<?xml version="1.0" encoding="UTF-8"?>
<protocol name="xwayland_shell_v1">

  <copyright>
    Copyright © 2022 Joshua Ashton

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
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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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    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
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    DEALINGS IN THE SOFTWARE.
  </copyright>

  <description summary="Protocol for associating X11 windows to wl_surfaces">
    This protocol adds a xwayland_surface role which allows an Xwayland
    server to associate an X11 window to a wl_surface.
    
    Before this protocol, this would be done via the Xwayland server
    providing the wl_surface's resource id via the a client message with
    the WL_SURFACE_ID atom on the X window.
    This was problematic as a race could occur if the wl_surface
    associated with a WL_SURFACE_ID for a window was destroyed before the
    client message was processed by the compositor and another surface
    (or other object) had taken its id due to recycling.
    
    This protocol solves the problem by moving the X11 window to wl_surface
    association step to the Wayland side, which means that the association
    cannot happen out-of-sync with the resource lifetime of the wl_surface.
    
    This protocol avoids duplicating the race on the other side by adding a
    non-zero monotonic serial number which is entirely unique that is set on
    both the wl_surface (via. xwayland_surface_v1's set_serial method) and
    the X11 window (via. the `WL_SURFACE_SERIAL` client message) that can be
    used to associate them, and synchronize the two timelines.

    The key words "must", "must not", "required", "shall", "shall not",
    "should", "should not", "recommended",  "may", and "optional" in this
    document are to be interpreted as described in IETF RFC 2119.

    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>

  <interface name="xwayland_shell_v1" version="1">
    <description summary="context object for Xwayland shell">
      xwayland_shell_v1 is a singleton global object that
      provides the ability to create a xwayland_surface_v1 object
      for a given wl_surface.

      This interface is intended to be bound by the Xwayland server.

      A compositor must not allow clients other than Xwayland to
      bind to this interface. A compositor should hide this global
      from other clients' wl_registry.
      A client the compositor does not consider to be an Xwayland
      server attempting to bind this interface will result in
      an implementation-defined error.

      An Xwayland server that has bound this interface must not
      set the `WL_SURFACE_ID` atom on a window.
    </description>

    <enum name="error">
      <entry name="role" value="0" summary="given wl_surface has another role"/>
    </enum>

    <request name="destroy" type="destructor">
      <description summary="destroy the Xwayland shell object">
        Destroy the xwayland_shell_v1 object.

        The child objects created via this interface are unaffected.
      </description>
    </request>

    <request name="get_xwayland_surface">
      <description summary="assign the xwayland_surface surface role">
        Create an xwayland_surface_v1 interface for a given wl_surface
        object and gives it the xwayland_surface role.
        
        It is illegal to create an xwayland_surface_v1 for a wl_surface
        which already has an assigned role and this will result in the
        `role` protocol error.

        See the documentation of xwayland_surface_v1 for more details
        about what an xwayland_surface_v1 is and how it is used.
      </description>

      <arg name="id" type="new_id" interface="xwayland_surface_v1"/>
      <arg name="surface" type="object" interface="wl_surface"/>
    </request>
  </interface>

  <interface name="xwayland_surface_v1" version="1">
    <description summary="interface for associating Xwayland windows to wl_surfaces">
      An Xwayland surface is a surface managed by an Xwayland server.
      It is used for associating surfaces to Xwayland windows.

      The Xwayland server associated with actions in this interface is
      determined by the Wayland client making the request.

      The client must call wl_surface.commit on the corresponding wl_surface
      for the xwayland_surface_v1 state to take effect.
    </description>

    <enum name="error">
      <entry name="already_associated" value="0" summary="given wl_surface is already associated with an X11 window"/>
      <entry name="invalid_serial" value="1" summary="serial was not valid"/>
    </enum>

    <request name="set_serial">
      <description summary="associates a Xwayland window to a wl_surface">
        Associates an Xwayland window to a wl_surface.
        The association state is double-buffered, see wl_surface.commit.

        The `serial_lo` and `serial_hi` parameters specify a non-zero
        monotonic serial number which is entirely unique and provided by the
        Xwayland server equal to the serial value provided by a client message
        with a message type of the `WL_SURFACE_SERIAL` atom on the X11 window
        for this surface to be associated to.

        The serial value in the `WL_SURFACE_SERIAL` client message is specified
        as having the lo-bits specified in `l[0]` and the hi-bits specified
        in `l[1]`.

        If the serial value provided by `serial_lo` and `serial_hi` is not
        valid, the `invalid_serial` protocol error will be raised.

        An X11 window may be associated with multiple surfaces throughout its
        lifespan. (eg. unmapping and remapping a window).
        
        For each wl_surface, this state must not be committed more than once,
        otherwise the `already_associated` protocol error will be raised.
      </description>
      <arg name="serial_lo" type="uint" summary="The lower 32-bits of the serial number associated with the X11 window"/>
      <arg name="serial_hi" type="uint" summary="The upper 32-bits of the serial number associated with the X11 window"/>
    </request>

    <request name="destroy" type="destructor">
      <description summary="destroy the Xwayland surface object">
        Destroy the xwayland_surface_v1 object.

        Any already existing associations are unaffected by this action.
      </description>
    </request>
  </interface>
</protocol>