[Bf-funboard] Subdividing Tris into tris (XSI Style)

Arne Schmitz arne.schmitz at gmx.net
Fri Jan 26 15:19:37 CET 2007

Am Freitag, 26. Januar 2007 15:03 schrieb Carsten Wartmann:
> Arne Schmitz wrote:
> > Am Freitag, 26. Januar 2007 04:40 schrieb ZanQdo:
> >> Hi, I love this feature of XSI subdivition, made a gif about it:
> >>
> >> http://dogfight.3developer.com/SubTris2Tris.gif
> >>
> >> it subdivides triangles to triangles instead of making quads and keeps a
> >> very smooth shape, could this be done with blender?
> >
> > Can you elaborate on that? Do you mean that instead of Catmull-Clark
> > Subdivision, blender should also offer Loop-Subdivision?
> Did you notice the image was a animated gif?

No, I did not. :) But now I have seen it.

> With that xsi option it was subdividing into tris along the last
> edgeloop. However I am not sure why it should be smoother then (at least
> not on a sphere?)

Ah yes, the problem with CC on triangle surfaces is, that it generates bad 
meshes with irregular vertices in the first iteration. Also the irregular 
vertices will be kept after more iterations. CC and Loop subdivision have 
both the property of being C^2 on all regular vertices, so for smoothness we 
want to avoid irregular vertices. There was a paper on this topic, that shows 
how to combine CC and Loop and how to join them in a C^2 manner:




Dipl.-Inform. Arne Schmitz              Phone   +49 (0)241 80-21817
Computer Graphics Group                 Fax     +49 (0)241 80-22899
RWTH Aachen University                  http://www.rwth-graphics.de
Ahornstrasse 55, 52074 Aachen, Germany
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