like a reasonable theory as to its nature.

I'd suggest you file a bug report [link], and maybe include a link to a project file that illustrates the problem.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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