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<?xml version="1.0" encoding="UTF-8"?>
<protocol name="presentation_time">
<!-- 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.
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>
<interface name="wp_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 the
presentation.clock_id event.
A content update for a wl_surface is submitted by a
wl_surface.commit request. Request 'feedback' associates with
the wl_surface.commit and provides feedback on the content
update, particularly the final realized presentation time.
<!-- 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 no longer be using
this protocol object. Existing objects created by this object
are not affected.
</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 the
presentation_feedback interface.
</description>
<arg name="surface" type="object" interface="wl_surface"
summary="target surface"/>
<arg name="callback" type="new_id" interface="wp_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. 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.
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.
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. Clients must be able to query the current clock
value directly, not by asking the compositor.
</description>
<arg name="clk_id" type="uint" summary="platform clock identifier"/>
</event>
</interface>
<interface name="wp_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 a '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.
HW_COMPLETION:
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).
The 'refresh' argument 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.
If the output does not have a constant refresh rate, explicit
video mode switches excluded, then the refresh argument must
be 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 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>
</protocol>