2D polygon operations library licence problem

  • AlexR

    AlexR - 2011-12-29

    Hi guys

    I have just been scouring the FAQ and i came across this:

    Why can't the pocketing algorithm handle simple holes/islands?

    "Sadly both major libraries offering 2D polygon operations (CGAL and GPC) are distributed under GPL-incompatible licenses. It is a real pity (and a huge waste of development resources) that their authors prefer to distinguish between commercial and non-commercial use, which makes this software unsuitable for any Free Software. If you know of any GPL-compatible library for polygon handling (ideally with bindings for Python) then just drop us a mail!"

    OK…. most of use use InkScape or blender and they both have boolean operations (2D polygon operations) and as far as I know Inkscape and blender are both open source software.

    So question for the developers of pycam. Could you raid their libraries or code and use/modify them?

    Just asking…..?


  • Lars

    Lars - 2012-01-03

    Hi alexr,

    I took a short look at the build requirements of Inkscape and I did not see a suitable geometry library in the list. Digging into the code will probably reveal custom code that usually works. But this would involve a port of this code from C++ to Python. Additionally the offsetting problem is not trivial enough, that Inkscape's (or Blender's) code could be considered to be final. Thus it will require maintenance …
    To put it simply: I am a bit tired of trying to adapt or write non-trivial polygon-related code. Currently I am in the mood to just wait for a suitable library to pop up. This would solve the problem.

    Recently I stumbled upon Clipper: http://www.angusj.com/delphi/clipper.php
    The license is ok - but the packaging is really cumbersome.
    Here someone ("alexrj" - but that's not you - or?) wrote Perl bindings for clipper: https://github.com/alexrj/Math-Clipper.
    Maybe I will find the time during the next months to write Python bindings as well. Then we will have the Clipper library in PyCAM - which should solve all of these problems.
    Or would someone else like to pick up this task? This would be awesome!


  • Angus Johnson

    Angus Johnson - 2012-01-22

    The license is ok - but the packaging is really cumbersome.

    I'm wondering why you consider the packaging 'cumbersome'? How would you like it packaged?
    Angus (author of Clipper)

  • Lars

    Lars - 2012-01-22

    Hi Angus,

    thanks a lot for joining this discussion!

    I hope that you didn't consider my wording as too offensive - I was just surprised that I did not manage to compile the library within a few minutes :)
    Taking a quick look at it, I was missing the following things:
    - a README/INSTALL file describing the build process
    - a Makefile (or any other build file format)
    - maybe a header file

    But I am not a real expert in C/C++ - thus I don't really know the common ways of distribution. I am more or less just used to the ./configure-make-cycle …

    btw: is there a kind of "reference" implementation of clipper in any language? Or do you try to keep all ports (C++/C#/Delphi) in sync?

    Anyway: your library looks very promising and seems to be full of features!


  • Angus Johnson

    Angus Johnson - 2012-01-22

    Hi Lars.
    No, I really didn't find your wording offensive, and I'm very conscious of just how easy it is to misinterpret the emotional tone of online posts. So no worries there :).
    I'm no C/C++ expert either. In fact, this library is my first foray into C/C++ and I'm still not up to speed on Makefiles hence that deficiency. Anyhow, I'm open to suggestions/help on rectifying that too :).

  • kishchak

    kishchak - 2012-11-13

    See the PolygonLib - Polygon Clipping Library.

  • kishchak

    kishchak - 2012-11-13

    See the PolygonLib - Polygon Clipping Library.

  • Lars

    Lars - 2012-11-13

    Hi kishchak,

    thanks for your comment, but PolygonLib does not seem to be available under a libre software licence. Thus it cannot be used by PyCAM.

    But there was a change from another direction: the CGAL library recently switched their licence to the GPL. Thus this will probably be the library of choice for PyCAM (as soon as someone starts to work on it).



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