Re: [AD] Hotplug joysticks

[Peter Wang <novalazy@xxxxxxxxxx>]

On 2010-08-18, Thomas Fjellstrom <tfjellstrom@xxxxxxxxxx> wrote:
> On August 18, 2010, Peter Wang wrote:
> > On 2010-08-18, Trent Gamblin <trent@xxxxxxxxxx> wrote:
> > > I've got joystick hotplugging working on Windows right now.
> > > This is one feature that maybe should be added to 4.9 now
> > > because it changes the semantics of how things work a bit.
> > > This is how it works:
> > > 
> > > The user installs joystick driver and calls al_get_num_joysticks and
> > > al_get_joystick(x). Everything behaves as normal until:
> > > The (new) system event source (al_get_system_event_source) emits a
> > > ALLEGRO_EVENT_JOYSTICK_CONFIGURED event.
> > 
> > I would prefer a dedicated joystick subsystem event source.  Actually,
> > we don't *need* a separate joystick event source per joystick, so maybe
> > we should use a single joystick event source for all joysticks.
> > In fact, the user doesn't need to see ALLEGRO_JOYSTICK objects at all:
> > just use the joystick number.  In many ways this would be more
> > convenient.
> 
> Thats what I thought too, but a user may want to have a separate thread per 
> display, and give the joystick to that thread as well. Unless this joystick 
> number can be used to register a given joystick in a separate queue?

No.  I can't see it being an important case to cater to, though.

> > > At this point, the user can ignore the event and proceed as
> > > normal, but if they call al_get_num_joysticks, the present "user"
> > > configuration of sticks changed to the present "system" view of
> > > joysticks (what is actually plugged in and not on the system at that
> > > time.) User calls al_get_joystick(x) again for all desired joysticks.
> > 
> > How about adding al_reinstall_joystick(), or al_reconfigure_joysticks()?
> > It would then be obvious that from that point, al_get_num_joysticks may
> > change, all old joystick structures become invalid (if that's what we
> > want), and they need to be reregistered (unless we switch to a single
> > joystick event source).

Another good thing is that this would support platforms without hotplug
notifications.  You could call al_reinstall_joystick() when the user
enters the "Controls" section of your game's menu, which could be more
efficient than al_uninstall_joystick + al_install_joystick.

> 
> I think it'd be better to just automatically de-register joysticks on 
> removal. In most cases all it means is the joystick events stop coming. if 
> you're doing anything clever with the ALLEGRO_JOYSTICK structures you're 
> asking for trouble. Though theres no need to free those structures either, 
> unless the joystick subsystem stores them in an array for some reason. But 
> either way there really isn't a need to do anything special with them.

I don't think it makes much difference if you unregister automatically,
except that the events which were waiting in queues would be removed.


Am I right that al_get_num_joysticks() will mean "max joystick number"
or "number of potential joysticks" (which it sort of does already)?
If you remove a joystick, the other joysticks ought to retain their numbers,
so there will be unused slots between between 0 .. al_get_num_joysticks()-1.

Peter