/// <summary>
/// Called when geometry has been changed.
/// </summary>
protected override void OnModelChanged()
{
var mb = new MeshBuilder();
var p0 = this.Offset;// new Vector3(0, 0, 0);
var d = this.Direction;
d.Normalize();
var p1 = p0 + (d * (float)this.Length);
mb.AddArrow(p0, p1, this.Diameter, 2, 64);
this.Geometry = mb.ToMeshGeometry3D();
}