Initial commit

README.md

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 # GeneralPolygonClipper
 General Polygon Clipper, aka GPC, version 2.32
+
+See GPC-README.pdf for more official information about this library.
+
+GPC was discontinued in August of 2020 with the following note on the website:
+
+> As of August 2020, GPC is no longer distributed or available.
+
+This begged the questions of, how do you get GPC? And, what is the licensing now?
+
+On Twitter, we were able to get ahold of Toby Howard who had this to say:
+
+> I was the licensing manager for GPC. In 2020 the author of the software decided to withdraw its official distribution. If you obtain a copy of GPC from another source you can use it without any licensing requirement. I've updated Wikipedia to clarify. Hope this helps.
+
+https://twitter.com/tobyhoward/status/1473722153849786381
+
+I'm therefore placing this onto GitHub under the MIT License. If Alan Murta, Toby Howard, or the University of Manchester would like me to remove it, just ask and I'll respect your wishes.

VERSIONS.TXT

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+
+Generic Polygon Clipper (gpc) Revision History
+==============================================
+
+
+v2.32   17th Dec 2004
+---------------------
+    Fixed occasional memory leak occurring when processing some
+    degenerate polygon arrangements.
+    Added explicit type casting to memory allocator in support of
+    increased code portability.
+
+v2.31    4th Jun 1999
+---------------------
+    Separated edge merging measure based on a user-defined GPC_EPSILON
+    value from general numeric equality testing and ordering, which now
+    uses direct arithmetic comparison rather an EPSILON based proximity
+    test.
+    Fixed problem with numerical equality test during construction of
+    local minima and scanbeam tables, leading to occasional crash.
+    Fixed hole array memory leak in gpc_add_contour.
+    Fixed uninitialised hole field bug in gpc_polygon_clip result.
+
+v2.30   11th Apr 1999
+---------------------
+    Major re-write.
+    Minor API change: additional 'hole' array field added to gpc_polygon
+    datatype to indicate which constituent contours are internal holes,
+    and which form external boundaries.
+    Minor API change: additional 'hole' argument to gpc_add_contour
+    to indicate whether the new contour is a hole or external contour.
+    Minor API change: additional parameter to gpc_read_polygon and
+    gpc_write_polygon to indicate whether or not to read or write
+    contour hole flags.
+    Fixed NULL pointer bug in add/merge left/right operations.
+    Fixed numerical problem in intersection table generation.
+    Fixed zero byte malloc problem.
+    Fixed problem producing occasional 2 vertex contours.
+    Added bounding box test optimisations.
+    Simplified edge bundle creation, detection of scanbeam internal
+    edge intersections and tristrip scanbeam boundary code.
+    Renamed 'class' variable to be C++ friendly.
+
+v2.22   17th Oct 1998
+---------------------
+    Re-implemented edge interpolation and intersection calculations
+    to improve numerical robustness.
+    Simplified setting of GPC_EPSILON.
+
+v2.21   19th Aug 1998
+---------------------
+    Fixed problem causing occasional incorrect output when processing
+    self-intersecting polygons (bow-ties etc).
+    Removed bug which may lead to non-generation of uppermost triangle
+    in tristrip output.
+
+v2.20   26th May 1998
+---------------------
+    Major re-write.
+    Added exclusive-or polygon set operation.
+    Replaced table-based processing of edge intersections with
+    rule-based system.
+    Replaced two-pass approach to scanbeam interior processing with
+    single pass method.
+
+v2.10a  14th May 1998
+---------------------
+    Minor bug-fixes to counter some v2.10 reliability problems.
+
+v2.10   11th May 1998
+---------------------
+    Major re-write.
+    Incorporated edge bundle processing of AET to overcome coincident
+    edge problems present in previous releases.
+    Replaced Vatti's method for processing scanbeam interior regions
+    with an adapted version of the scanbeam boundary processing
+    algorithm.
+
+v2.02   16th Apr 1998 (unreleased)
+----------------------------------
+    Fixed internal minimum vertex duplication in gpc_polygon_clip
+    result.
+    Improved line intersection code discourage superfluous
+    intersections near line ends. 
+    Removed limited precision number formatting in gpc_write_polygon.
+    Modification to allow subject or clip polygon to be reused as the
+    result in gpc_polygon_clip without memory leakage.
+
+v2.01   23rd Feb 1998
+---------------------
+    Removed bug causing duplicated vertices in output polygon.
+    Fixed scanbeam table index overrun problem.
+
+v2.00   25th Nov 1997
+---------------------
+    Major re-write.
+    Replaced temporary horizontal edge work-around (using tilting)
+    with true horizontal edge handling.
+    Trapezoidal output replaced by tristrips.
+    gpc_op constants now feature a `GPC_' prefix.
+    Data structures now passed by reference to gpc functions.
+    Replaced AET search by proxy addressing in polygon table.
+    Eliminated most (all?) coincident vertex / edge crashes.
+
+v1.02   18th Oct 1997 (unreleased)
+----------------------------------
+    Significantly reduced number of mallocs in build_lmt. 
+    Scanbeam table now built using heapsort rather than insertion
+    sort.
+
+v1.01   12th Oct 1997
+---------------------
+    Fixed memory leak during output polygon build in
+    gpc_clip_polygon.
+    Removed superfluous logfile debug code.
+    Commented out malloc counts.
+    Added missing horizontal edge tilt-correction code in
+    gpc_clip_polygon.
+
+v1.00   8th Oct 1997
+--------------------
+    First release.
+