[PATCH wayland-protocols v2] unstable: Add input-timestamps protocol

[Alexandros Frantzis]

wl_pointer, wl_keyboard and wl_touch events currently use a 32-bit
timestamp with millisecond resolution. In some cases, notably latency
measurements, this resolution is too coarse to be useful.

This protocol provides additional high-resolution timestamps events,
which are emitted before the corresponding input event. Each timestamp
event contains a high-resolution, and ideally higher-accuracy, version
of the 'time' argument of the first subsequent supported input event.

Clients that care about high-resolution timestamps just need to keep
track of the last timestamp event they receive and associate it with the
next supported input event that arrives.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis at collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
Acked-by: Jonas Ådahl <jadahl at gmail.com>
---

Changes in v2:
 - Add '...carrying a timestamp...' to better describe the set of subsequent
   input events in the timestamp event description. 
 - Clarify normalization requirements of tv_sec_hi, tv_sec_lo, tv_nsec
   timestamp representation.

 Makefile.am                                        |   1 +
 unstable/input-timestamps/README                   |   4 +
 .../input-timestamps-unstable-v1.xml               | 145 +++++++++++++++++++++
 3 files changed, 150 insertions(+)
 create mode 100644 unstable/input-timestamps/README
 create mode 100644 unstable/input-timestamps/input-timestamps-unstable-v1.xml

diff --git a/Makefile.am b/Makefile.am
index cabc279..4b9a901 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -16,6 +16,7 @@ unstable_protocols =								\
 	unstable/xwayland-keyboard-grab/xwayland-keyboard-grab-unstable-v1.xml	\
 	unstable/keyboard-shortcuts-inhibit/keyboard-shortcuts-inhibit-unstable-v1.xml \
 	unstable/xdg-output/xdg-output-unstable-v1.xml				\
+	unstable/input-timestamps/input-timestamps-unstable-v1.xml	\
 	$(NULL)
 
