[vtkusers] Overlaping view props in a rendered

[Thompson, David C]

> Hi Gerrick, thanks but I don't think that is exactly what I am after
> as my data exactly overlaps.
> I have a vtkUnstructuredGrid of which I select a portion of and
> create a new vtkUnstructuredGrid from.  Thus I have the original
> grid and then a second subsampled grid.  I want to draw the original
> grid with the selected grid on top so the cells will actually overlap
> exactly but each grid has a different lut so you can see the selected
> portion.

Hi Sarah,

    Take a look at vtkMapper::SetResolveCoincidentTopology(). It uses
OpenGL's glPolygonOffset() to move the geometry slightly towards
the camera. It isn't perfect because it takes a couple of parameters
that aren't always easy to choose appropriately, but it works
relatively well.

    David