[vtkusers] vtkActor2D::LayerNumber and Overlays

[Hank Childs]

> >vtkRenderer::SetLayer(layerNum)
> >+
> >vtkRenderWindow::SetNumberOfLayers(totalNumLayers)
> 
> Aha. Splendid. This begs the question...Why does Actor2D have a layernum at 
> all, if each renderer can have a layer? Is the Actor2D::layernumber used 
> anywhere (he asks knowing a quick grep will tell him...[pause] grep reveals 
> that no code anywhere uses the Actor2D layernumber. Puzzled? Yes I am. Why 
> is it there?)
> 
> Thanks for the renderer info. I just found (in the old tree, your 
> layers.cxx which [pause again] runs OK. I'll play with it)

Hello John,

My guess is that vtkActor2D still has a layer number because of sloppiness
on my part.  I added the layering code to the renderer, which (I believe)
is more general than the layering code for the 2D actors.  I can only
assume that I didn't pull the layering code for 2D actors (if I realized
that its functionality was subsumed at the time), because there are always
concerns about changing interfaces and breaking client programs.

Just as an aside, I did want to render 3D things in layers.  This one
wasn't what I needed, but I heard a good use recently: having an X-Y-Z
triad off on the corner in front of the "real" 3D dataset.

Best regards,
Hank

____________________________________________________________________________

Hank Childs
VisIt/MeshTV
Lawrence Livermore National Laboratory

email: childs3 at llnl.gov