 stable_protocols =								\
diff --git a/unstable/input-timestamps/README b/unstable/input-timestamps/README
new file mode 100644
index 0000000..3e82890
--- /dev/null
+++ b/unstable/input-timestamps/README
@@ -0,0 +1,4 @@
+High-resolution timestamps for input events.
+
+Maintainers:
+Alexandros Frantzis <alexandros.frantzis at collabora.com>
diff --git a/unstable/input-timestamps/input-timestamps-unstable-v1.xml b/unstable/input-timestamps/input-timestamps-unstable-v1.xml
new file mode 100644
index 0000000..7c5e082
--- /dev/null
+++ b/unstable/input-timestamps/input-timestamps-unstable-v1.xml
@@ -0,0 +1,145 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="input_timestamps_unstable_v1">
+
+  <copyright>
+    Copyright © 2017 Collabora, Ltd.
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice (including the next
+    paragraph) shall be included in all copies or substantial portions of the
+    Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+  </copyright>
+
+  <description summary="High-resolution timestamps for input events">
+    This protocol specifies a way for a client to request and receive
+    high-resolution timestamps for input events.
+
+    Warning! The protocol described in this file is experimental and
+    backward incompatible changes may be made. Backward compatible changes
+    may be added together with the corresponding interface version bump.
+    Backward incompatible changes are done by bumping the version number in
+    the protocol and interface names and resetting the interface version.
+    Once the protocol is to be declared stable, the 'z' prefix and the
+    version number in the protocol and interface names are removed and the
+    interface version number is reset.
+  </description>
+
+  <interface name="zwp_input_timestamps_manager_v1" version="1">
+    <description summary="context object for high-resolution input timestamps">
+      A global interface used for requesting high-resolution timestamps
+      for input events.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy the input timestamps manager object">
+        Informs the server that the client will no longer be using this
+        protocol object. Existing objects created by this object are not
+        affected.
+      </description>
+    </request>
+
+    <request name="get_keyboard_timestamps">
+      <description summary="subscribe to high-resolution keyboard timestamp events">
+        Creates a new input timestamps object that represents a subscription
+        to high-resolution timestamp events for all wl_keyboard events that
+        carry a timestamp.
+
+        If the associated wl_keyboard object is invalidated, either through
+        client action (e.g. release) or server-side changes, the input
+        timestamps object becomes inert and the client should destroy it
+        by calling zwp_input_timestamps_v1.destroy.
+      </description>
+      <arg name="id" type="new_id" interface="zwp_input_timestamps_v1"/>
+      <arg name="keyboard" type="object" interface="wl_keyboard"
+           summary="the wl_keyboard object for which to get timestamp events"/>
+    </request>
+
+    <request name="get_pointer_timestamps">
+      <description summary="subscribe to high-resolution pointer timestamp events">
+        Creates a new input timestamps object that represents a subscription
+        to high-resolution timestamp events for all wl_pointer events that
+        carry a timestamp.
+
+        If the associated wl_pointer object is invalidated, either through
+        client action (e.g. release) or server-side changes, the input
+        timestamps object becomes inert and the client should destroy it
+        by calling zwp_input_timestamps_v1.destroy.
+      </description>
+      <arg name="id" type="new_id" interface="zwp_input_timestamps_v1"/>
+      <arg name="pointer" type="object" interface="wl_pointer"
+           summary="the wl_pointer object for which to get timestamp events"/>
+    </request>
+
+    <request name="get_touch_timestamps">
+      <description summary="subscribe to high-resolution touch timestamp events">
+        Creates a new input timestamps object that represents a subscription
+        to high-resolution timestamp events for all wl_touch events that
+        carry a timestamp.
+
+        If the associated wl_touch object becomes invalid, either through
+        client action (e.g. release) or server-side changes, the input
+        timestamps object becomes inert and the client should destroy it
+        by calling zwp_input_timestamps_v1.destroy.
+      </description>
+      <arg name="id" type="new_id" interface="zwp_input_timestamps_v1"/>
+      <arg name="touch" type="object" interface="wl_touch"
+           summary="the wl_touch object for which to get timestamp events"/>
+    </request>
+  </interface>
+
+  <interface name="zwp_input_timestamps_v1" version="1">
+    <description summary="context object for input timestamps">
+      Provides high-resolution timestamp events for a set of subscribed input
+      events. The set of subscribed input events is determined by the
+      zwp_input_timestamps_manager_v1 request used to create this object.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy the input timestamps object">
+        Informs the server that the client will no longer be using this
+        protocol object. After the server processes the request, no more
+        timestamp events will be emitted.
+      </description>
+    </request>
+
+    <event name="timestamp">
+      <description summary="high-resolution timestamp event">
+        The timestamp event is associated with the first subsequent input event
+        carrying a timestamp which belongs to the set of input events this
+        object is subscribed to.
+
+        The timestamp provided by this event is a high-resolution version of
+        the timestamp argument of the associated input event. The provided
+        timestamp is in the same clock domain and is at least as accurate as
+        the associated input event timestamp.
+
+        The timestamp is expressed as tv_sec_hi, tv_sec_lo, tv_nsec triples,
+        each component being an unsigned 32-bit value. Whole seconds are in
+        tv_sec which is a 64-bit value combined from tv_sec_hi and tv_sec_lo,
+        and the additional fractional part in tv_nsec as nanoseconds. Hence,
+        for valid timestamps tv_nsec must be in [0, 999999999].
+      </description>
+      <arg name="tv_sec_hi" type="uint"
+           summary="high 32 bits of the seconds part of the timestamp"/>
+      <arg name="tv_sec_lo" type="uint"
+           summary="low 32 bits of the seconds part of the timestamp"/>
+      <arg name="tv_nsec" type="uint"
+           summary="nanoseconds part of the timestamp"/>
+    </event>
+  </interface>
+
+</protocol>
-- 
2.14.1