wl_tablet specification draft

[Pekka Paalanen]

On Sun, 29 Jun 2014 23:43:21 -0700
Bill Spitzak <spitzak at gmail.com> wrote:

> On 06/29/2014 11:33 PM, Pekka Paalanen wrote:
> 
> >> moving the visible cursor doesn't necessarily mean that it must translate
> >> into the wl_pointer protocol. It's probably awkward at first if the pointer
> >> moves and clients don't react to it but if we essentially require the
> >> toolkits to support wl_tablet then this will go away quickly.
> >
> > I suspect it will be very hairy to make that work. Clients always set
> > the pointer cursor image when the pointer enters a surface. If you move
> > the cursor without using wl_pointer protocol, what happens with the
> > cursor image?
> 
> I was assuming the enter event contains enough information to know which 
> device is causing it.

It is the wl_pointer of a specific wl_seat:
http://people.collabora.com/~jonny/protocol/wl_pointer.html#Event:enter

No information about the actual physical device at all.

> If not it needs to be extended to contain all the 
> information that is in a "move" event.

It already contains more information than motion:
http://people.collabora.com/~jonny/protocol/wl_pointer.html#Event:motion

No, we are not adding physical device identification to wl_pointer.

> Although this is getting a bit out of this area, imho enter/exit events 
> should be eliminated. There only need to be "move" events, containing 
> the surface they are sent to, the client can detect when the surface 
> changes. There is one hack: if the pointer is moved to another client's 
> surface, the first client gets a move event with a null surface so that 
> does work as an "exit" event, but no extra event type is needed.

So rather than using semantically obvious enter/leave events, you would
rather duplicate the surface designation and event serial in every
motion, button and all other events, causing a more protocol traffic,
and then add hacks to achieve what enter/leave do? I don't think so.
Right now e.g. motion event is the smallest possible: just time and
coordinates.

Note, that wl_pointer.enter is also used in cases where there is no
physical input device action to trigger it. For example, when a window
closes, the pointer can enter the window that was below without any
physical user action. With the current protocol design, motion event is
always from a physical user action, and so we do not need to fake a
timestamp ever. If we had no enter event, motion events would sometimes
have to fake timestamps and perhaps other information. That would be
inconsistent.


Thanks,
pq