From: "Bernhard Glück" <jglueck@...>
Date: 2001-08-31T01:44:47+09:00
Subject: [ruby-talk:20587] Calling ruby methods from C++

Hi there!

I have been integrating Ruby into my game engine, and it works quite nicely, I can export my game objects to ruby classes which are then instantiated in scripts 
and can be modified very conveniently. Now I want to implement something the following way

I have a C++ base class called Object which represents a game object. Many classes are derived from it and are all exportet to the script so I can do for example 
the following in Ruby

m = Mesh.new()
m.Load( " test.x" )
m.Show()

which creates and displays a Mesh Object
( class Mesh: public Object in C++ by the way )

This all works very good and is stable.

Now my game engine is driven by messages e.g the Graphics Parts sends out a message "Collision" to two colliding objects which are then received by the C++ 
implementation and handeled. Now I want to send messages which the C++ Side cannot handle to the script ..
 I want to do the following being able to inherit from Exported C++ Classes( which works fine ) and implement additional methods for the object  in Ruby... Now 
when a message is not handeled by the C++ side it should call a method in the assosiacted ruby object (if an appropriate one exists ) Let me clarify with an 
example

Prerequisite Mesh is a class exported from my C++ part
AddToGame and Log are module methods from my engine, Log outputs a debug message
and AddToGame registers an object with the Game Manager so that it receives messages and everything.

In ruby:

class SpaceShip < Mesh 

	def OnDoSomething ( dummy )
	
		Log("Just a dummy log output")
	end

end

m = SpaceShip.new()
AddToGame( m )


Ok the C++ side of the Mesh ( or m as the instance ) does receive a "DoSomething" Message.. it can't handle it in C++ so it sends it too the m script object
in which the OnDoSomething method should be called to handle it ...

But I cant seem to get that working !!!

When Mesh is exported from C++ it is with the following code: 
(ObjectPtr is a smartpointer by the way ,and the following code is a macro for easy exporting of Object derived classes..(cname is a macro parameter the real class 
name ) 
Of particular interest should be the  obj->linkScriptClass call where the self VALUE is stored.... shouldn't the self VALUE be a handle to the SpaceShip class 
instance when used in the code above ?

		static VALUE cname##New( VALUE self ) \
		{ \
			ObjectPtr * inst = new ObjectPtr(); \
			*inst = Factory()->CreateObject(#cname); \
			VALUE t = Data_Wrap_Struct(self,0,SE_DELETE(cname##Delete),inst); \
			rb_obj_call_init(t, 0, NULL); \
			Object * obj = inst->Get(); \
			obj->LinkScriptClass( self ); \
			return t; \
		} \
 

And when I try to call the SpaceShip method it crashes all the time, I am doing so
		
		In the upper cases m_msg contains "DoSomething"
		and val is the VALUE stored in the above procedure ( the C++ Ruby "Constructor" )

		String callString = "On";
		callString += m_msg;
		
		// Generated for the method
		ID callId = rb_intern( callString );

		// Now create the parameter array for the call...
		Array<VALUE> args;

		// And make the script call
		rb_funcall2_protect( val,callId,args.Size(),args.Begin() );


Any idea how to achieve what I want ?
Thanks in advance
Bernhard Gl�ck