[vtk-developers] vtk perf - issue 2 - transformations

[Mark Beall]

I think this is an easy one.

In our application, the transformation for an actor is almost always
an identity. By adding a flag into vtkMatrix4x4 that keeps track of
whether it is an identity (it would be set when vtkMatrix4x4::Identity
is called and unset whenever anything that changes the matrix is
called), the calls to push the transformation matrix can be
skipped for identity transformations.
One potential gotcha is that vtkMatrix4x4::Element is public,
so it's possible that there are things external to vtkMatrix4x4 that 
directly manipulate this matrix which would cause this to be 
inconsistent.

mark