[vtkusers] vtkActor2D::LayerNumber and Overlays

[John Biddiscombe]

>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)

JB