Marshalling Hints#


VTK auto generates (de)serialization code in C++ for classes annotated by the VTK_MARSHALAUTO wrapping hint.

On the other hand, the VTK_MARSHALMANUAL macro is used to indicate that a class will take part in marshalling, but it cannot trivially (de)serialize it’s properties. This is because one or more of the class’s properties may not have an appropriate setter/getter function that is recognized by the VTK property parser.

For such classes, a developer is expected to provide the code to serialize and deserialize the class in vtkClassNameSerDes.cxx. This file must satisfy three conditions:

  1. It must live in the same module as vtkClassName.

  2. It must export a function int RegisterHandlers_vtkClassNameSerDesHelper(void*, void*) with C linkage.

  3. It must define and declare these three C++ functions:

    1. A serializer function

      nlohmann:json Serialize_vtkClassName(vtkObjectBase*, vtkSerializer*)
    2. A deserializer function

      void Deserialize_vtkClassName(const nlohmann::json&, vtkObjectBase*, vtkDeserializer*)
    3. A registrar function

      int RegisterHandlers_vtkClassNameSerDesHelper(void* ser, void* deser)

      that registers:

      • a serializer function with a serializer instance

      • a deserializer function with a deserializer instance

      • a constructor of the VTK class with a deserializer instance


Excluding properties#

You can exclude certain properties of a class by simply annotating the relevant setter/getter functions with VTK_MARSHALEXCLUDE(reason), where reason is one of VTK_MARSHAL_EXCLUDE_REASON_IS_INTERNAL or VTK_MARSHAL_EXCLUDE_REASON_NOT_SUPPORTED. This reason will be printed in the generated C++ source code explaining why the property was not serialized.

Custom get/set functions#

Some properties may not be correctly recognized by the property parser because they have different names for their get and set functions. You can override this by annotating the get function with the VTK_MARSHALGETTER(property) macro. Doing so will ensure that the function gets recognized as a getter for property. VTK_MARSHALSETTER(property) serves a similar purpose.