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NodeData based classic plugin classes can implement NodeData::GetDParameter(). This allows to define the values of parameters accessed with C4DAtom::GetParameter(). This is done to handle data that is not stored in the object's BaseContainer. It is also used to create parameters that depend on the value of other parameters or element properties.

NodeData::GetDParameter() corresponds to C4DAtom::GetParameter().

Note: In most cases, when implementing NodeData::GetDParameter(), one will also need to implement NodeData::SetDParameter(). For example, if the value is stored in a member variable.

Usage

NodeData::GetDParameter() is called when the value of a parameter is accessed with C4DAtom::GetParameter(). It is possible to define or change the returned value.

  Bool GetDParameter(GeListNode* node, const DescID& id, GeData& t_data, DESCFLAGS_GET& flags)
  {
    if (node == nullptr)
      return false;
    // check parameter ID
    switch (id[0].id)
    {
      // This parameter is not stored in the BaseContainer
      case EXAMPLE_GENERATOR_PARAMETER_NOT_BC:
      {
        // set the value from a member variable
        t_data.SetInt32(_value);
        // Parameter retrieved.
        flags |= DESCFLAGS_GET::PARAM_GET;
        return true;
      }
    }
    return SUPER::GetDParameter(node, id, t_data, flags);
  }

Note: Such member variables must also be handled in NodeData::Read(), NodeData::Write(), NodeData::CopyTo() and NodeData::SetDParameter().

The arguments of the function are:

The node itself.
The parameter DescID in question.
A GeData object to return the read parameter value.
These flags:
- DESCFLAGS_GET::PARAM_GET : Parameter retrieved.
- DESCFLAGS_GET::NO_GEDATADEFAULTVALUE : If set, the GeData default type will not be initialized for C4DAtom::GetParameter.

Certain cases have to be handled with special functions:

The macro HandleDescGetVector has to be used to handle vector parameter values.
In nodes with a material preview description GetDParameterPreview() can be used.

Further Examples

  // This example of a TagData plugin defines the value of the
  // Tag's parameter by calculating the volume of the host object.
  Bool GetDParameter(GeListNode* node, const DescID& id, GeData& t_data, DESCFLAGS_GET& flags)
  {
    if (node == nullptr)
      return false;
    // check parameter ID
    switch (id[0].id)
    {
      case EXAMPLE_TAG_VOLUME:
      {
        Float  volume = 0.0;
        GeData data;
        BaseTag* const tag = static_cast<BaseTag*>(node);
        if (tag != nullptr)
        {
          BaseObject* const hostObject = tag->GetObject();
          if (hostObject != nullptr)
          {
            // check the object type
            switch (hostObject->GetType())
            {
              // calculate volume of sphere primitive
              case Osphere:
              {
                hostObject->GetParameter(PRIM_SPHERE_RAD, data, DESCFLAGS_GET::NONE);
                const Float radius = data.GetFloat();
                volume = (4.0 / 3.0) * maxon::PI * radius * radius * radius;
                break;
              }
              // calculate volume of cylinder primitive
              case Ocylinder:
              {
                hostObject->GetParameter(PRIM_CYLINDER_RADIUS, data, DESCFLAGS_GET::NONE);
                const Float radius = data.GetFloat();
                hostObject->GetParameter(PRIM_CYLINDER_HEIGHT, data, DESCFLAGS_GET::NONE);
                const Float height = data.GetFloat();
                volume = maxon::PI * radius * radius * height;
                break;
              }
              // etc.
              default: break;
            }
          }
        }
        t_data.SetFloat(volume);
        flags |= DESCFLAGS_GET::PARAM_GET;  // don't forget to set this flag
        return true;
      }
    }
    return SUPER::GetDParameter(node, id, t_data, flags);
  }

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