[vtkusers] new pipeline execution: REQUEST_UPDATE_EXTENT

[Jens]

Dear vtk-user
I have created a class "myData" which inherits from 
"vtkUnstructuredGridAlgorithmn" and therefor uses the new pipline execution 
of vtk 5.0, but I need to know how to react on a "REQUEST_UPDATE_EXTENT" send 
because of a change of the active cell attribute:

If I want to change the visible cell-attribute after the first render I call
void changeAttribute(const char* attName)
{ 
	mydata->GetOutput()->GetCellData()->SetActiveScalars(attName);
	ren->Render();
}

That calls
vtkUnstrukturedGridAlgoithmn::ProcessRequest(vtkInformation* request, ...)
{.....
	return this->RequestUpdateExtend(...)
}
which ends up in a function of myData: 

myData::RequestUpdateExtend(
	vtkInformation* request, 
	vtkInformationVector**,
	vtkInformationVector*)
{
	???????
}

What do I have to do that the new active cell attribute gets rendered but the 
unstructured grid stays the same (no reload) ?
What else do I have to check on an REQUEST_UPDATE_EXTENT? (active point 
attributes (scalar/vektor) etc. )

	Greetings
		Jens