[vtk-developers] Unstructured Volume Rendering Mesa support

[Lisa Avila]

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>http://www.yeraze.com
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