private void UpdateBoundsItem()
 {
     if (Children.Count == 2)
     {
         var transformAabb = TransformItem.GetAxisAlignedBoundingBox();
         var fitAabb       = FitBounds.GetAxisAlignedBoundingBox();
         var fitSize       = fitAabb.Size;
         if (boundsSize.X != 0 && boundsSize.Y != 0 && boundsSize.Z != 0 &&
             (fitSize != boundsSize ||
              fitAabb.Center != transformAabb.Center))
         {
             FitBounds.Matrix *= Matrix4X4.CreateScale(
                 boundsSize.X / fitSize.X,
                 boundsSize.Y / fitSize.Y,
                 boundsSize.Z / fitSize.Z);
             FitBounds.Matrix *= Matrix4X4.CreateTranslation(
                 transformAabb.Center
                 - FitBounds.GetAxisAlignedBoundingBox().Center);
         }
     }
 }