01 January 2004, 11:41 AM
Originally posted by faceForward
I'm new to PrMan and i have a question regarding displacing a surface that has hair geometry atteched to it.
the geometry for the offscreen-originated strands is not displaced since it's not in the currently active bucket, how do the hair strands match up between bucket borders?
Simple. Prman does not create hair from displaced surfaces (or from any surface, for that matter).
It is up to the RIB translator (mtor, houdini, etc) to place each hair strand appropiately. Most likely, the translator does not bother about the displacements, and just grows hairs from the non-displaced object surface.
I imagine shadows might have a similar issue. If you had a long vein running across many buckets you might get shadow inconsistencies. How does PrMan handle this?
Using shadow maps, mainly. Shadows are generated as a prepass, taking into accout what each light sees, not what the camera sees, so whether the object is in view is no problem. You can, however, get small tesselation and floating point discrepancies between the light view and the camera view due to the size of your shadow map. This can lead to the usual artifacts of shadow maps (bias issues, lack of detail, too blurry, etc.). In practice, with decent settings, this is rarely a problem for most scenes.
When dealing with raytracing (like traced shadows), prman keeps two tesselations, both done in a view dependent manner (one for what the camera sees and one for what each ray sees, basically). You can find more info about that in the recent paper of Julian Fong, Per Christiansen and Dana Batali (available on Christiansen's web site).
01 January 2004, 04:17 PM
What's the website address? Google doesn't turn up anything of interest
01 January 2004, 05:26 PM
No surprise, as I mispelled Christensen's last name :)
01 January 2006, 05:00 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.