Dragging tool performs distance tests for all applied points.

const drag = new Dragging
drag.initDragging(this)
drag.onDragMove = this.onDragMove.bind(this)
drag.onDragEnd = this.onDragEnd.bind(this)

Install points into the map:

drag.addPoints(this.center, this.point0, this.point1)

Upon a mouse action we can access the discovered points.

let p = drag.getPoint();
if(p) {
    p.pen.circle(ctx)
}