var CursorRay = Viewport.PointToWorldRay(args.WindowPoint);
var ray = new Uno.Geometry.Ray();
ray.Direction = CursorRay.Direction;
ray.Position = CursorRay.Position;
var dist = Uno.Geometry.Distance.RayPoint(ray, center);
@simo: You might want to have a look at this branch. I should probably finish this stuff up (might already be done, I don’t quite remember the state I left it in) and merge it.
Sorry about breaking things for you. Please let me know if there’s anything else broken for you in this area.