[vtkusers] Bug with vtkPropPicker and overlapping renderers

[Simon Drouin]

Trying to get the pick position from the first of 2 overlapping renderers
doesn't work. Here is an example:

vtkRenderer * ren0 = vtkRenderer::New();
ren0->SetLayer( 0 );
vtkRenderer * ren1 = vtkRenderer::New();
ren1->SetLayer( 1 );

vtkRenderWindow * win = vtkRenderWindow::New();
win->AddRenderer( ren0 );
win->AddRenderer( ren1 );

......

vtkPropPicker * picker = vtkPropPicker::New();
picker->Pick( x, y, z, ren0 );
double pos[3];
picker->GetPickPosition( pos );

Here, pos will be wrong. The reason seems to be that GetPickPosition()
relies on the content of the z buffer, but the z buffer generated by the
first renderer is being cleared when the second renderer gets rendered.

Anybody has a workaround for that?

s.
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