[Bf-committers] Subdivision Surfaces Proposal

[Lyndon Tremblay]

This is a very logical step. It would be unecessary to further allow 
Blender to be extended and implemented with operations and concepts 
requiring native and integrated edge data strutures. I have also been 
urging my thoughts toward native CSG tree foundations within Blender. 
Anyways, I can provide coding in the area you describe.

Matthew H. Plough wrote:
> Hello all:
> 
> Since many people have been complaining about the status of Blender's
> subdivision surfaces, I decided to investigate the ease with which the
> system could be made more powerful.  After reading "Subdivision Surfaces in
> Character Animation" by DeRose, Kass, and Truoung, I began looking at
> Blender's subdivision code, and found it very easy to extend.  However,
> fully implementing DeRose et al's semi-sharp Catmull-Clark subdivision
> surfaces will require a mesh data structure that stores edge data, something
> that Blender lacks.
> 
> Recently there has been a flurry of activity with edge-related features,
> such as edge loop selection, knife subdivision, and loop subdivision (not to
> be confused with Loop subdivision surfaces).  Right now, these features
> require weird hacks such as the HashEdge data structure for their
> implementation, and they don't work exactly as they should.  Since making
> them work with a vertex list and face list would require a huge amount of
> work, I suggest that we don't implement them with the current data
> structure.  Implementing a new data structure will require an equally huge
> amount of work, but the end result will be more extensible; it will allow
> addition of features such as semi-sharp subdivision surfaces as implemented
> in Pixar's short entitled "Geri's Game" and better decimation that uses edge
> collapses.
> 
> (a note: In the past, I have been yelled at for "requesting features." I am
> *not* requesting a feature.  I am *not* asking for someone to implement this
> for me.  I am willing to put in countless hours of programming, late into
> the night, to get this idea to see the light of day.)
> 
> Obviously, Blender's current vertex-list/indexed face list is not ideal for
> supporting current features, and some proposed features.  Therefore, any
> rewrite will require a lot of planning; we do not want to waste time
> developing another subpar data structure.  I would like to start discussion
> on the topic using the following background information:
> 
> Several options exist for a new type; the winged edge structure has been
> mentioned frequently, almost certainly because many Blender users have also
> used Wings3D.  However, the winged edge structure does not work for open
> meshes, or non-manifold meshes in general.  Any data type that cannot
> represent an open mesh would be useless in Blender; for example, the tube
> primitive could no longer be used if such a data type were implemented.
> Also, several users have mentioned situations where Blender would need to
> represent a non-manifold mesh; after certain remove doubles operations, for
> instance.  The winged edge structure would need heavy modification if it
> were to be used.  The same argument applies for the half edge or partial
> edge data structure.
> 
> However, S.H. Lee and K. Lee have developed a partial entity data structure
> that is specifically designed to compactly represent non-manifold meshes.
> The two goals of this data type coincide completely with Blender's
> methodology, so I suggest that this data structure be investigated further
> as a candidate for implementation.
> 
> I could probably implement such a structure on my own, but that would take
> an excessively long time, and would not involve a proper amount of input
> from other coders and the community in general.  Therefore, I would like to
> enlist some help -- are there any coders who are willing to help me with
> this project?
> 
> I thank you for your time spent reading this rather long email, and I hope
> that I will receive some feedback about this proposal's feasibility and
> timetable.
> 
> Sincerely,
> Matthew H. Plough
> mplough@princeton.edu
> 
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