[vtkusers] Bug in vtkRenderWindow

[John Shalf]

You should expect this behavior from any system that uses 3D hardware acceleration.  When you
do glReadPixels() (for instance), it actually grabs the contents of the framebuffer
directly... that includes anything that is obscuring the section of the framebuffer being read
(ie. your renderwindow).  I used to see this sort of thing with AVS too.  I don't think
there's much you can do about it except to hide an offscreen renderer operation somewhere when
exec WritePPMImageFile.  This is a problem that motivates a lot of the work on the offscreen
render windows.

-john

Erik Sobel wrote:

> There seems to be a bug in vtkRenderWindow::WritePPMImageFile (vtk 3.1.1 /
> Win-NT sp4)
>
> vtkRenderWindow::WritePPMImageFile - saves a ppm image of the renderWindow
> if the window is on top but, if the window is partially or totally obscured
> you get a ppm of whatever screen graphics are within the boundaries of the
> render window - this could be windows from other apps, menu bars - whatever
> is in the client area of the renderWindow.  It's kind of cool - like a
> handy screen capture utility.
>
> -Erik
>
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