Gamepad focus model (Re: Input and games.)

[Daniel Stone]

Hi,

On 14 May 2013 05:49, Rick Yorgason <rick at firefang.com> wrote:
> Okay, so the most common configuration would be one seat with a mouse,
> keyboard, and gamepad. If you only ever play single player games, this is
> all you would see.
>
> When you have multiplayer games, you just want to be able to launch the game
> and have everybody automatically in it. You don't want your extra players to
> have to think about focusing the app or anything like that.

Yes, 100%.

> That's the crux of the problem: how do you have one focus for multiple
> players? The many-gamepads-per-seat model solves this, but it has a couple
> problems:
>
> 1) Some compositors may put every gamepad in one seat, and some compositors
> may assign one gamepad per seat. The game programmer has to support both
> code paths. And unfortunately, when game programmers inevitably neglect to
> do that, the gamers are going to blame the compositors rather than the
> games. Wayland will get a reputation as a display server where you have to
> configure your gamepads differently for different games.

Compositors can implement maximise badly too, or multi-display
support.  But it's not an argument to push the complexity out.  It's
an argument for not running broken compositors.

> 2) Gamepads aren't the only scenario where you want to have one focus for
> multiple players.
>
> Here's a couple scenarios that are complicated by breaking the seat == user
> model:

It's not seat == user, it's seat == focus.

> A) You're playing split-screen Halo. Two users have a mouse/keyboard, and
> two users have gamepads.
>
> In the seat == user world, we know how this is set up: seat 1 has a
> mouse/keyboard, seat 2 has a mouse/keyboard, seat 3 has a gamepad, and seat
> 4 has a gamepad.

We know how it's set up, but we don't know how it works.  How does the
compositor know to focus 3 and 4 at Halo, rather than at the browser
or whatever else is running at the time? You can't have the keyboard
and mouse tell you, because they're different seats.  So it's just
manual then? Or the compositor making random guesses?

> In the many-gamepads-per-seat model, I don't know how to set this up. The
> first two players would have to have their own seats, but since the player
> ID is in the gamepad, where do we get their player numbers from? And what
> about players 3 and 4? Where do their gamepads go? They can go in seat 1,
> but then how do you distinguish player 1 from players 3 and 4? And why does
> player 2 have to manually focus the game?

The gamepads go to whichever seat it is that's directing their focus.
If their focus is entirely manually set, then they go in their own
seat.  Simple, no? Or am I totally missing something, and do gamepads
under Wayland typically not follow keyboard/mouse focii? (I don't mean
in really contrived theoretical cases, I mean in the overwhelming
majority of situations.)

> (I don't believe this scenario is inherently exotic. Lemmings, Settlers, and
> Hired Guns all did this back in the DOS and Amiga days, before OSs made it
> harder to distinguish mice from each other.)

Yes, that's the tradeoff you get for multitasking, and having the OS
know where your mice are, rather than having to tell every single game
where every single mouse is.

> B) Imagine that, with the current trend of adding touchpads to gamepads,
> Fruit Ninja releases a multi-player version. All players play on the same
> "field", but it tracks their scores independently; whomever slashes the
> fruit first gets the points. Let's imagine we have player 1 with a separate
> touchpad, and players 2 and 3 with gamepads that have touchpads built in.
>
> In the seat == user model, it's obvious how this should be set up: seat 1
> gets a touchpad, seat 2 gets a gamepad with the associated touchpad, and so
> does seat 3.
>
> In the many-gamepads-per-seat model, the question rises again of where you
> put the gamepads. Do they go in the same seat as the touchpad they're
> attached to? Or do they all end up in seat 1? If they're all in seat 1, does
> the player indicator on their controller match up with their actual player
> number? And again, they all have to individually focus the game.

Again, how does the focus get changed? Where are the gamepads deriving
their focus from? Put them in that seat, and add a wl_touch object for
every gamepad.

>> If the focus can be changed independently, how does this happen?
>
> Focus can only be changed independently for "collaborative" seats.
> "Collaborative mode" means "I want to interact with the desktop
> independently." When collaborative mode is turned off, your focus is derived
> from a seat which *is* in collaborative mode.

OK, so what's the downside from having the gamepad embedded inside the
seat it derives its focus from?

>> If
>> the keyboard/pointer seat switches focus to another game, do both
>> seats switch, or does the other stay behind?
>
> Assuming seat 2 is following seat 1, they both switch.
>
>> If both switch - why are
>> we complicating the focus model rather than just adding both to a
>> seat?
>
> Because this problem doesn't start and end with gamepads. If we take the
> multiple-gamepads-per-seat model to its logical conclusion, then to support
> the scenarios above, you would also need multiple mice/keyboards/touchpads
> per seat. And then how do you determine which devices belong to which players?

No, we don't because we don't lose information by aggregating them.
If you want to support multiple independent mice, then the expectation
is that the mice can keep on going straight out of the window, and
then change the focus.  So either it changes the focus for everyone
(same seat), or for just it (separate seat).

If you want relative mice, Kristian's relative work should probably be
extended to provide one object per device, similar to wl_gamepad,
since aggregating it becomes a lot less useful.

But if it doesn't have any involvement or interaction with the core
shell UI, then why is it a seat? A seat has a pretty singular meaning
right now, and I'd rather not complicate and change that for all
clients, and make them contort themselves in order to support a fairly
niche usecase.

Maybe I'm just being thick, but I honestly can't see the downsides of
the multiple-gamepads-per-seat model.  One seat is currently
restricted to one of each device, but that's only because we were able
to aggregate those devices without losing information.  For gamepads,
that's blatantly not true, but they don't have interactions with the
shell and core UI - that's driven by the other devices in the seat, or
by the shell's own policy - so the usual answer of 'put them in
another seat' doesn't apply I think.

>> The wl_seat == one player idea is a nice little mental model, but it's
>> not in any way worth complicating our core input/focus management
>> model for.
>
> I believe we're both trying to avoid complication :)

:)

Cheers,
Daniel