Now that we have the tag, let's cover the basic data pipeline, which is implemented using the vtkAlgorithm class. This class provides input and output ports. Output ports are accessible via GetOuptutPort member functions, which return a proxy object ( vtkAlgorithmOutput *) for an actual output port.

In Dataflow concepts, vtkAlgorithmOutput can be made a producer Port - it corresponds to a single data output point. We support it as such by defining a PortTraits type, and associating it with vtkAlgorithmOutput:

namespace boost { namespace dataflow { namespace vtk {

// PortTraits for vtkAlgorithmOutput objects, which produce data.
// We specify the PortCategory (ports::producer) and Tag (vtk::tag).

struct vtk_algorithm_output_producer
    : public port_traits<ports::producer, vtk::tag> {};
    
} } } // namespace boost::dataflow::vtk

// This macro specializes the traits_of template to the specified
// PortTraits, and also verifies that the PortTraits requirements are satisfied.
// The traits_of template is used by the Dataflow library to associate
// a Port with its PortTraits.
DATAFLOW_TRAITS(vtkAlgorithmOutput, vtk::vtk_algorithm_output_producer)

Now that we have a producer Port, we need a consumer Port. vtkAlgorithm can accept incoming connections using the AddInputConnection and SetInputConnection member functions. Since we will make vtkAlgorithm a Component, we can't make it a Port directly - but we can use the port_adapter class to refer to the Port functionality of vtkAlgorithm, so we set up a PortTraits class to represent this Port functionality:

namespace boost { namespace dataflow { namespace vtk {

struct vtk_algorithm_consumer
    : public complemented_port_traits<ports::consumer, vtkAlgorithmOutput, vtk::tag> {};
    
typedef port_adapter<vtkAlgorithm, vtk::vtk_algorithm_consumer, vtk::tag>
    vtk_algorithm_consumer_adapter;
    
} } } // namespace boost::dataflow::vtk

Note that for the consumer traits, we inherited complemented_port_traits rather than port_traits. In doing so, we made vtk_algorithm_consumer a ComplementedPortTraits. This basically states that any Port with vtk_algorithm_consumer traits is intended for connections with vtkAlgorithmOutput Ports. This piece of information can make things easier for the Dataflow library in certain cases (e.g., the prototype Dataflow.Blueprint layer currently only knows how to connect two blueprint ports if at least one of them is a ComplementedPort).

Next

Making things Connectable