[PATCH 1/8] protocol: add presentation extension v5

Louis-Francis Ratté-Boulianne lfrb at collabora.com
Tue Sep 23 19:08:42 PDT 2014

From: Pekka Paalanen <pekka.paalanen at collabora.co.uk>

Add accurate presentation timing features to Wayland: queueing and

This specification is based on the draft written by Frederic Plourde
<frederic.plourde at collabora.co.uk> and redesigned by Pekka Paalanen.

The RFC v2 version is from

Changes in v3:

* associate presentation time to current surface contents

This implements the suggestion from

which prevents surface content from jumping backwards in time if a
client retroactively queues an update with a target time in the past.

* use 64-bit tv_sec in presentation

The time_t type used in struct timespec could be almost anything. POSIX
probably defines it to be an integer, but not the size. Apparently it is
usually 'long', which makes it 64-bit on x86_64.

To be able to fully represent timespec values returned by clock_gettime,
change the protocol to use 64 bits for the tv_sec part.

* define an error for invalid tv_nsec

This allow us to rely on the normalized timestamp form.

* define some interactions with sub-surfaces

Sub-surface cached state updates (synchronized mode) are designed
especially for resizing. As queued updates are not meant to produce any
resizing-like effects, they also do not trigger any sub-surface

* add sub-headings as xml comments

* queued update cannot map

Because before mapping, the surface has no main output assigned. An
immediate commit is needed anyway, to be able to set all the surface
state, which a queued update cannot touch.

* frame callbacks are not queued

It is not known when queueing frame callbacks would be useful.

Changes in v4:

* remove mentions of the queuing feature

The specification has been split and the queuing feature will be added
back in another version of the extension.

* add flags argument to 'presented' event

Describe the nature of how the update was presented to screen and the
characteristics of the feedback information. No flags have been
defined for now.

* add a protocol error code for invalid flags

Changes in v5:

* remove the destroy method for the feedback object

The protocol object should instead be automatically destroyed after
a 'presented' or 'discarded' event has been triggered.

* some grammatical corrections to the specification

[Louis-Francis Ratté-Boulianne: split the spec in two parts]

Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
Signed-off-by: Louis-Francis Ratté-Boulianne <lfrb at collabora.com>
Reviewed-by: Mario Kleiner <mario.kleiner.de at gmail.com>
 Makefile.am                      |   5 +
 protocol/presentation_timing.xml | 238 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 243 insertions(+)
 create mode 100644 protocol/presentation_timing.xml

