[PATCH v3] protocol: Extend wl_touch with touchpoint shape and orientation

Tue Apr 19 04:49:50 UTC 2016

On Mon, Apr 18, 2016 at 12:36:39PM +0800, Jonas Ådahl wrote:
> On Fri, Apr 15, 2016 at 08:01:35AM -0700, Dennis Kempin wrote:
> > This CL updates the wl_touch interface with a shape and
> > orientation event.
> > The shape/orientation of a touch point is not relevant for most UI
> > applications, but allows a better experience in some cases
> > such as drawing apps.
> > 
> > The events are used by the compositor to inform the client
> > about changes in the shape and orientation of a touchpoint, which is
> > approximated by an ellipse and it's angle to the y-axis.
> > 
> > The event is optional and only sent when compositor and the
> > touch device support this type of information. The client is
> > responsible for making a reasonable assumption about the
> > touch shape if no shape is reported.
> > 
> > Signed-off-by: Dennis Kempin <denniskempin at google.com>
> > ---
> >  protocol/wayland.xml | 64 ++++++++++++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 59 insertions(+), 5 deletions(-)
> > 
> > diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> > index 12a6efd..b8a9835 100644
> > --- a/protocol/wayland.xml
> > +++ b/protocol/wayland.xml
> > @@ -1656,7 +1656,7 @@
> >      </request>
> >     </interface>
> > 
> > -  <interface name="wl_seat" version="5">
> > +  <interface name="wl_seat" version="6">
> >      <description summary="group of input devices">
> >        A seat is a group of keyboards, pointer and touch devices. This
> >        object is published as a global during start up, or when such a
> > @@ -1765,7 +1765,7 @@
> > 
> >    </interface>
> > 
> > -  <interface name="wl_pointer" version="5">
> > +  <interface name="wl_pointer" version="6">
> >      <description summary="pointer input device">
> >        The wl_pointer interface represents one or more input devices,
> >        such as mice, which control the pointer location and pointer_focus
> > @@ -2078,7 +2078,7 @@
> >      </event>
> >    </interface>
> > 
> > -  <interface name="wl_keyboard" version="5">
> > +  <interface name="wl_keyboard" version="6">
> >      <description summary="keyboard input device">
> >        The wl_keyboard interface represents one or more keyboards
> >        associated with a seat.
> > @@ -2192,7 +2192,7 @@
> >      </event>
> >    </interface>
> > 
> > -  <interface name="wl_touch" version="5">
> > +  <interface name="wl_touch" version="6">
> >      <description summary="touchscreen input device">
> >        The wl_touch interface represents a touchscreen
> >        associated with a seat.
> > @@ -2242,7 +2242,12 @@
> > 
> >      <event name="frame">
> >        <description summary="end of touch frame event">
> > - Indicates the end of a contact point list.
> > + Indicates the end of a contact point list. The wayland protocol requires
> > + touch point updates to be sent sequentially, however all events within a
> > + frame should be considered one hardware event. A wl_touch.frame terminates
> > + at least one event but otherwise no guarantee is provided about the set of
> > + events within a frame. A client must assume that any state not updated in a
> > + frame is unchanged from the previously known state.
> 
> Seems to be some formatting error. This paragraph should be indented
> with one tab, not one space. Same with the description in "shape" and
> "orientation".
> 
> I think this part should be a separate patch. Also no need to point out
> that this is the wayland protocol. I'd also suggest avoiding stating
> that they are considered one hardware event. It'd probably be better to
> follow what wl_pointer says here and say that they "logically belong
> together". Check out wl_pointer.frame for some inspiration.

ftr, that's is the wording we used in the tablet protocol for the frame
events:
        Marks the end of a series of axis and/or button updates from the
        tablet. The wayland protocol requires axis updates to be sent
        sequentially, however all events within a frame should be considered
        one hardware event.
but I agree that the wl_pointer.frame wording is better here.

