Re: [AD] event source casts

[Peter Wang <novalazy@xxxxxxxxxx>]

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);

and delete al_get_keyboard/al_get_mouse until such time that we need
them, if ever.

> > 2.  This change introduces some confusion about the `source' fields in
> > ALLEGRO_EVENTs.  If I have a display event will the event source field
> > point to the ALLEGRO_DISPLAY object, or the
> > al_get_display_event_source(display)?
> > 
> 
> True. What are the use-cases of the source field? In your specific
> example I think ALLEGRO_DISPLAY_EVENT itself needs another field
> "ALLEGRO_DISPLAY *display" which tells from which display the event
> originated.

Internally, the `source' field is now only used to delete events which
reside in queues when the event source is unregistered from the queue
(more commonly, destroyed).

The user also wants to know which who generated an event, and that would
be more convenient using the specific type of the event source (i.e.
ALLEGRO_DISPLAY, etc).  We can do as you say and add extra fields but I
think that is confusing.  At least we need to come up with new terms
for the two different kinds of "event sources".

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.

Peter