| <?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> |