> >        </description>
> >      </event>
> > 
> > @@ -2262,6 +2267,55 @@
> >      <request name="release" type="destructor" since="3">
> >        <description summary="release the touch object"/>
> >      </request>
> > +
> > +    <!-- Version 6 additions -->
> > +
> > +    <event name="shape" since="6">
> > +      <description summary="update shape of touch point">
> > + Sent when a touchpoint has changed its shape. If the touch position
> > + or orientation changed at the same time, the wl_touch.motion,
> > + wl_touch.orientation and wl_touch.shape are sent within the same
> > + wl_touch.frame. Otherwise, only a wl_touch.shape is sent within this
> > + wl_touch.frame. The protocol does not guarantee specific ordering of
> > + wl_touch.orientation, wl_touch.shape and wl_touch.motion events.
> 
> I'd suggest changing this paragraph to be more clear that the
> non-guarantees of what may be sent together, while avoiding the wording
> "at the same time". Something like
> 
> 	Sent when a touchpoint has changed its shape.
> 
> 	This event event does not occur on its own. It is sent before a
> 	wl_touch.frame event, and carries the new shape information for
> 	the specific touch points for that frame.

I don't think you need the ',' here

> 	
> 	This event may be sent alone or together with other events
> 	describing the touch point, such as wl_touch.motion and
> 	wl_touch.orientation. The order of wl_touch.shape,
> 	wl_touch.orientation and wl_touch.motion is not guaranteed.

"alone" and "together" aren't perfectly defined either, how about:
    Other events describing the touch point such as wl_touch.motion or
    wl_touch.orientation may be sent within the same wl_touch.frame. A
    client should treat these events as a single logical touch point update.
    The order of ...

> 
> > +
> > + A touchpoint shape is approximated by an ellipse through the major and minor
> > + axis length. The major axis length describes the longest diameter of the
> > + ellipse, while the minor axis length describes the shortest diameter.

longest->longer, shortest->shorter and add "Major and minor are orthogonal"

> > + Both are specified in surface coordinates. The center of the ellipse is
> > + always at the touchpoint location as reported by wl_touch.down or
> > + wl_touch.move.
> > +
> > + This event is only sent by the compositor if the touch device supports shape
> > + reports. The client has to make reasonable assumptions about the shape if
> > + it did not receive this event.
> > +      </description>
> > +      <arg name="id" type="int" summary="the unique ID of this touch point"/>
> > +      <arg name="major" type="fixed" summary="length of the major
> > axis in surface local coordinates"/>
> > +      <arg name="minor" type="fixed" summary="length of the minor
> > axis in surface local coordinates"/>

don't you need a dash here: surface-local? or is that american vs british
english?

> > +    </event>
> > +
> > +    <event name="orientation" since="6">
> > +      <description summary="update orientation of touch point">
> > + Sent when a touchpoint has changed its orientation. If the touch position
> > + or shape changed at the same time, the wl_touch.motion, wl_touch.orientation
> > + and wl_touch.shape are sent within the same wl_touch.frame.
> > + Otherwise, only a wl_touch.orientation is sent within this wl_touch.frame.
> > + The protocol does not guarantee specific ordering of wl_touch.orientation,
> > + wl_touch.shape and wl_touch.motion events.
> 
> Same suggested rewording as for the "shape" event.
> 
> 
> Jonas
> 
> > +
> > + The orientation describes the clockwise angle of touchpoints major axis to
> > + the surface y-axis and is normalized to the -180 to +180 degrees range.
> > + The granuality of orientation depends on the touch device, some devices only
> > + support binary rotation values between 0 and 90 degrees.
> > +
> > + This event is only sent by the compositor if the touch device supports
> > + orientation reports.
> > +      </description>
> > +      <arg name="id" type="int" summary="the unique ID of this touch point"/>
> > +      <arg name="orientation" type="fixed" summary="angle between
> > major axis and surface y-axis in degrees"/>

you need to specify the direction of the y axis too, because the angle could
be cw or ccw and could be off the negative or positive y axis.

this is all just making sure we are precise enough, the actual protocol
looks good, thanks.

Cheers,
  Peter

> > +    </event>
> > +
> >    </interface>
> > 
> >    <interface name="wl_output" version="2">