[Bf-committers] BMesh operator questions

Howard Trickey howard.trickey at gmail.com
Sat Mar 17 12:06:56 CET 2012

On Sat, Mar 17, 2012 at 1:10 AM, Campbell Barton <ideasman42 at gmail.com>wrote:

> On Sat, Mar 17, 2012 at 2:09 PM, Nicholas Bishop
> <nicholasbishop at gmail.com> wrote:
> > A couple of BMesh questions I could use some guidance on:
> >
> > 1. Is it safe to hang on to element pointers after running an
> > operator? E.g. if I have a BMFace pointer, then run a BMesh operator
> > that can add faces, but never delete them, is my BMFace pointer still
> > guaranteed to be valid?
> Yes the pointers remain valid, but worth noting - the way BLI_mempool
> works it can add faces in free slots of existing chunks - so a face
> may be added *before* existing faces.
> The pointer will be valid but the index may change.
> > 2. Can operator slots of type 'buffer' be filled without using oflags
> > or hflags? Something akin to BMO_slot_map_insert() I guess, but for
> > buffers. I ask because it seems like using flags will force a lot of
> > operations to be linear (relative to the number of elements) where
> > they might otherwise be constant. E.g. maybe I already have an array
> > of the three edges I want to put in a buffer slot, but instead I have
> > to set a flag for the three edges, then internally all edges' flags
> > must be checked? Unless internally it is doing something to avoid
> > checking all edges?
> Its not done much (at all?) but think it would be fine to just add
> elements with BMO_slot_map_insert() directly, probably some parts of
> our code could be optimized by doing this.
> The bmesh operator code is not totally optimal anyway - the way it
> allocates flags and frees per call, and uses flags - seems like its
> intended for convenience more then speed.

But I agree with the implied sentiment that one of the goals of bmesh was
(I think) to add local neighbor information so that, as far as possible,
operations should take O(f(n)) rather than O(f(N)) where n is the size
of the affected and/or selected mesh and f is some reasonable function.
The code is far from there now, but would be good to try to get it there
some day, so that editing a mesh with many millions of vertices will
feel snappy.  But it would require a bunch of work on how selections
and visibility information is kept and cached to make this a reality.

> > Thanks,
> > -Nicholas
> > _______________________________________________
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> > http://lists.blender.org/mailman/listinfo/bf-committers
> --
> - Campbell
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