SubD rendering in mental ray?

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Old 01 January 2006   #1
SubD rendering in mental ray?

I was just wondering if anyone ever rendered real subD surfaces in mental ray? I mean the kind that will always render smooth no matter how close you zoom in, i.e view dependant tesselation, I know we can do this with nurbs in xsi but not for polys, my question is would it be worth using subD rendering at all, or is it better to just use "normal" polys when rendering in MR.

I recently tried prman and it has a nice subD mode for objects, they render fast and always look good, I somehow miss this in xsi.
 
Old 01 January 2006   #2
mentalray supports subdivision surfaces approximation flags.
they subdivide the surface based on criteria like parametric
iterations, length spatial and curvature distribution. xsi with
the v5 supports subdivision surfaces as geometry shaders
that will do the tesselletion at rendertime with no need for
big mi exported files. mentalimages itself develeped mentalmatter,
a special adaptive kind of smoothing surface method.


ciao
francesca
 
Old 01 January 2006   #3
Interesting, I wonder if such a geometry shader is available from ctrl. studio?

Also, if you use view dependant based on edge length, can it subdivide one part of the mesh more than other parts, like if I had a big mesh that had parts both near and far away from the cam, would it be able to tesselate the stuff further back much less compared to the stuff close to the cam?

I also heard that MR doesnt support n-gons for subD surfaces, is that still true?


Originally Posted by francescaluce: mentalray supports subdivision surfaces approximation flags.
they subdivide the surface based on criteria like parametric
iterations, length spatial and curvature distribution. xsi with
the v5 supports subdivision surfaces as geometry shaders
that will do the tesselletion at rendertime with no need for
big mi exported files. mentalimages itself develeped mentalmatter,
a special adaptive kind of smoothing surface method.


ciao
francesca
 
Old 01 January 2006   #4
Quote: Interesting, I wonder if such a geometry shader is available from ctrl. studio?
well a the geometry shader for runtime subd tesselation is already
in v5 as it comes with default installation. it is just that softimage added this thing
silently but you're already using geometry shaders to get your subd surfaces.


Quote: like if I had a big mesh that had parts both near and far away from the cam, would it be able to tesselate the stuff further back much less compared to the stuff close to the cam?
well yep, that's the point. I'm doing some tests here I will post
something when consistent.


ciao
francesca
 
Old 01 January 2006   #5
So how can I actually go ahead and use view dependant tesselation for polygon objects in XSI? I hope I wont have to hack the MI files.

Originally Posted by francescaluce: well a the geometry shader for runtime subd tesselation is already
in v5 as it comes with default installation. it is just that softimage added this thing
silently but you're already using geometry shaders to get your subd surfaces.


well yep, that's the point. I'm doing some tests here I will post
something when consistent.


ciao
francesca
 
Old 01 January 2006   #6
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