[vtkusers] accessing/poping transforms in vtkGeneralTransform

[David Gobbi]

On 9 Apr 2001, Alexandre Guimond wrote:

> Hi.  I have a vtkGeneralTransform object.  I can add transformations
> to it using Concatenate().  I was wondering if there is a way to
> access the elements in the concatenation?  

Get a recent version of vtkGeneralTransform from CVS.

> Also, is there a way to remove transformations
> that I add using concatenate?  There are Push() and Pop() functions,
> but they don't take or return arguments.  Can someone explain me what
> they do?  thx

The Push() and Pop() are in there for backwards compatibility with the
original vtkTransform class, and have nothing to do with transform
concatenation.  I've considered removing them from vtkGeneralTransform.

The only way to remove transformations from a vtkGeneralTransform is
to call the Identity() method and then build up the transform again
from scratch.  An exception to this is the Input of the transform:
The vtkGeneralTransform is structured roughly like so:

<PreMultiply Concat'd xforms>*<Input>*<PostMultiply Concat'ed xforms>

where the the Input is treated as identity if it is NULL.  When
Identity() is called on the transform, all the Pre and Post transforms
are stripped off leaving just the Input transform.

 - David