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There are two types of 3D polys in CGAL, Polyhedron, and Nef_polyhedron. The former allows one to specify an allocator as its fourth template:

http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Polyhedron/Chapter_main.html#Subsection_25.3.5

However, Nef_polyhedron_3 doesn't seem to have that.

What it does have however is iostream operators, to parse to/from an internal string representation:

https://github.ugent.be/divhaere/cgal/blob/master/include/CGAL/Nef_3/SNC_io_parser.h

But that is extremely slow indeed.

Looking at that SNC parser code however, it seems internally it still uses an allocator for its internal structure (an snc object). But even if I could get these to be allocated to my static buffer (to be passed to another process), I can't see anything in the Nef_polyhedron_3 constructors or accessor functions that allows me to reconstruct one.

EDIT: Looking into this a little further, I notice there IS a constructor from an SNC stucture https://github.ugent.be/divhaere/cgal/blob/master/include/CGAL/Nef_polyhedron_3.h :

Nef_polyhedron_3( const SNC_structure& W, SNC_point_locator* _pl, 
          bool clone_pl,
          bool clone_snc) {

And the SNC_structure uses allocators for its internal data (but not for itself):

https://github.ugent.be/divhaere/cgal/blob/master/include/CGAL/Nef_3/SNC_structure.h

Trouble is, that seems to only be set on a compile time basis - I only need to allocate to a specific buffer for polys I know I need to send to another process.

EDIT 2: I just noticed that one of the Nef_polyhedron_3 superclasses is Handle_for:

class Nef_polyhedron_3 : public CGAL::Handle_for< Nef_polyhedron_3_rep<Kernel_, Items_, Mark_> >, 
             public SNC_const_decorator<SNC_structure<Kernel_,Items_,Mark_> >

In there, that itself uses an allocator too:

https://github.ugent.be/divhaere/cgal/blob/master/include/CGAL/Handle_for.h

I'm still unclear how exactly I plug that in.

Marcos

Marcos Scriven
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1 Answers1

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Nef_polyhedron_3 currently doesn't support custom allocator. However, it is possible to make CGAL use a different allocator through the CGAL_ALLOCATOR macro. However, this will affect all CGAL headers which might be too much. However, it should be possible to add allocator support to the existing code without too much trouble.

pmr
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  • Thanks. As I say above, aware Nef'3 doesn't have custom allocator support. Also, I realise there is that macro (hence my comment about 'compile time' above). You say it should be possible to add without too much trouble, but I'm really looking for something more specific if possible. – Marcos Scriven Mar 28 '13 at 08:12
  • One further idea I had would be to go ahead and add the global CGAL_ALLOCATOR, but be able to set that to a certain mode. In default mode it would just delegate to a std::allocator. But in another mode, it would use the static buffer you had passed it before. – Marcos Scriven Mar 28 '13 at 08:14