diff --git a/Makefile.am b/Makefile.am
index b2d6893..b1dcc21 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -78,6 +78,8 @@ nodist_weston_SOURCES =					\
 	protocol/input-method-server-protocol.h		\
 	protocol/workspaces-protocol.c			\
 	protocol/workspaces-server-protocol.h		\
+	protocol/presentation_timing-protocol.c		\
+	protocol/presentation_timing-server-protocol.h	\
 	protocol/scaler-protocol.c			\
@@ -445,6 +447,8 @@ nodist_libtoytoolkit_la_SOURCES =			\
 	protocol/scaler-client-protocol.h		\
 	protocol/workspaces-protocol.c			\
 	protocol/workspaces-client-protocol.h		\
+	protocol/presentation_timing-protocol.c		\
+	protocol/presentation_timing-client-protocol.h	\
 	protocol/xdg-shell-protocol.c			\
@@ -987,6 +991,7 @@ EXTRA_DIST +=					\
 	protocol/wayland-test.xml		\
 	protocol/xdg-shell.xml			\
 	protocol/fullscreen-shell.xml		\
+	protocol/presentation_timing.xml	\
 man_MANS = weston.1 weston.ini.5
diff --git a/protocol/presentation_timing.xml b/protocol/presentation_timing.xml
new file mode 100644
index 0000000..9158434
--- /dev/null
+++ b/protocol/presentation_timing.xml
@@ -0,0 +1,238 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="presentation_timing">
+<!-- wrap:70 -->
+  <copyright>
+    Copyright © 2013-2014 Collabora, Ltd.
+    Permission to use, copy, modify, distribute, and sell this
+    software and its documentation for any purpose is hereby granted
+    without fee, provided that the above copyright notice appear in
+    all copies and that both that copyright notice and this permission
+    notice appear in supporting documentation, and that the name of
+    the copyright holders not be used in advertising or publicity
+    pertaining to distribution of the software without specific,
+    written prior permission.  The copyright holders make no
+    representations about the suitability of this software for any
+    purpose.  It is provided "as is" without express or implied
+    warranty.
+  </copyright>
+  <interface name="presentation" version="1">
+    <description summary="timed presentation related wl_surface requests">
+<!-- Introduction -->
+      The main feature of this interface is accurate presentation
+      timing feedback to ensure smooth video playback while maintaining
+      audio/video synchronization. Some features use the concept of a
+      presentation clock, which is defined in presentation.clock_id
+      event.
+      Request 'feedback' can be regarded as an additional wl_surface
+      method. It is part of the double-buffered surface state update
+      mechanism, where other requests first set up the state and then
+      wl_surface.commit atomically applies the state into use. In
+      other words, wl_surface.commit submits a content update.
+<!-- Completing presentation -->
+      When the final realized presentation time is available, e.g.
+      after a framebuffer flip completes, the requested
+      presentation_feedback.presented events are sent. The final
+      presentation time can differ from the compositor's predicted
+      display update time and the update's target time, especially
+      when the compositor misses its target vertical blanking period.
+    </description>
+    <enum name="error">
+      <description summary="fatal presentation errors">
+        These fatal protocol errors may be emitted in response to
+        illegal presentation requests.
+      </description>
+      <entry name="invalid_timestamp" value="0"
+             summary="invalid value in tv_nsec"/>
+      <entry name="invalid_flag" value="1"
+             summary="invalid flag"/>
+    </enum>
+    <request name="destroy" type="destructor">
+      <description summary="unbind from the presentation interface">
+        Informs the server that the client will not be using this
+        protocol object anymore. This does not affect any existing
+        objects created by this interface.
+      </description>
+    </request>
+    <request name="feedback">
+      <description summary="request presentation feedback information">
+        Request presentation feedback for the current content submission
+        on the given surface. This creates a new presentation_feedback
+        object, which will deliver the feedback information once. If
+        multiple presentation_feedback objects are created for the same
+        submission, they will all deliver the same information.
+        For details on what information is returned, see
+        presentation_feedback interface.
+      </description>
+      <arg name="surface" type="object" interface="wl_surface"
+           summary="target surface"/>
+      <arg name="callback" type="new_id" interface="presentation_feedback"
+           summary="new feedback object"/>
+    </request>
+    <event name="clock_id">
+      <description summary="clock ID for timestamps">
+        This event tells the client in which clock domain the
+        compositor interprets the timestamps used by the presentation
+        extension. This clock is called the presentation clock.
+        The compositor sends this event when the client binds to the
+        presentation interface. The presentation clock does not change
+        during the lifetime of the client connection.
+        The clock identifier is platform dependent. Clients must be
+        able to query the current clock value directly, not by asking
+        the compositor.
+        On Linux/glibc, the identifer value is one of the clockid_t
+        values accepted by clock_gettime(). clock_gettime() is defined
+        by POSIX.1-2001.
