Subdivision Surfaces

[Bill Lorensen]

Folks,
	I've added 5 new classes to vtk that support subdivision surfaces. 
Subdivision is a hot new modeling technique that could someday displace 
Nurbs as a smooth surface modeler. There is lots of info on the web and in 
recent Siggraph proceedings. There was an excellent course at Siggraph this
year on the topic.

Subdivision surfaces use simple rules to create new vertices from a 
polygonal control net. The same subdivision rules can be applied to any 
point data (scalars, normals, texture coords, etc.). Each subdivision step 
produces 4 times the number of input triangles. Currently, the implemented 
filters only handle triangles (and not triangle strips) so you should place
a vtkTriangleFilter in the pipeline if your data has strips or polygons.

I'm interested in seeing how these surfaces can be applied to visualization.

The new classes are:
vtkApproximatingSubdivisionFilter
vtkInterpolatingSubdivisionFilter
both of these are abstract

vtkLinearSubdivisionFilter
vtkButterflySubdivisionFilter
these are both interpolating

vtkLoopSubdivisionFilter
is approximating.

I hope to add a Catmul/Clark filter by the end of the year.

There are several examples in graphics/examplesTcl to illustrate the filters.

Bill





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