[PATCH] Add touch events to protocol.

[Kristian Høgsberg]

On Tue, Jul 5, 2011 at 1:08 PM, Chase Douglas
<chase.douglas at canonical.com> wrote:
> Hi Laszlo,
>
> On 06/29/2011 07:54 AM, Laszlo Agocs wrote:
>>
>>  From f656362511e2622e3cde6062e156b59a83b50e03 Mon Sep 17 00:00:00 2001
>> From: Laszlo Agocs <laszlo.p.agocs at nokia.com>
>> Date: Wed, 29 Jun 2011 17:51:29 +0300
>> Subject: [PATCH] Add touch events to protocol.
>>
>> ---
>>   protocol/wayland.xml |   39 +++++++++++++++++++++++++++++++++++++++
>>   1 files changed, 39 insertions(+), 0 deletions(-)
>>
>> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
>> index fd54245..874fd5f 100644
>> --- a/protocol/wayland.xml
>> +++ b/protocol/wayland.xml
>> @@ -461,6 +461,45 @@
>>         <arg name="surface" type="object" interface="wl_surface"/>
>>         <arg name="keys" type="array"/>
>>       </event>
>> +
>> +    <!-- A notification that is to be sent at least once to each
>> +         client, defining the range of coordinates used by the touch
>> +         device. -->
>> +    <event name="touch_configure">
>> +      <arg name="min_x" type="int" />
>> +      <arg name="max_x" type="int" />
>> +      <arg name="min_y" type="int" />
>> +      <arg name="max_y" type="int" />
>> +    </event>
>> +
>> +    <event name="touch_down">
>> +      <arg name="time" type="uint"/>
>> +      <arg name="id" type="int" />
>> +      <arg name="x" type="int" />
>> +      <arg name="y" type="int" />
>> +    </event>
>> +
>> +    <event name="touch_up">
>> +      <arg name="time" type="uint"/>
>> +      <arg name="id" type="int" />
>> +    </event>
>> +
>> +    <event name="touch_motion">
>> +      <arg name="time" type="uint"/>
>> +      <arg name="id" type="int" />
>> +      <arg name="x" type="int" />
>> +      <arg name="y" type="int" />
>> +    </event>
>
> What about pressure or shape? I don't know the wayland protocol yet, but
> is it possible to send a map of properties and values sort of like
> valuators?
>
>> +
>> +    <!-- Indicates the end of a contact point list. -->
>> +    <event name="touch_frame">
>> +    </event>
>> +
>> +    <!-- Sent if the compositor decides the touch stream is a global
>> +         gesture. No further events are sent to the clients from that
>> +         particular gesture. -->
>> +    <event name="touch_cancel">
>> +    </event>
>>     </interface>
>
> I never understood the concept behind "touch cancel". If I'm a client,
> I'm supposed to sit around waiting for a touch cancel event at any
> point? Is it bounded in time, or could I get a touch cancel event 20
> seconds into a stream of motion events? I don't see a way to get around
> explicitly conferring whether a touch  is "accepted" or "rejected"
> (implicitly or explicitly) at some point, which is what XInput 2.1 is
> aiming to do. However, the exact mechanisms may be different in Wayland
> since we don't have the old X cruft to deal with.

Yes, any stream of touch event, no matter how long, can be cancelled
by the compositor at any time.  The use cases are when the compositor
recognizes a global gesture (three finger pinch to go to home screen
or so) or if an important system event happens (incoming phone call or
such).

Whether and how to undo the effects of the touch events up until the
cancel is an application policy decision.  If you're just scrolling a
browser window, it probably doesn't make sense to undo the scrolling.
Even if you're, say, painting in a paint app, it probably makes sense
to just treat cancel as end and commit the paint action, provided the
user can just undo that if necessary.

In general, undoing the touch stream is similar to undo, which most
apps are already handling.  From an application point of view, if you
have to handle unowned events (that's the XI 2.1 term, right?) for a
small initial window (100ms, 3s or a week), you end up with the same
application side complexity, and I don't see what it is apps can do
differently once they know that the remaining event stream belongs to
them.

Kristian