General Transforms, anyone?

David Gobbi dgobbi at
Thu Dec 16 16:07:10 EST 1999

Hi Will,

Thanks for the feedback, and thanks to the others who have gotten
back to me on this.

I don't think that virtual function overhead will be much of 
a problem -- even very simple transforms (i.e. 4x4 matrix) are
expensive enough that the virtual function overhead should be
minimal.  A little benching will be necessary...

Backwards compatibility will be essential.  Personally, I would
love to re-write vtkTransform from the ground up to use a
quaternion/4x4-matrix hybrid, make vtkNormals use 4 points instead
of three, but I'm willing to compromise ;)

I probably won't have anything ready to send out until the new
year, but I'll refresh the discussion then.

 - David

  David Gobbi, MSc                    dgobbi at
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario

On Thu, 16 Dec 1999, Will Schroeder wrote:

> Hi David-
> At 11:26 AM 12/16/99 -0500, you wrote:
> >Hi All,
> >
> >I'd like to hear what people think about the idea of a 
> >'general transform,' i.e. a base class with the following
> >methods:
> This idea is promising, at least from what I understand. My major concern
> is performance, and backward compatibility. Performance would be
> affected depending on which methods were made virtual  (if any) - that
> could be an issue. It looks like backward compatibility could be
> preserved. Also, several other people have requested other types of
> transformations, and this would fit right in.
> I think what is preventing action at this point is that we all feel
> that additional discussion (and more details) are required. I would
> suggest the following - create a complete .h file for
> vtkGeneralTransform - and send it around. Then we can all look and
> follow up with comments. At some point interested parties can fork from
> vtkusers.
> Will
> --------------------------------
> Dr. William J. Schroeder
> Kitware Visualization Solutions / vtk Commercial Support
> 469 Clifton Corporate Parkway
> Clifton Park, NY 12065
> will.schroeder at
> 1-518-371-3971 (Phone & Fax)

This is the private VTK discussion list.  Please keep messages on-topic.
Check the FAQ at: <>
To UNSUBSCRIBE, send message body containing "unsubscribe vtkusers" to
<majordomo at>.  For help, send message body containing
"info vtkusers" to the same address.     Live long and prosper.

More information about the vtkusers mailing list