CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 02/28/2014 04:09 PM, Zohar wrote:
> Wow, the whole thing (halfedge_collapse) is changed. Are there still 5 cases
> doing the same operations?

When there are no constrained edges it is the same. Otherwise, 
constrained edges cannot disappear.

> I don't fully follow.
> Record the neighborhood (a patch around the collapsed edge) before the
> collapse, and upon undo I simply cut this neighborhood from the coarse mesh
> and restore it to the way it was, sounds like a good idea.
> The thing is that I have additional data on the edges which needs to be
> updated if edges are collapsed (not related to the multi-resolution), so I
> still need to follow what happens and update my own data in the coarse mesh.
you'll know what happen because you must have a container storing
pending simplices.

> What do you mean by "modify halfedge_collapse", should I modify cgal sources
> or write a template instantiation override?
Modify the function halfedge_collapse so that the next/prev and
incidence relationships are updated but do not remove any simplex.

> What do you mean by "clean up the data structure from the pending
> simplices"? I assume it's related to the first step that leaves the
> simplicies, which are now actually deleted. But I don't see why the
> cut/paste patch idea needs all this.
The idea is to not remove any simplex so that handles are still valid.
You will have simplices not used in the structure however, which is
why you need to clean things when the undo is no longer required.

Sebastien.

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