[PATCH weston v2 1/5] protocol: Add _wl_pointer_gestures (swipe/pinch) protocol

[Jonas Ådahl]

On Thu, Feb 18, 2016 at 10:03:36AM +0000, Daniel Stone wrote:
> Hi,
> 
> On 31 July 2015 at 14:53, Carlos Garnacho <carlosg at gnome.org> wrote:
> > On Wed, Jul 29, 2015 at 4:52 AM, Jonas Ådahl <jadahl at gmail.com> wrote:
> >> On Thu, Jul 23, 2015 at 07:00:27PM +0200, Carlos Garnacho wrote:
> >>> +<protocol name="pointer_gestures">
> >>> +  <interface name="_wl_pointer_gestures" version="1">
> >>> +    <description summary="touchpad gestures">
> >>> +      A global interface to provide semantic touchpad gestures for a given
> >>> +      pointer.
> >>> +
> >>> +      Two gestures are currently supported: swipe and zoom/rotate.
> >>> +      All gestures follow a three-stage cycle: begin, update, end and
> >>> +      are identified by a unique id.
> >>> +
> >>> +      Warning! The protocol described in this file is experimental. Each
> >>> +      version of this protocol should be considered incompatible with any
> >>> +      other version, and a client binding to a version different to the one
> >>> +      advertised will be terminated. Once the protocol is declared stable,
> >>> +      compatibility is guaranteed, the '_' prefix will be removed from the
> >>> +      name and the version will be reset to 1.
> >>> +    </description>
> >>> +
> >>> +    <request name="get_swipe_gesture">
> >>> +      <description summary="get swipe gesture">
> >>> +     Create a swipe gesture object. See the
> >>> +     wl_pointer_gesture_swipe interface for details.
> >>> +      </description>
> >>> +      <arg name="id" type="new_id" interface="_wl_pointer_gesture_swipe"/>
> >>> +      <arg name="pointer" type="object" interface="wl_pointer"/>
> >>> +    </request>
> >>> +
> >>> +    <request name="get_pinch_gesture">
> >>> +      <description summary="get pinch gesture">
> >>> +     Create a pinch gesture object. See the
> >>> +     wl_pointer_gesture_pinch interface for details.
> >>> +      </description>
> >>> +      <arg name="id" type="new_id" interface="_wl_pointer_gesture_pinch"/>
> >>> +      <arg name="pointer" type="object" interface="wl_pointer"/>
> >>> +    </request>
> >>> +  </interface>
> 
> One suggestion I'd have is to register surfaces explicitly, i.e.:
> <request name="add_surface">
>   <description summary="register interest for gestures on a particular surface">
>     Adds the surface to the list of surfaces which will receive
> gesture events. Each surface may only be registered on one
> wl_gesture_manager object.
>   </description>
>   <arg name="surface" type="object" interface="wl_surface"/>
>   <enum name="gestures" description="gestures the client is interested in"/>
> </request>

Doesn't feel right and I don't really see the point. I interpret this
extension as an adde feature to *pointer* devices, and it should follow
pointer focus and not diverge too much from how a pointer works / emits
events.

> 
> >>> +  <interface name="_wl_pointer_gesture_swipe" version="1">
> >>> +    <description summary="a swipe gesture object">
> >>> +      A swipe gesture object notifies a client about a multi-finger swipe
> >>> +      gesture detected on an indirect input device such as a touchpad.
> >>> +      The gesture is usually initiated by multiple fingers moving in the
> >>> +      same direction but once initiated the direction may change.
> >>> +      The precise conditions of when such a gesture is detected are
> >>> +      implementation-dependent.
> >>> +
> >>> +      A gesture consists of three stages: begin, update (optional) and end.
> >>> +      There cannot be multiple simultaneous pinch or swipe gestures, how
> >>> +      compositors prevent these situations is implementation-dependent.
> >>
> >> There cannot be multiple simultaneous gestures one one seat. There can
> >> be multiple gestures but that means they are on different seats.
> >
> > Right, that's the idea. On multi-seat, there would be several
> > wl_pointers, and each could be able to perform gestures individually.
> > I reworded the docs blurb to be more specific there.
> 
> That works for touchpads (what I assume this was designed against),
> but breaks for multitouch touchscreens: there you could be
> pinching/zooming/scrolling/etc in multiple areas at the same time. I'd
> prefer to see the individual gestures (swipe/etc) come in as new_id
> events, which would allow multiple simultaneous gestures.

Gestures for touch screens etc I would assume would be done client side,
i.e. they wouldn't use this protocol at all.

Now, one could have multiple touchpads and gesture on more than one
which I assume would be broken now, but not sure that's a reasonable
enough use case.


Jonas

> 
> >>> +      A gesture may be cancelled by the compositor or the hardware.
> >>> +      Destructive actions should not be considered until the end of a
> >>> +      gesture has been received.
> >>
> >> Does this mean that a client may not destroy a gesture object after a
> >> "begin" before an "end"? Why should that not be allowed?
> >
> > As Peter said, that's rather a remark for clients, changed the wording
> > ("permanent or irreversible" instead of "destructive"), and made it
> > clear it's specific to clients.
> 
> What does 'clients not should consider a destructive action ...' mean?
> Does it mean that you aren't allowed to close a client until a gesture
> has ended?
> 
> Cheers,
> Daniel