Try point dragging.

dg.js example code

		var canvas = dg.Canvas("testcanvas", { border: "1px solid #ccc"});
		var axes = dg.Axes([canvas.width() / 4, canvas.height() / 1.5]).hide(false);
		
		var p1 = dg.Point([-1, -1]).label("A");
		var p2 = dg.Point([5, 2]).label("B");
		var p3 = dg.Point([7,-3]).label("C");
		var c = dg.Segment(p1, p2);
		var b = dg.Segment(p2, p3);
		var a = dg.Segment(p3, p1);
		var sa = dg.AngleBisector(p2,p1,p3);
		var sb = dg.AngleBisector(p3,p2,p1);
		var sc = dg.AngleBisector(p1,p3,p2);
		var o = dg.Intersect(sa,sb).label("O");
		var pl = dg.PerpendicularLine(o, b);
		var r = dg.Intersect(pl, b).label("r");
		var incircle = dg.Circle(o, r);