+        Compositors should prefer a clock which does not jump and is
+        not slewed e.g. by NTP. The absolute value of the clock is
+        irrelevant. Precision of one millisecond or better is
+        recommended.
+        Timestamps in this clock domain are 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].
+        Note that clock_id applies only to the presentation clock,
+        and implies nothing about e.g. the timestamps used in the
+        Wayland core protocol input events.
+      </description>
+      <arg name="clk_id" type="uint" summary="platform clock identifier"/>
+    </event>
+  </interface>
+  <interface name="presentation_feedback" version="1">
+    <description summary="presentation time feedback event">
+      A presentation_feedback object returns an indication that a
+      wl_surface content update has become visible to the user.
+      One object corresponds to one content update submission
+      (wl_surface.commit). There are two possible outcomes: the
+      content update is presented to the user, and a presentation
+      timestamp delivered; or, the user did not see the content
+      update because it was superseded or its surface destroyed,
+      and the content update is discarded.
+      Once a presentation_feedback object has delivered an 'presented'
+      or 'discarded' event it is automatically destroyed.
+    </description>
+    <event name="sync_output">
+      <description summary="presentation synchronized to this output">
+        As presentation can be synchronized to only one output at a
+        time, this event tells which output it was. This event is only
+        sent prior to the presented event.
+        As clients may bind to the same global wl_output multiple
+        times, this event is sent for each bound instance that matches
+        the synchronized output. If a client has not bound to the
+        right wl_output global at all, this event is not sent.
+      </description>
+      <arg name="output" type="object" interface="wl_output"
+           summary="presentation output"/>
+    </event>
+    <enum name="kind">
+      <description summary="bitmask of flags in presented event">
+      </description>
+      <entry name="none" value="0"/>
+    </enum>
+    <event name="presented">
+      <description summary="the content update was displayed">
+        The associated content update was displayed to the user at the
+        indicated time (tv_sec_hi/lo, tv_nsec). For the interpretation of
+        the timestamp, see presentation.clock_id event.
+        The timestamp corresponds to the time when the content update
+        turned into light the first time on the surface's main output.
+        Compositors may approximate this from the framebuffer flip
+        completion events from the system, and the latency of the
+        physical display path if known.
+        This event is preceeded by all related sync_output events
+        telling which output's refresh cycle the feedback corresponds
+        to, i.e. the main output for the surface. Compositors are
+        recommended to choose the output containing the largest part
+        of the wl_surface, or keeping the output they previously
+        chose. Having a stable presentation output association helps
+        clients predict future output refreshes (vblank).
+        Argument 'refresh' gives the compositor's prediction of how
+        many nanoseconds after tv_sec, tv_nsec the very next output
+        refresh may occur. This is to further aid clients in
+        predicting future refreshes, i.e., estimating the timestamps
+        targeting the next few vblanks. If such prediction cannot
+        usefully be done, the argument is zero.
+        The 64-bit value combined from seq_hi and seq_lo is the value
+        of the output's vertical retrace counter when the content
+        update was first scanned out to the display. This value must
+        be compatible with the definition of MSC in
+        GLX_OML_sync_control specification. Note, that if the display
+        path has a non-zero latency, the time instant specified by
+        this counter may differ from the timestamp's.
+        If the output does not have a constant refresh rate, explicit
+        video mode switches excluded, then the refresh argument must
+        be zero.
+        If the output does not have a concept of vertical retrace or a
+        refresh cycle, or the output device is self-refreshing without
+        a way to query the refresh count, then the arguments seq_hi
+        and seq_lo must be zero.
+      </description>
+      <arg name="tv_sec_hi" type="uint"
+           summary="high 32 bits of the seconds part of the presentation timestamp"/>
+      <arg name="tv_sec_lo" type="uint"
+           summary="low 32 bits of the seconds part of the presentation timestamp"/>
+      <arg name="tv_nsec" type="uint"
+           summary="nanoseconds part of the presentation timestamp"/>
+      <arg name="refresh" type="uint" summary="nanoseconds till next refresh"/>
+      <arg name="seq_hi" type="uint"
+           summary="high 32 bits of refresh counter"/>
+      <arg name="seq_lo" type="uint"
+           summary="low 32 bits of refresh counter"/>
+      <arg name="flags" type="uint" summary="combination of 'kind' values"/>
+    </event>
+    <event name="discarded">
+      <description summary="the content update was not displayed">
+        The content update was never displayed to the user.
+      </description>
+    </event>
+  </interface>

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