[vtk-developers] Lightweight transform?

Thu Feb 6 17:41:38 EST 2003

Hi Chris,

When I modified the vtkTransform class back to add the Update() I made the
assumption that most people used a vtkTransform by building the transform
once and then applying it to a whole bunch of points (or uploading the
matrix to OpenGL via the actor from whence OpenGL would apply it).
I would be very interested to see a chunk of your code that demonstrates
how you are using the vtkTransform.

The 'Legacy Hack' warning occurs if you do something like this:
  transform->GetMatrix()->SetElement(i,j,val);
because you aren't allowed to directly change the transform's matrix
(for the same reason that you shouldn't directly change the vtkDataArray
inside a vtk data set that is part of a pipeline).

If the Identity(), Translate() etc. methods are too slow for your
application, you can subclass a new "vtkSimpleTransform" class
from the vtkLinearTransform class.

Regards,
 - David

-- 
  David Gobbi, MSc                dgobbi at imaging.robarts.ca
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario

On Thu, 6 Feb 2003, Volpe, Christopher R (Research) wrote:

> I have a need for a high-performance lightweight transform object, specifically, one that bypasses
> all of the Input and Concatenation stuff, and which has no need, therefore, for an Update call. I
> just want to be able to perform all the basic operations that vtkTransform provides (Rotate,
> Translate, etc), but as efficiently as possible. (We have an application that requires very high
> performance, and we've determined via Rational Quantify that an excessive amount of time is spent in
> some of the internal transform methods that get invoked from say, Identity(), and numerous others
> common methods.)
>
> At first I thought I'd subclass vtkTransform, but there are a number of methods in the whole
> transform hierarchy that are not declared virtual, and therefore overriding them is not possible,
> unless I also override the whole transitive-closure of upper-hierarchy methods that use them, which
> would make things inconvenient. So before I go cutting and pasting a Whole Lotta Code from various
> portions in the hierarchy into a new class, I thought I'd see if there's a simpler and more elegant
> approach available, perhaps some undocumented feature of sorts that could be harnessed. (I keep
> seeing references to some "Legacy Hack", but it's not clear to me if that's in any way relevant.)
>
> Thanks in advance for any insights.
>
> Chris
> > GE Global Research Center
> > ___________________________________________________________________________________________________
> > _______________________________________________
> >
> Dr. Christopher R. Volpe, Ph.D.
> Computer Scientist
> Visualization and Computer Vision Lab
> Imaging Technologies
> Bldg KW, Room C215
> P.O. Box 8, Schenectady, NY 12301
>
> (518) 387-7766, Dial Comm: 8*833-7766, Fax: (518) 387-6981
> e-mail: volpecr at research.ge.com    web: http://www.crd.ge.com/~volpecr
>
>
>
>
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