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

[Fauze Polpeta]

Thanks for your support David and sorry for the cross-post...I was wondering
if one could image some core-based solution.

In our case a medical application is being prototyped and the ray-cast
volume was preferred for volumetric reconstruction. The point is that our
application is connected to a device that tracks surgical instruments that
are represented by polydata. So, theoretically, we can't abdicate of the
ray-casting while moving these tools during a given surgical procedure. This
is the reason I mentioned if it is possible to bypass the pipeline
processing in order to render this polydata using pure OpenGL commands.

Thanks again

Regards

Fauze



On Fri, Jan 22, 2010 at 7:04 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> 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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