Re: [AD] event source casts

[Peter Wang <novalazy@xxxxxxxxxx>]

On 2009-08-04, Elias Pschernig <elias.pschernig@xxxxxxxxxx> wrote:
> On Tue, 2009-08-04 at 11:07 +1000, Peter Wang wrote:
> > On 2009-08-03, Elias Pschernig <elias.pschernig@xxxxxxxxxx> wrote:
> > > On Tue, 2009-08-04 at 00:20 +1000, Peter Wang wrote:
> > > > 
> > > > A couple of comments.
> > > > 
> > > > 1.  al_register_event_source(queue,
> > > > 	al_get_keyboard_event_source(al_get_keyboard()));
> > > > 
> > > > is a bit silly since al_get_keyboard() has no other use any more.
> > > > Same with al_get_mouse().
> > > 
> > > As before with the cast.
> > 
> > I was thinking we'd have:
> > 
> >     ALLEGRO_EVENT_SOURCE *al_get_keyboard_event_source(void);
> >     ALLEGRO_EVENT_SOURCE *al_get_mouse_event_source(void);
> 
> Makes sense. (Support for multiple mice could be a reason to re-publish
> ALLEGRO_MOUSE at some point I guess.)

I'll let you take care of it.

> > So I still would like to guarantee that
> > 
> >     display == al_get_display_event_source(display);
> > 
> > and so on, as we had before ALLEGRO_STREAM and user event sources came
> > along.
> >
> > The idea that I had during one of the Hack Days was, I believe, to make
> > ALLEGRO_EVENT_SOURCE a structure with a publically known size but
> > private fields.  Then users can derive their own event sources in the
> > same way as the core library without the extra indirection.
> > 
> >     struct MY_THING {
> > 	ALLEGRO_EVENT_SOURCE es;
> > 	int my_field;
> > 	...
> >     };
> > 
> > I came across some minor problem when implementing it at that time, but
> > really I think there should be no problem so I'll give it another go.
> > 
> 
> Sounds good. In my case, it will look like this though:
> 
> struct MY_THING {
> 	MY_OBJECT super;
> 	ALLEGRO_EVENT_SOURCE es;
> }
> 
> So the assumption about the pointer values being the same still would
> not hold - it shouldn't matter at all though, but we simply can't
> enforce it for addons or even suggest to them that it's a good idea.

Ok, I've committed my change.

In your case you can still easily get from the event source pointer to a
MY_THING pointer by subtracting the offset of the es field ;)  Could be
handy.

Peter

PS. r12345