[RFC PATCH v2 wayland] protocol: add wl_pointer.axis_source, axis_stop and axis_discrete events

[Peter Hutterer]

The axis_source event determines how an axis event was generated. This enables
clients to judge when to use kinetic scrolling.

The axis_stop event notifies a client about the termination of a scroll
sequence, likewise needed to calculate kinetic scrolling parameters.

The axis_discrete event provides the wheel click count. Previously the axis
value was some hardcoded number (10), with the discrete steps this enables a
client to differ between line-based scrolling on a mouse wheel and smooth
scrolling with a touchpad.

We can't extend the existing wl_pointer.axis events so we introduce a new
concept: latching events. These events (axis_source and axis_discrete)
are prefixed before a wl_pointer.axis or axis_stop event, i.e. the sequence
becomes:

wl_pointer.axis_source
wl_pointer.axis
wl_pointer.axis_source
wl_pointer.axis
wl_pointer.axis_source
wl_pointer.axis
wl_pointer.axis_source
wl_pointer.axis_stop

or:

wl_pointer.axis_source
wl_pointer.axis_discrete
wl_pointer.axis_axis

Clients need to combine the state of all events where needed.
---
Changes to v1:
- introduce axis_stop and axis_discrete as separate events instead of flags
- couple of documentation updates
- wl_seat/keyboard/touch/pointer bumped to version 5

This is for the API review only so far, I don't have the weston patches to
match yet.

 protocol/wayland.xml | 87 +++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 83 insertions(+), 4 deletions(-)

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index c5963e8..29e6f01 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -1337,7 +1337,7 @@
        wl_seat.get_keyboard or wl_seat.get_touch, the returned object is
        always of the same version as the wl_seat.
    -->
-  <interface name="wl_seat" version="4">
+  <interface name="wl_seat" version="5">
     <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
@@ -1411,7 +1411,7 @@
   </interface>
 
   <!-- for the version see the comment in wl_seat -->
-  <interface name="wl_pointer" version="3">
+  <interface name="wl_pointer" version="5">
     <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
@@ -1572,10 +1572,89 @@
       <description summary="release the pointer object"/>
     </request>
 
+    <!-- Version 4 additions: none -->
+
+    <!-- Version 5 additions -->
+
+    <enum name="axis_source">
+      <description summary="axis source types">
+	Describes the axis types of scroll events.
+      </description>
+      <entry name="unknown" value="0"/>
+      <entry name="wheel" value="1"/>
+      <entry name="finger" value="2"/>
+      <entry name="continuous" value="3"/>
+    </enum>
+
+    <event name="axis_source" since="5">
+      <description summary="axis source event">
+        Scroll and other axis source notification.
+
+        This event does not occur on its own. It is sent before a
+        wl_pointer.axis or wl_pointer.axis_stop event and carries the source
+        information for that event. A client is expected to accumulate the
+        data in both events before proceeding.
+
+        The axis and timestamp values are identical to the one in the
+        subsequent wl_pointer.axis or wl_pointer.axis_stop event. For the
+        interpretation of the axis value, see the wl_pointer.axis event
+        documentation.
+
+        The source specifies how this event was generated. If the source is
+        finger, a wl_pointer.axis_stop event will be sent when the user
+        lifts the finger off the device.
+      </description>
+      <arg name="time" type="uint" summary="timestamp with millisecond granularity"/>
+      <arg name="axis" type="uint"/>
+      <arg name="axis_source" type="uint"/>
+    </event>
+
+    <event name="axis_stop" since="5">
+      <description summary="axis stop event">
+        Scroll and other axis stop notification.
+
+        For some wl_pointer.axis_source type, a wl_pointer.axis_stop event
+        is sent to notify a client that the axis sequence has terminated.
+        This enables the client to implement kinetic scrolling.
+        See the wl_pointer.axis_source documentation for information on when
+        this event may be generated.
+
+        Any wl_pointer.axis events after this event should be considered as
+        the start of a new axis motion.
+
+        The axis and timestamp values are to be interpreted identical to the
+        ones in the wl_pointer.axis event.
+      </description>
+      <arg name="time" type="uint" summary="timestamp with millisecond granularity"/>
+      <arg name="axis" type="uint"/>
+    </event>
+
+    <event name="axis_discrete" since="5">
+      <description summary="axis click event">
+        Scroll and other axis discrete step information.
+
+        This event does not occur on its own. It is sent before a
+        wl_pointer.axis event and carries the axis value of the
+        wl_pointer.axis event in discrete steps (e.g. mouse wheel clicks).
+
+        This event is optional, continuous scrolling devices
+        like two-finger scrolling on touchpads do not have discrete
+        steps.
+
+        The axis and timestamp values are to be interpreted identical to the
+        ones in the wl_pointer.axis event.
+
+        The discrete value carries the directional information. e.g. a value
+        of -2 is two steps towards the negative direction of this axis.
+        <arg name="time" type="uint" summary="timestamp with millisecond granularity"/>
+        <arg name="axis" type="uint"/>
+        <arg name="discrete" type="int"/>
+      </description>
+    </event>
   </interface>
 
   <!-- for the version see the comment in wl_seat -->
-  <interface name="wl_keyboard" version="4">
+  <interface name="wl_keyboard" version="5">
     <description summary="keyboard input device">
       The wl_keyboard interface represents one or more keyboards
       associated with a seat.
@@ -1690,7 +1769,7 @@
   </interface>
 
   <!-- for the version see the comment in wl_seat -->
-  <interface name="wl_touch" version="3">
+  <interface name="wl_touch" version="5">
     <description summary="touchscreen input device">
       The wl_touch interface represents a touchscreen
       associated with a seat.
-- 
2.3.3