This solves a limitation that EdgesGeometry has. EdgesGeometry can’t be used to find cluster of faces and the proper edges associated with them based on a threshold angle.
The geometry adds
Face3.regionIndex for interactivity. The faces of a region can be accessed using
RegionGeometry.regions[ Face3.regionIndex ] .
The regions and edges can be updated using
RegionGeometry.update( thresholdAngle ) .
I use it for flood filling the faces in my paint app.