Clipper - an open source freeware polygon clipping library.

The Clipper library performs boolean clipping - intersection, union, difference & exclusive-or - on 2D polygons. It also performs polygon offsetting. The library accepts all types of polygons including complex (self-intersecting) polygons; polygons with holes; and even polygons with co-linear edges. The library is based on Vatti's clipping algorithm.

The download package contains the library's full source code (written in Delphi, C++, C# and Python), numerous demos, a help file and links to third party Perl, Ruby and Haskell modules.

Version: 5.1.4
Last updated: 24 March 2013
Freeware for both open source and commercial applications (Boost Software License).
Copyright © 2010-2013 Angus Johnson











Clipper's features compared with 3 other polygon clipping libraries:
  Speed tests* (faster is better) ... Features ... Cost
  Classic 174239¹ Ellipses & Fan Ellipses & Rectangles Overlap Stars Complex Polygons² Supports complex polygons Miscellaneous Free for commercial use
General Polygon Clipper 2785 ms 112 ms 125 ms 31 ms Multiple errors³ Yes Last updated Dec 2004 No
PolyBool 835 ms 138 ms 174 ms 28 ms N/A No Last updated Jun 2006 No
Boost Geometry 78 ms 43 ms 33 ms 25 ms N/A No C++ only
Depends on Boost Library		 Yes
Clipper 113 ms 31 ms 36 ms 9 ms No errors Yes C++;C#;Delphi
Python;Javascript
Polygon Offsetting		 Yes

* Speed tests were performed using the latest versions of all software as published on the respective websites (as of 11 April 2013). The benchmark test utility with full source code can be downloaded here. Tests were performed on a PC with 2.53 gigahertz Intel Core2 Duo P8700 processor with 4GB RAM running Window 7 Professional.
¹ The 'Classic 174239' test uses a test data sample from the PolyBoolean website here.
² The 'Complex Polygons' test consists of intersecting a single subject and single clip polygon with random vertices. Coordinates are rounded to multiples of 10 to substantially increase the frequency that more than two edges intersect at a given point. This "stress-tests" the clipping algorithms. (PolyBoolean and Boost Geometry could not be tested since they do not allow boolean operations on complex polygons.)
³ The errors in GPC's random polygon test are unhandled exceptions that result in a failure of the clipping operation.

An independent test of multiple polygon clipping libraries can be found here:
http://rogue-modron.blogspot.com/2011/04/polygon-clipping-wrapper-benchmark.html



Code snippets showing how to use the Clipper library to do a polygon intersection ...

C++
	#include "clipper.hpp"
	
	//from clipper.hpp ...
	//typedef signed long long long64;
	//struct IntPoint {long64 X; long64 Y;};
	//typedef std::vector<IntPoint> Polygon;
	//typedef std::vector<Polygon> Polygons;
	...
	using namespace ClipperLib;
	
	Polygons subj(2), clip(1), solution;
	
	//define outer blue 'subject' polygon
	subj[0].push_back(IntPoint(180,200));
	subj[0].push_back(IntPoint(260,200));
	subj[0].push_back(IntPoint(260,150));
	subj[0].push_back(IntPoint(180,150));
	
	//define subject's inner triangular 'hole' (with reverse orientation)
	subj[1].push_back(IntPoint(215,160));
	subj[1].push_back(IntPoint(230,190));
	subj[1].push_back(IntPoint(200,190));
	
	//define orange 'clipping' polygon
	clip[0].push_back(IntPoint(190,210));
	clip[0].push_back(IntPoint(240,210));
	clip[0].push_back(IntPoint(240,130));
	clip[0].push_back(IntPoint(190,130));
	
	DrawPolygons(subj, 0x160000FF, 0x600000FF); //blue
	DrawPolygons(clip, 0x20FFFF00, 0x30FF0000); //orange
	
	//perform intersection ...
	Clipper c;
	c.AddPolygons(subj, ptSubject);
	c.AddPolygons(clip, ptClip);
	c.Execute(ctIntersection, solution, pftNonZero, pftNonZero);
	DrawPolygons(solution, 0x3000FF00, 0xFF006600); //solution shaded green


Delphi
	uses Clipper;
	...
	var
	  i: integer;
	  subj, clip, solution: TPolygons;
	begin
	  setlength(subj, 2);
	  setlength(subj[0], 4);
	  subj[0][0] := IntPoint(180,200);
	  subj[0][1] := IntPoint(260,200);
	  subj[0][2] := IntPoint(260,150);
	  subj[0][3] := IntPoint(180,150);
	  
	  setlength(subj[1], 3);
	  subj[1][0] := IntPoint(215,160);
	  subj[1][1] := IntPoint(230,190);
	  subj[1][2] := IntPoint(200,190);

	  setlength(clip, 1);
	  setlength(clip[0], 4);
	  clip[0][0] := IntPoint(190,210);
	  clip[0][1] := IntPoint(240,210);
	  clip[0][2] := IntPoint(240,130);
	  clip[0][3] := IntPoint(190,130);
	  
	  DrawPolygons(subj, $160000FF, $600000FF);
	  DrawPolygons(clip, $20FFFF00, $30FF0000);
		
	  with TClipper.Create do
	  try
	    AddPolygons(subj, ptSubject);
	    AddPolygons(clip, ptClip);
	    Execute(ctIntersection, solution, pftNonZero, pftNonZero);
	    DrawPolygons(solution, $3000FF00, $FF006600);
	  finally
	    free;
	  end;
	  
	end;


C#
	using ClipperLib;
	
	using Polygon = List<IntPoint>;
	using Polygons = List<List<IntPoint>>;
	...
	Polygons subj = new Polygons(2);
	subj.Add (new Polygon(4));
	subj[0].Add(new IntPoint(180, 200));
	subj[0].Add(new IntPoint(260, 200));	
	subj[0].Add(new IntPoint(260, 150));
	subj[0].Add(new IntPoint(180, 150));

	subj.Add(new Polygon(3));
	subj[1].Add(new IntPoint(215, 160));
	subj[1].Add(new IntPoint(230, 190));	
	subj[1].Add(new IntPoint(200, 190));

	Polygons clip = new Polygons(1);
	clip.Add(new Polygon(4));
	clip[0].Add(new IntPoint(190, 210));
	clip[0].Add(new IntPoint(240, 210));	
	clip[0].Add(new IntPoint(240, 130));
	clip[0].Add(new IntPoint(190, 130));

	DrawPolygons(subj, Color.FromArgb(0x16, 0, 0, 0xFF), 
	  Color.FromArgb(0x60, 0, 0, 0xFF));
	DrawPolygons(clip, Color.FromArgb(0x20, 0xFF, 0xFF, 0), 
	  Color.FromArgb(0x30, 0xFF, 0, 0));

	Polygons solution = new Polygons();

	Clipper c = new Clipper();
	c.AddPolygons(subj, PolyType.ptSubject);
	c.AddPolygons(clip, PolyType.ptClip);
	c.Execute(ClipType.ctIntersection, solution, 
	  PolyFillType.pftEvenOdd, PolyFillType.pftEvenOdd);
	DrawPolygons(solution, Color.FromArgb(0x30, 0, 0xFF, 0), 
	  Color.FromArgb(0xFF, 0, 0x66, 0));


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