[vtk-developers] Unstructured Volume Rendering Mesa support

[Randall Hand]

Well, I'll admit that I made that statement based on the fact that the
vtkVolumeRenderingFactory seems to have no knowledge of the other volume
renderers.

>From my tests:
    * The new vtkProjectedTetrahedraMapper runs in approx 9s with good
results.
    * Simply s/vtkProjectedTetrahedraMapper/vtkUnstructuredGridVolumeZSweepMapper/g
and running takes 18minutes, and gives good results.
    * Then simply %s/ZSweep/RayCast/g and running takes about 18seconds, and
gives ok results (I do get a render, but there seems to be a degenerate case
error along the axes.. I get blank 1-pixel lines on the horizontal &
vertical at the exact center of the image).

So I was mistaken on that at least :)  Odd how the other two can magically
make the Mesa/OpenGL switch but the projectedTet can't.  Oh well.  How do
you want the patch?


On 4/4/06, Lisa Avila <lisa.avila at kitware.com> wrote:
>
>
> Hi Randall,
>
> I will handle the patch. Yes - this was a known problem that was
> (admittedly quite low down) on my "to do" list - thank you for taking the
> time to make the fix.
>
> You say that "none of the new unstructured volume renderers properly
> support Mesa" - have you encountered problems with more than just the PT
> mapper? I believe the ray caster works (uses the same code - structured and
> unstructured - to display the results), and the ZSweep mapper uses this code
> as well. Please let me know if you are having problems with those classes.
>
> Lisa
>
>
>
>
> At 09:26 AM 4/4/2006, Randall Hand wrote:
>
> (For those of you who've dug through this already on the vtk-users, I am
> sorry.  Just want to make sure the right people get their eyeballs on this).
>
> I've been trying to do some volume rendering on an in-house dataset and
> it's been giving me nothing but trouble.  I finally broke down and wrote a
> simple driver app to do nothing but volume rendering & save the result to a
> PNG on disk, and came to a few surprising conclusions.  Basically,
> vtkProjectedTetrahedraMapper doesn't work with mangled mesa.  I can remove
> the "UseMesaClasses" from the beginning of the code and everything works
> just fine but it does throw a window on the screen.  Add them back, and all
> I get is empty space for outputs.
>
> Ok, after alot of digging I found the problem. It seems that none of the
> new unstructured volume renderers properly support Mesa. My best guess is
> that it was setting up the scene with mangled-mesa contexts, and then the
> Volume Rendering was using true OpenGL.  Every command probably returned an
> error (no GL context), but nothing checks it, so it rendering blindly &
> ignorant of what was going on.
>
> After alot of work, I managed to apply the same structure as the other
> objects to the vtkProjectedTetrahedraMapper successfully. There is now a
> vtkProjectedTetrahedraMapper that, with the help of the
> vtkVolumeRenderingFactory, can properly instantiate either a
> vtkOpenGLProjectedTetrahedraMap
> per or a vtkMesaProjectedTetrahedraMapper.  >From the testing I've done
> here (with the hello-world code shown originally), I've been able to switch
> between the two pretty easily and get almost identical results.  There are a
> few discrepancies, but since this is a hardware accelerated version it's
> very susceptible to the fine variations between how Mesa emulates the
> hardware and various hardware platforms actually work.
>
> So, who @Kitware do I need to talk to to get this patch back to
> mainstream?  I plan to file a bug on it, with code attached, tomorrow
> morning when I return to the office.  This is a little larger patch that I
> usually deal with (4 new files, extensive changes to a few others), so
> what's the preferred format for a patch this size?  I know there's a command
> with 'cvs diff' to get "patch"-style diffs, which seems the best option, but
> I always forget it...
>
>
> --
> Randall Hand
> Visualization Scientist,
> ERDC-MSRC Vicksburg, MS
> Homepage: http://www.yeraze.com
> _______________________________________________
> vtk-developers mailing list
> vtk-developers at vtk.org
>  http://www.vtk.org/mailman/listinfo/vtk-developers
>



--
Randall Hand
Visualization Scientist,
ERDC-MSRC Vicksburg, MS
Homepage: http://www.yeraze.com
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