[vtk-developers] ImageSampleDistance not used in vtkOpenGLGPURayCastMapper?

[Sankhesh Jhaveri]

Hi Elvis,

The ImageSampleDistance property was left out when coming up with the new
OpenGL2 volume mapper to avoid an additional step of rendering the volume
to an FBO and then using the texture to compute the scaling. This
simplifies the code path and reduces the extra performance overhead. The
documentation could have been better on this. We'll update it.

That being said, do you have a specific use case for ImageSampleDistance?
We could explore options for adding the feature back in.

Thanks,
Sankhesh
​

On Mon, Feb 13, 2017 at 6:55 AM Elvis Stansvik <elvis.stansvik at orexplore.com>
wrote:

> 2017-02-13 12:54 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> > I was digging through the code trying to understand how the
> > auto-adjustment of sample distance and image sample distance takes
> > place in the GPU volume ray cast mapper. From the looks of it, the
> > ImageSampleDistance is not respected by this mapper, even in the
> > non-automatic case, or am I missing something?
>
> Sorry, with "non-automatic case" I mean when AutoAdjustSampleDistance is
> Off.
>
> Elvis
>
> >
> > The only role ImageSampleDistance seems to play for this mapper is
> > when the reduction factor is calculated (when auto-adjustment is
> > turned off):
> >
> >   if ( !this->AutoAdjustSampleDistances )
> >   {
> >     this->ReductionFactor = 1.0 / this->ImageSampleDistance;
> >     return;
> >   }
> >
> > Elvis
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Sankhesh Jhaveri *Sr. Research & Development Engineer* | Kitware
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​
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