private void drag_Rotate_Changed(DragListener drag)
{
Point currentPoint = Mouse.GetPosition(this.parent);
Vector deltaVector = Point.Subtract(currentPoint, this.centerPoint);
double angle = Vector.AngleBetween(this.startVector, deltaVector);
var destAngle = this.initialAngle + Math.Round(angle, 0);
if (!Keyboard.IsKeyDown(Key.LeftCtrl))
{
destAngle = ((int)destAngle / 15) * 15;
}
ModelTools.ApplyTransform(this.ExtendedItem, new RotateTransform()
{
Angle = destAngle
});
}