[vtk-developers] mysterious alpha plane problem

Michael Halle mhalle at bwh.harvard.edu
Thu Jul 7 11:47:22 EDT 2005


Since I checked in my changes to vtkWindowToImageFilter
to support reading back RGBA, the dashboard's showing
a problem with about half of the test machines.

The problem seems to be that the default OpenGL configuration
for windows sometimes has an alpha plane, and sometimes doesn't.
My machine (Mac running X11) has them on by default, so I didn't
see the problem.

That's okay, since you can explicitly ask for alpha planes using the
RenderWindow method AlphaBitPlanesOn.

However, when I turn this bit on just after creating the
render window (but before it actually gets mapped on-screen),
my machine can "no longer find a decent visual" (although,
of course, it can because it's doing it by default).  Window
creation fails, and the test segfaults.

It looks like there's no (other) test coverage on alpha
plane creation.

Has anyone encountered a problem like this one before?


Michael Halle
mhalle @ bwh.harvard.edu

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