[Gambas-devel] A few comment about Tommy's changes

[Benoît Minisini]

> Benoit,
> Thanks for correcting my errors.
> I'm working on point 1 and 4, it's not so difficult, but if you could
> explain me why shouldn't I use pointer (point 2) if it works, and what to
> use instead? The same with point 3, as I wrote some time ago, I'm not a
> good C programmer, I'm still learning. And after I clean up my code, I
> promise not to mess anymore ;)
> 
> Tomek.
> 

Pointer can points at any memory address. By assuming that they are pointing 
to a GluQuadric, you can make crash the interpreter, or worse make it doing 
random things just by using a random pointer. THIS IS BAD!

Let's take GluQuadric as an example:

1) You must create a Gambas class to manage it. Let's keep the same name, 
GluQuadric.

2) Look at the source code of the 'Rect' class, and use it as a template.

'Rect' is defined in /trunk/main/lib/draw/crect.c and 
/trunk/main/lib/draw/crect.h.

So you should create a 'cgluquadric.c' and a 'cgluquadric.h' file. I added a 
"c" in front of the file name to remember that these files implement a Gambas 
class.

3) The Gambas GluQuadric object is defined by a C structure that always starts 
with a GB_BASE field. All Gambas objects are structure that begins with that 
structure. GB_BASE includes a pointer to the object class and the object 
reference count.

	typedef
	  struct {
	    GB_BASE ob;
	    GluQuadric *quadric;
	  }
	  CGLUQUADRIC;

4) Contrary to the 'Rect' class, you cannot create a 'GluQuadric' from scratch 
(afaik). So you must add the GB_NOT_CREATABLE() keyword in the GB_DESC class 
description.

	GB_DESC GluQuadricDesc[] = 
	{
	  GB_DECLARE("GluQuadric", sizeof(CRECT)), 
	  GB_NOT_CREATABLE(),

	  // No _new method is needed I think

	  ...
	  GB_END_DECLARE
	};

5) But you will add a public C function in the gluquadric.c file that will 
create a GluQuadric Gambas object from a 'GluQuadric *' C pointer, as returned 
by the 'gluNewQuadric' OpenGL function.

	CGLUQUADRIC *GLUQUADRIC_create(GluQuadric *quadric)
	{
	  CGLUQUADRIC *ob = GB.New(GB.FindClass("GluQuadric"), NULL, NULL);
	  ob->quadric = quadric;
	  return ob;
	}

6) Then you will implement GLUNEWQUADRIC that way:

	#include "cgluquadric.h"

	BEGIN_METHOD_VOID(GLUNEWQUADRIC)

	  CGLUQUADRIC *ob = GLUQUADRIC_create(gluNewQuadric());
	  GB.ReturnObject(ob);
		
	END_METHOD

7) And you will declare it that way:

	GB_METHOD("NewQuadric", "GluQuadric", GLUNEWQUADRIC, NULL),

8) All other functions using GluQuadric must be modified, so that instead of 
taking a pointer, they take a GluQuadric Gambas object.

Then the pointer you will receive in the function will be either NULL, either 
a pointer to a CGLUQUADRIC structure.