[PATCH wayland-protocols] Add the tablet protocol

[Daniel Stone]

Hi Jonas,

On 16 November 2015 at 11:59, Jonas Ådahl <jadahl at gmail.com> wrote:
> On Mon, Nov 16, 2015 at 11:21:36AM +0000, Daniel Stone wrote:
>> On 6 November 2015 at 04:24, Peter Hutterer <peter.hutterer at who-t.net> wrote:
>> > +    More than one tablet may exist, and device-specifics matter. Tablets are
>> > +    not represented by a single virtual device like wl_pointer. A client
>> > +    binds to the tablet manager object which is just a proxy object. From
>> > +    that, the client requests wp_tablet_manager.get_tablet_seat(wl_seat)
>> > +    and that returns the actual interface that has all the tablets. With
>> > +    this indirection, we can avoid merging wp_tablet into the actual wayland
>> > +    protocol, a long-term benefit.
>>
>> Yes, it turns out the wl_seat.get_* model was probably a pretty bad
>> anti-pattern. Oh well. To avoid too much object proliferation though,
>> how about something like:
>> <interface name="wp_tablet_manager">
>>   <request name="add_seat">
>>     <description summary="Add seat of interest">
>>       Add a seat of interest to this tablet manager. The client will
>> receive events for all tablets currently on this seat, as well as
>> tablets added to this seat in future.
>>     </description>
>>     <arg name="seat" type="object" interface="wl_seat"/>
>>   </request>
>>   [inline wp_tablet_seat here ...]
>> </interface>
>>
>> Then you can just bin wp_tablet_seat.
>>
>> Not a pattern we've previously employed, but I think it's a good one
>> that avoids one extra step of indirection, as well as making it a bit
>> easier for clients to do the right thing.
>
> How would it be easier for clients to do the right thing? It'd just make
> it easy to mix different seats' tools and tablets as there would be no
> more separation (except if one would bind a tablet manager per seat). Or
> should tools and tablets be considered on the same "super seat", i.e.
> would it be possible to see tool A from seat X on tablet V on seat Y?

It makes it easier, because right now we expect them to hold a
wp_tablet_manager, respond to new seats by creating a new
wp_tablet_seat, and having them respond to events on that as well. We
already make people hold absolute piles of objects, so one less seems
like it could be a good thing.

> Seems to me that making it possible to shove all seats in one pile is
> more error prone than having them clearly separated.

Possibly. I guess it depends on the failure mode. I can see it either way.

Cheers,
Daniel