GPC – General Polygon Clipper library

The University of Manchester GPC library (wikipedia: GPC)
is a flexible and highly robust polygon set operations library for use with
C, C#, Delphi, Java, Perl, Python, Haskell, Lua, VB.Net (and other) applications.

Designer and implementor: Alan Murta | Licencing Manager: Toby Howard

GPC Features

Difference, intersection, exclusive-or and union clip operations are supported.
Polygons may be comprised of multiple disjoint contours.
Contour vertices may be given in any order - clockwise or anticlockwise.
Contours may be convex, concave or self-intersecting.
Contours may be nested (i.e. polygons may have holes).
Output may take the form of either polygon contours or tristrips.
Hole and external contours are differentiated in the result.
Coincident edges and degenerate regions are handled correctly.

GPC in action

The following examples show the results of GPC operations on two sets of polygons (Set 1: the United Kingdom and Ireland; Set 2: the four inward-pointing arrows). The operations are: difference (blue), intersection (green), exclusive-or (yellow) and union (purple).

Difference Intersection
Exclusive-or Union

GPC Licensing

GPC is free for downloading and time-unlimited evaluation by anyone.

Non-commercial use of GPC (for example: private / hobbyist / education)

GPC is free for non-commercial use only.
We invite non-commercial users to make a voluntary donation towards the upkeep of GPC.

Commercial use of GPC (for example: product development / commercial research)

If you wish to use GPC in support of a commercial product,
you must obtain an official GPC Commercial Use Licence from The University of Manchester.
Please email for details.

Download GPC

GPC v2.32 (zip, 28k). On-line documentation is here.

GPC demo for Windows

Maxim Shemanarev, developer of the Anti-Grain Geometry high quality rendering engine, has kindly donated this Windows application which shows GPC in action.

GPC demo for Linux

The gpctool package allows the interactive graphical evaluation of the GPC library under Unix / X11. Compilation requires the Mesa (or OpenGL) and xforms libraries - no precompiled binaries are available. The gpctool sources are available as either a Unix compressed tarfile (62k) or a PC Zip file (38k). Please note that this software is completely unsupported.

gpctool screenshot

GPC ports and wrappers

We thank these contributors for their GPC ports and wrappers:

ActionScript 3 port	Jakub Kaniewski
C# wrapper	Stefan Menne / Guido Bonino
Cocoa/NSBezier wrapper	Graham Cox
COM wrapper	Tom Wolf
Delphi/Pascal port (GPC v2.30)	Stefan Schedel
Delphi/Pascal port (GPC v2.32)	Richard B. Winston
haXe port	Michael Baczynski
Haskell port	Marco Túlio Gontijo e Silva
Java port	Daniel Bridenbecker
Lua binding	Luiz Henrique de Figueiredo
Octave binding	Rafael Laboissiere
Perl binding	Eric Wilhelm
Python bindings	Joerg Raedler
VB.NET wrapper	Tadej Basa

Other polygon clipping resources

Michael Leonov has compiled a comparison of polygon clippers, including GPC.
The comp.graphics.algorithms FAQ.
The UIUC Computational Geometry Pages.
Klaas Holwerda's Boolean, a C++ library.
David Kennison's Polypack, a FORTRAN library based on the Vatti algorithm.
Klamer Schutte's Clippoly, a clipper written in C++.
Michael Leonov's poly_Boolean C++ library, which extends the Schutte algorithm.
Dave Eberly's page on constructive planar geometry software.
CGAL, the Computational Geometry Algorithms Library.

GPC is free for non-commercial use only

If you are a non-commercial user and you have found GPC to be useful, we invite you to please make a donation and help support the continuation of this project. Thanks!

However, If you wish to use GPC in support of a commercial product, you must obtain an official GPC Commercial Use Licence from The University of Manchester. Please email for details.

Page last updated: 27 December 2012.