[vtkusers] "Disabling" a volume rendering pipeline in a controlled way?

[Elvis Stansvik]

Hi,

I have a volume rendering pipeline set up. In response to user
interactions, I can manipulate certain aspects of the pipeline and
re-render. I can even set the filename of the reader that I use as a
source, to completely change out the volume being rendered.

But what if I want to completely disable the pipeline, in effect unsetting
the filename of the reader.

My pipeline is basically just HDF5Reader -> vtkGPUVolumeRayCastMapper,
where HDF5Reader is a custom reader I wrote to read volumes from a HDF5
file.

The problem is I can't just setFileName(None) on my reader, because my
custom reader has a

        if self._fileName is None:
            return 0

in its RequestData and RequestInformation, and I will thus get errors from
VTK saying the pipeline failed if I do this.

So my question is: What is the proper way of "unhooking" (or "disabling" if
you will) a pipeline? I want the render window to simply show empty space
when in this state, but still have the entire pipeline intact and ready for
when I next want to set the filename of the reader to a valid volume.

Thanks in advance,
Elvis
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