[PATCH wayland-protocols 1/4] stable: add presentation-time draft

Pekka Paalanen ppaalanen at gmail.com
Mon Feb 22 13:34:40 UTC 2016

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

This XML file has been copied verbatim from Weston 1.10.0 release,
protocol/presentation_timing.xml. The last behavioral change to that
file was in December 2014, so the behaviour is considered stable.

Interfaces still need to be renamed according wayland-protocols policy.
That will be done in a follow-up patch to clearly show the changes.

Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
 stable/presentation-time/README                |   5 +
 stable/presentation-time/presentation-time.xml | 274 +++++++++++++++++++++++++
 2 files changed, 279 insertions(+)
 create mode 100644 stable/presentation-time/README
 create mode 100644 stable/presentation-time/presentation-time.xml

diff --git a/stable/presentation-time/README b/stable/presentation-time/README
new file mode 100644
index 0000000..c7781ea
--- /dev/null
+++ b/stable/presentation-time/README
@@ -0,0 +1,5 @@
+Presentation time protocol
+Pekka Paalanen <pekka.paalanen at collabora.co.uk>
diff --git a/stable/presentation-time/presentation-time.xml b/stable/presentation-time/presentation-time.xml
new file mode 100644
index 0000000..10a5f14
--- /dev/null
+++ b/stable/presentation-time/presentation-time.xml
@@ -0,0 +1,274 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="presentation_timing">
+<!-- wrap:70 -->
+  <copyright>
+    Copyright © 2013-2014 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.
+  </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 identifier 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">
+        These flags provide information about how the presentation of
+        the related content update was done. The intent is to help
+        clients assess the reliability of the feedback and the visual
+        quality with respect to possible tearing and timings. The
+        flags are:
+        VSYNC:
+        The presentation was synchronized to the "vertical retrace" by
+        the display hardware such that tearing does not happen.
+        Relying on user space scheduling is not acceptable for this
+        flag. If presentation is done by a copy to the active
+        frontbuffer, then it must guarantee that tearing cannot
+        happen.
+        HW_CLOCK:
+        The display hardware provided measurements that the hardware
+        driver converted into a presentation timestamp. Sampling a
+        clock in user space is not acceptable for this flag.
+        The display hardware signalled that it started using the new
+        image content. The opposite of this is e.g. a timer being used
+        to guess when the display hardware has switched to the new
+        image content.
+        ZERO_COPY:
+        The presentation of this update was done zero-copy. This means
+        the buffer from the client was given to display hardware as
+        is, without copying it. Compositing with OpenGL counts as
+        copying, even if textured directly from the client buffer.
+        Possible zero-copy cases include direct scanout of a
+        fullscreen surface and a surface on a hardware overlay.
+      </description>
+      <entry name="vsync" value="0x1" summary="presentation was vsync'd"/>
+      <entry name="hw_clock" value="0x2"
+             summary="hardware provided the presentation timestamp"/>
+      <entry name="hw_completion" value="0x4"
+             summary="hardware signalled the start of the presentation"/>
+      <entry name="zero_copy" value="0x8"
+             summary="presentation was done zero-copy"/>
+    </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 preceded 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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