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roberthurt
03-05-2010, 07:30 PM
I've run into what appears to be a buggy interaction between transparency and refraction in a relatively simple scene.

I have modeled a simple conical lens that flares out to a flat surface at the edges that qualitatively simulates the light distortion around a black hole. However when I place it in front of a disk that has a transparency gradient out to the edges, it seems like the transparency of the disk changes significantly where it intersects the "lens". If I turn off the disk's transparency then the lens renders the distortion and the disk correctly.

The problem also goes away if the "lens" has an extremely low refractive index (1.02 or lower). However while trying different settings I found an intermediate value that created a partial artifact (refractive index = 1.03).

I've included the three cases as attachments. No disk transparency, disk transparency with the refraction artifact, and a small refractive index with a partial artifact.

Does anyone have insights into this?

dandeentremont
03-06-2010, 10:11 AM
Sometimes upping ray recursion limit to 16 (if it is not that already) can fix certain transparency issues. Also try messing with ray trace occlusion/ transparency.

toby
03-06-2010, 03:40 PM
Also makes sure you don't end up with any negative transparency.

If that and upping the recursion doesn't do it, we'd need to know more about your scene to diagnose it - where the geometry lies, what's double-sided and what's not, it's surface/object properties, render settings, etc. It's even better if you can post the scene & objects.