[vtkusers] Volume Rendering and Large Textures

[Lisa Sobierajski Avila]

Hello Sean,

The volume rendering texture mapping supported in VTK right now is based on 
2D texture mapping. There is a target texture size (default of 512x512) - 
if the two minor-direction dimensions of the volume are smaller than this 
(256 or less) then multiple slices will be packed into one texture. If the 
minor-direction dimensions are bigger than this, then the target texture 
size will be increased to fit one slice of the volume and still be a power 
of 2, with one slice rendered at a time. There are not three copies of the 
volume - this is all computed on the fly every render. It would be faster 
to store 3 copies of the volume in RGBA format - but only if no shading is 
occurring - otherwise we still need to traverse the volume to compute 
shading. Right now if you try to load a volume with dimensions larger than 
you can have a 2D texture (maybe a 1024x1024x20 volume with a video card 
that can only support 512x512 textures) you are out of luck. Most 
reasonable video cards support 2048x2048 I think, even if it doesn't all 
fit in memory at once, so I have never encountered this problem. (Although 
I have encountered the problem where the rendering gets very slow because 
the software driver is averaging the texture down to fit in the available 
memory - but this was an old video card)

Hope that comes close to answering your question.


Lisa

At 12:09 PM 8/22/2000, Sean Spicer wrote:

>All,
>
>Can someone explain to me VTK's strategy for handling texture-map Based
>volume-rendering (e.g. vtkVolumeTextureMapper2D - I think) when the
>specified volume does not fit entirely into texture memory?  I understand
>that 3 copies of the volume must be made for 2D decomposition of the
>volume, but what happens when texture-memory is over subscribed - multiple
>brick volumes.  Can the standard routines in VTK handle this easily?
>
>Thanks,
>
>sean
>
>___________________________________________________________________________
>Sean Spicer                       Stanford University Medical Center
>Biomechanical Engineering         Division of Vascular Surgery, Suite H3642
>Cardiovascular Biomechanics Lab   Stanford CA, 94305
>                                   Telephone...650.723.1695
>                                   Fax.........650.723.8762
>
>              http://solvedeath.stanford.edu/~spicer
>
>
>
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