[vtk-developers] ImageSampleDistance not used in vtkOpenGLGPURayCastMapper?

[Ken Martin]

For Virtual Reality and 4K/5K displays I believe ImageSampleDistance (or
similar adjustable X,Y sample rate) has to be supported. Not sure when it
will get implemented but I personally think it is necessary.

Thanks
Ken


On Tue, Feb 14, 2017 at 1:52 AM, Elvis Stansvik <
elvis.stansvik at orexplore.com> wrote:

> 2017-02-13 17:10 GMT+01:00 Sankhesh Jhaveri <sankhesh.jhaveri at kitware.com>
> :
> > 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.
>
> Ah, that explains it.
>
> >
> > That being said, do you have a specific use case for
> ImageSampleDistance? We
> > could explore options for adding the feature back in.
>
> I don't have a specific use case for it really. The reason I started
> looking into how the auto-adjustment works is that I've found it to be
> a little too aggressive in reducing the quality. I found that if I
> turned off auto-adjustment and hardcode the sample distance, I could
> get acceptable interactive frame rate at reasonable zoom level with a
> quality that looked better than what happens when the auto-adjustment
> kicks in. So I started looking at how the auto-adjustment works, and
> if perhaps I could make my own heuristic for degrading the quality. I
> was thus interested in what knobs for quality were available to me.
>
> I think what I'm really looking for is some way of setting a lower
> bound on the actual sample distance along the ray
> (ActualSampleDistance internally), similar to
> MinimumImageSampleDistance but for the sample distance.
>
> Has anyone else found that the auto-adjustment is seemingly a bit too
> aggressive? I'm keeping the desired frame rate of the render window at
> the default (15 fps I think), but the quality during interaction
> degrades to an unnecessary extent I think..
>
> Elvis
>
> >
> > 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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> >>
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> >>
> > --
> >
> > Sankhesh Jhaveri
> >
> > Sr. Research & Development Engineer | Kitware | (518) 881-4417
> _______________________________________________
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>


-- 
Ken Martin PhD
Chairman & CFO
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065
518 371 3971

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