4.8.2 Attaching User Objects to CS Objects

This section explains how you can assign your own game specific data to Crystal Space objects (i.e. like meshes and sectors). In this section we explain how to do it from within code. In the next howto (see section Attaching User Objects to CS Objects in a map file) we explain how you can do this from a map file.

The Crystal Space Object System

Almost all objects in the Crystal Space engine implement the iObject interface. Because of this you can attach your own objects to them. This can be very useful to attach game specific data to Crystal Space objects. For example, you may want to attach the state of an actor to the mesh object representing that actor (like current amount of ammunition, health, ...).

Defining Game Data

To define data that you can attach to any other Crystal Space object (or any object implementing iObject) you also have to create an object that implements iObject. The easiest way to do that is to inherit from csObject which implements iObject for you. Here is an example on how you can do this easily:

class MyOwnData : public scfImplementationExt1<MyOwnData, csObject,
	scfFakeInterface<MyOwnData> >
{
private:
  int myDataInt;

public:
  SCF_INTERFACE (MyOwnData, 1, 0, 0);
  ...
  MyOwnData () : scfImplementationType (this)
  {
    ...
  }
  virtual ~MyOwnData ()
  {
    ...
  }
  
  ...
  
  int GetMyData () const { return myDataInt; }
  void SetMyData (int newData) { myDataInt = newData; }
};

In this example you must use some SCF templates so that your own class becomes a valid SCF object that inherits from csObject properly.

Basically you create a class called `MyOwnData' which inherits from csObject. In that class you can do whatever you want with respect to your own game data. In the example above we only have a variable `myDataInt' but of course you can do whatever you want. The SCF templates make sure that you can later query for that object (using scfQueryInterface for example).

Attaching Game Data

To attach your own data to some Crystal Space object you can use iObject::ObjAdd(). The example below shows how you can attach an instance of MyOwnData to a mesh:

csRef<MyOwnData> mydata; mydata.AttachNew (new MyOwnData ());
mydata->SetMyData (...);
iMeshWrapper* mesh = ...;
mesh->QueryObject ()->ObjAdd (mydata);

mesh->QueryObject() is interesting. Many Crystal Space objects that implement iObject have a convenience function called QueryObject() which will return a reference to the iObject implementation. This code is equivalent to:

csRef<iObject> obj = scfQueryInterface<iObject> (mesh);

with the important difference that QueryObject() does not increment the reference count. If an object doesn't have this convenience function you must use scfQueryInterface instead.

Finding Game Data

To find if some object has your data attached to it you can use the following code:

csRef<MyOwnData> mydata =
  CS_GET_CHILD_OBJECT(mesh->QueryObject(), MyOwnData);
if (mydata)
{
  ... (use mydata)
}

Removing Game Data

To remove your data you can use:

csRef<MyOwnData> mydata =
  CS_GET_CHILD_OBJECT(mesh->QueryObject(), MyOwnData);
if (mydata)
{
  mesh->QueryObject ()->ObjRemove (mydata);
}

Include Files

The include files useful for this section are:

#include <iutil/object.h>
#include <csutil/csobject.h>

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