[Paraview-developers] How to implement an identity filter ?

[houssen]

How to write an identity filter ? (1 input port, 1 output port, output 
= input whatever input may be)

I need to write a custom filter. I am used to VTK "from outside" 
(creating/handling vtk pipelines/scene/object from a main program) that 
is basically without the need to understand all internal VTK mechanics 
(except the SetInputConnection concept). I am not yet used to VTK 
internal mechanics that is necessary for writing a ParaView plugin.

I need my filter to do "complex" stuffs. As I couldn't make it work, I 
simplified as much as possible to obtain finally an identity filter (!) 
: this is still not working. I feel I still miss something from VTK 
internal mechanics.

As far as I understand, in the constructor, I need :
myFilter::myFilter () { SetNumberOfInputPorts  ( 1 ); 
SetNumberOfOutputPorts ( 1 ); }

So then I need to implement the FillXXXPortInformation :
int myFilter::FillInputPortInformation ( int vtkNotUsed ( iPort ), 
vtkInformation * ipInfo )
{
   if ( ipInfo ) ipInfo -> Set ( vtkAlgorithm::INPUT_REQUIRED_DATA_TYPE 
(), "vtkDataObject" ); // Filter allowed data types
   return 1;
}
int myFilter::FillOutputPortInformation ( int vtkNotUsed ( iPort ), 
vtkInformation * ipInfo )
{
   if ( ipInfo ) ipInfo -> Set ( vtkDataObject::DATA_TYPE_NAME (), 
"vtkDataObject" ); // Output data type to be created
   return 1;
}

So, now I only need to implement the ProcessRequest gateway:
int myFilter::ProcessRequest ( vtkInformation * ipRequest, 
vtkInformationVector ** ipInputVector, vtkInformationVector * 
opOutputVector )
{
   if ( ipRequest && ipRequest -> Has ( 
vtkDemandDrivenPipeline::REQUEST_DATA () ) )
     if ( ipInputVector && opOutputVector ) opOutputVector = 
ipInputVector[0];
    return Superclass::ProcessRequest ( ipRequest, ipInputVector, 
opOutputVector );
}

I believed that I would be the only steps to proceed to get an identity 
filter. When I use my identity filter in Paraview, I get errors like :
ERROR: In 
/.../ParaView-v4.3.1-source/VTK/Common/ExecutionModel/vtkDemandDrivenPipeline.cxx, 
line 810
vtkPVPostFilterExecutive : Input for connection index 0 on input port 
index 0 for algorithm vtkPVPostFilter(0x16d0ec0) is of type 
vtkDataObject, but a vtkPolyData is required.

Some logic is still missing here : could somebody explain me what and 
why ?

Thanks,

Franck