[PATCH v3] protocol: Extend wl_touch with touchpoint shape event

[Yong Bakos]

On Apr 14, 2016, at 3:23 PM, Dennis Kempin <denniskempin at google.com> 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>

Hi Dennis,
I've noted some concerns inline below. I'm a bit inexperienced here, so
please do correct/educate me where I'm wrong.


> ---
> protocol/wayland.xml | 75 ++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 64 insertions(+), 11 deletions(-)
> 
> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> index 12a6efd..d19d898 100644
> --- a/protocol/wayland.xml
> +++ b/protocol/wayland.xml
> @@ -910,11 +910,6 @@
>       copy-and-paste and drag-and-drop.  These mechanisms are tied to
>       a wl_seat and this interface lets a client get a wl_data_device
>       corresponding to a wl_seat.
> -
> -      Depending on the version bound, the objects created from the bound
> -      wl_data_device_manager object will have different requirements for
> -      functioning properly. See wl_data_source.set_actions,
> -      wl_data_offer.accept and wl_data_offer.finish for details.

What does the deletion of this paragraph have to do with adding the
two new touchpoint shape events?


>     </description>
> 
>     <request name="create_data_source">
> @@ -1656,7 +1651,7 @@
>     </request>
>    </interface>
> 
> -  <interface name="wl_seat" version="5">
> +  <interface name="wl_seat" version="6">

Why are you bumping this instead of just bumping the version of the 
wl_touch interface?


>     <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 +1760,7 @@
> 
>   </interface>
> 
> -  <interface name="wl_pointer" version="5">
> +  <interface name="wl_pointer" version="6">

Why are you bumping this instead of just bumping the version of the 
wl_touch interface?


>     <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
> @@ -2038,7 +2033,7 @@
> 
>  The timestamp is to be interpreted identical to the timestamp in the
>  wl_pointer.axis event. The timestamp value may be the same as a
> - preceding wl_pointer.axis event.
> + preceeding wl_pointer.axis event.

Why are you introducing a misspelling?


>       </description>
>       <arg name="time" type="uint" summary="timestamp with
> millisecond granularity"/>
>       <arg name="axis" type="uint" enum="axis" summary="the axis
> stopped with this event"/>
> @@ -2078,7 +2073,7 @@
>     </event>
>   </interface>
> 
> -  <interface name="wl_keyboard" version="5">
> +  <interface name="wl_keyboard" version="6">

Why are you bumping this instead of just bumping the version of the 
wl_touch interface?


>     <description summary="keyboard input device">
>       The wl_keyboard interface represents one or more keyboards
>       associated with a seat.
> @@ -2192,7 +2187,7 @@
>     </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 +2237,12 @@
> 
>     <event name="frame">
>       <description summary="end of touch frame event">
> - Indicates the end of a contact point list.
> +  Indicates the end of a contract point list. The wayland protocol requires

contact point list.


> +  touch point updates to be sent sequentially, however all events within a
> +  frame should be considered one hardware event. A wl_touch.frames terminates

wl_touch.frame


> +  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.

Am I misreading this or has indentation been obliterated?


>       </description>
>     </event>
> 
> @@ -2262,6 +2262,59 @@
>     <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.

Same paragraph? And indentation?


> +  The protocol does not guarantee specific ordering of wl_touch.orientation,
> +  wl_touch.shape and wl_touch.motion events.
> +
> +  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.
> +  Both are specified in surface coordinates.
> +  The center of the ellipse is always at the touchpoint location as reported

Same paragraph? And indentation?


> +  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.

This last sentence seems unnecessary.


> +      </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 coordinates"/>
> +      <arg name="minor" type="fixed" summary="length of the minor
> axis in surface coordinates"/>

I politely encourage "surface local coordinates."
https://lists.freedesktop.org/archives/wayland-devel/2016-April/027804.html


> +    </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.
> +
> +  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.
> +  The client has to make reasonable assumptions about the orientation if
> +  it did not receive this event.

As mentioned in the shape event, I feel this last sentence is unnecessary.
And, am I misreading or is the indentation missing?

> +      </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"/>
> +    </event>
> +

Omitting this line break would match the current convention.

>   </interface>
> 
>   <interface name="wl_output" version="2">
> --
> 2.8.0.rc3.226.g39d4020
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