This wraps the clipper library for performing boolean operations on polygons. Union, intersection, difference and xor are supported.
Forks
Forks pushed to more recently than mazbox/ofxClipper itself, plus any admin-confirmed fork with commits of its own — worth checking if you're hitting issues with the original.
README
ofxClipper
An addon for openframeworks that lets you do boolean operations on polygons (contours).
It does this by wrapping the clipper library (http://www.angusj.com/delphi/clipper.php)
ofxAddons