[vtkusers] Help on VTK's Performance: Volume Rendering + Polygonal Object Moving

[David Gobbi]

Hi Fauze,

Please don't cross-post to the vtk-developers list, since that list is
only for developer issues.

Mixing polygonal objects with software ray-cast volume rendering is an
expensive process, it involves reading a partially rendered scene from
the video card back to main memory and re-doing the volume rendering
using the information in the depth buffer.  Every time the object
moves, the ray-cast has to be redone.

If you need fast volume rendering intermixed with polydata, you should
use vtkVolumeTextureMapper3D or vtkVolumeTextureMapper2D.  These
volume mappers do all of the polydata/volume intermixing right on the
graphics cards.

What I often do is use a vtkLODProp3D so that I can use the texture
volume rendering when I'm dragging things, but have it automatically
switch to ray-casting when I stop dragging the mouse.

  David


On Fri, Jan 22, 2010 at 1:33 PM, Fauze Polpeta <fauze.polpeta at gmail.com> wrote:
> Dear VTK Users;
> I have worked on a project that requires a Polygonal Object ( or at least a
> simple Line ) to be moved on the fly on a volume rendered scene built on top
> of a vtkVolumeRayCastMapper abstraction.
> This goal was successfully reached but we have faced a drastic performance
> degradation when moving the polygonal object into/across the volume scene.
> We have assumed this is a consequence of the VTK's pipeline  processing
> model. If anyone confirm that, we would like to ask any help in the sense of
> pointing any strategy for achieving any (minimal) performance improvement.
> Perhaps, getting the OpenGL Context and rendering our polygonal object using
> OpenGL commands; thus skipping the VTK's pipeline processing. Is this
> feasible?
> Thanks in advance for any help.
> Regards,
> Fauze
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