third_party/mutter/wayland_protocols/fifo-v1.xml

<?xml version="1.0" encoding="UTF-8"?>
<protocol name="fifo_v1">
  <copyright>
    Copyright © 2023 Valve Corporation

    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,
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    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice (including the next
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    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_fifo_manager_v1" version="1">
    <description summary="protocol for fifo constraints">
      When a Wayland compositor considers applying a content update,
      it must ensure all the update's readiness constraints (fences, etc)
      are met.

      This protocol provides a way to use the completion of a display refresh
      cycle as an additional readiness constraint.

      Warning! The protocol described in this file is currently in the testing
      phase. Backward compatible changes may be added together with the
      corresponding interface version bump. Backward incompatible changes can
      only be done by creating a new major version of the extension.
    </description>

    <enum name="error">
      <description summary="fatal presentation error">
        These fatal protocol errors may be emitted in response to
        illegal requests.
      </description>
      <entry name="already_exists" value="0"
             summary="fifo manager already exists for surface"/>
    </enum>

    <request name="destroy" type="destructor">
      <description summary="unbind from the manager 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="get_fifo">
      <description summary="request fifo interface for surface">
        Establish a fifo object for a surface that may be used to add
        display refresh constraints to content updates.

        Only one such object may exist for a surface and attempting
        to create more than one will result in an already_exists
        protocol error. If a surface is acted on by multiple software
        components, general best practice is that only the component
        performing wl_surface.attach operations should use this protocol.
      </description>
      <arg name="id" type="new_id" interface="wp_fifo_v1"/>
      <arg name="surface" type="object" interface="wl_surface"/>
    </request>
  </interface>

  <interface name="wp_fifo_v1" version="1">
    <description summary="fifo interface">
      A fifo object for a surface that may be used to add
      display refresh constraints to content updates.
    </description>

    <enum name="error">
      <description summary="fatal error">
        These fatal protocol errors may be emitted in response to
        illegal requests.
      </description>
      <entry name="surface_destroyed" value="0"
             summary="the associated surface no longer exists"/>
    </enum>

    <request name="set_barrier">
      <description summary="sets the start point for a fifo constraint">
        When the content update containing the "set_barrier" is applied,
        it sets a "fifo_barrier" condition on the surface associated with
        the fifo object. The condition is cleared immediately after the
        following latching deadline for non-tearing presentation.

        The compositor may clear the condition early if it must do so to
        ensure client forward progress assumptions.

        To wait for this condition to clear, use the "wait_barrier" request.

        "set_barrier" is double-buffered state, see wl_surface.commit.

        Requesting set_barrier after the fifo object's surface is
        destroyed will generate a "surface_destroyed" error.
      </description>
    </request>

    <request name="wait_barrier">
      <description summary="adds a fifo constraint to a content update">
        Indicate that this content update is not ready while a
        "fifo_barrier" condition is present on the surface.

        This means that when the content update containing "set_barrier"
        was made active at a latching deadline, it will be active for
        at least one refresh cycle. A content update which is allowed to
        tear might become active after a latching deadline if no content
        update became active at the deadline.

        The constraint must be ignored if the surface is a subsurface in
        synchronized mode. If the surface is not being updated by the
        compositor (off-screen, occluded) the compositor may ignore the
        constraint. Clients must use an additional mechanism such as
        frame callbacks or timestamps to ensure throttling occurs under
        all conditions.

        "wait_barrier" is double-buffered state, see wl_surface.commit.

        Requesting "wait_barrier" after the fifo object's surface is
        destroyed will generate a "surface_destroyed" error.
      </description>
    </request>

    <request name="destroy" type="destructor">
      <description summary="destroy the fifo interface">
        Informs the server that the client will no longer be using
        this protocol object.

        Surface state changes previously made by this protocol are
        unaffected by this object's destruction.
      </description>
    </request>
  </interface>
</protocol>