Question

Is it possible to restrict the drag source to only move within the boundaries of a circular path when dragging it?

Answer 1

You don’t need the 360-point path. Instead, as you are dragging, compute the current angle using Math.Atan2(Y,X), and then generate the point on the circle. You would still need to compute center and radius on resize and store them, or compute them inside MouseMove.

    private void UserControl_MouseMove(object sender, MouseEventArgs e)
    {
        if (!isDraggingMarker)
            return;
        var position = e.GetPosition(this);

        double angle = Math.Atan2(position.Y - center.Y, position.X - center.X);
        var closest = new Point(center.X + radius*Math.Cos(angle),
                                center.Y + radius*Math.Sin(angle));

        SetMarkerPosition(closest);
    }