New connection point function can be defined in the joint.connectionPoints namespace (e.g. joint.connectionPoints.myConnectionPoint) or passed directly as a function to the connectionPoint property of link source/target (or to the defaultConnectionPoint option of a paper).

In either case, the connection point function must return the connection point as a Point. The function is expected to have the form function(endPathSegmentLine, endView, endMagnet, args):

endPathSegmentLine g.Line The link path segment at which we are finding the connection point. If we are calling this method for a source connection point, it is the first segment (source anchor - first vertex, or source anchor - target anchor). If we are calling this method for a target connection point, it is the last segment (last vertex - target anchor, or source anchor - target anchor).
endView dia.ElementView The ElementView to which we are connecting. The Element model can be accessed as endView.model; this may be useful for writing conditional logic based on element attributes.
endMagnet SVGElement The SVGElement in our page that contains the magnet (element/subelement/port) to which we are connecting.
args object An object with additional optional arguments passed to the connection point method by the user when it was called (the args property).