weston/protocol/subsurface.xml

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

  <copyright>
    Copyright © 2012-2013 Collabora, Ltd.

    Permission to use, copy, modify, distribute, and sell this
    software and its documentation for any purpose is hereby granted
    without fee, provided that the above copyright notice appear in
    all copies and that both that copyright notice and this permission
    notice appear in supporting documentation, and that the name of
    the copyright holders not be used in advertising or publicity
    pertaining to distribution of the software without specific,
    written prior permission.  The copyright holders make no
    representations about the suitability of this software for any
    purpose.  It is provided "as is" without express or implied
    warranty.

    THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS
    SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
    FITNESS, IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY
    SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
    AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
    ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
    THIS SOFTWARE.
  </copyright>

  <interface name="wl_subcompositor" version="1">
    <description summary="sub-surface compositing">
      The global interface exposing sub-surface compositing capabilities.
      A wl_surface, that has sub-surfaces associated, is called the
      parent surface. Sub-surfaces can be arbitrarily nested and create
      a tree of sub-surfaces.

      The root surface in a tree of sub-surfaces is the main
      surface. The main surface cannot be a sub-surface, because
      sub-surfaces must always have a parent.

      A main surface with its sub-surfaces forms a (compound) window.
      For window management purposes, this set of wl_surface objects is
      to be considered as a single window, and it should also behave as
      such.

      The aim of sub-surfaces is to offload some of the compositing work
      within a window from clients to the compositor. A prime example is
      a video player with decorations and video in separate wl_surface
      objects. This should allow the compositor to pass YUV video buffer
      processing to dedicated overlay hardware when possible.
    </description>

    <request name="destroy" type="destructor">
      <description summary="unbind from the subcompositor interface">
	Informs the server that the client will not be using this
	protocol object anymore. This does not affect any other
	objects, wl_subsurface objects included.
      </description>
    </request>

    <enum name="error">
      <entry name="bad_surface" value="0"
             summary="the to-be sub-surface is invalid"/>
      <entry name="bad_parent" value="1"
             summary="the given parent is a sub-surface"/>
    </enum>

    <request name="get_subsurface">
      <description summary="give a surface the role sub-surface">
	Create a sub-surface interface for the given surface, and
	associate it with the given parent surface. This turns a
	plain wl_surface into a sub-surface.

	The to-be sub-surface must not already have a dedicated
	purpose, like any shell surface type, cursor image, drag icon,
	or sub-surface. Otherwise a protocol error is raised.
      </description>

      <arg name="id" type="new_id" interface="wl_subsurface"
           summary="the new subsurface object id"/>
      <arg name="surface" type="object" interface="wl_surface"
           summary="the surface to be turned into a sub-surface"/>
      <arg name="parent" type="object" interface="wl_surface"
           summary="the parent surface"/>
    </request>
  </interface>

  <interface name="wl_subsurface" version="1">
    <description summary="sub-surface interface to a wl_surface">
      An additional interface to a wl_surface object, which has been
      made a sub-surface. A sub-surface has one parent surface.

      A sub-surface becomes mapped, when a non-NULL wl_buffer is applied
      and the parent surface is mapped. The order of which one happens
      first is irrelevant. A sub-surface is hidden if the parent becomes
      hidden, or if a NULL wl_buffer is applied. These rules apply
      recursively through the tree of surfaces.

      The behaviour of wl_surface.commit request on a sub-surface
      depends on the sub-surface's mode. The possible modes are
      synchronized and desynchronized, see methods
      wl_subsurface.set_sync and wl_subsurface.set_desync. Synchronized
      mode caches wl_surface state to be applied on the next parent
      surface's commit, and desynchronized mode applies the pending
      wl_surface state directly. A sub-surface is initially in the
      synchronized mode.

      Sub-surfaces have also other kind of state, which is managed by
      wl_subsurface requests, as opposed to wl_surface requests. This
      state includes the sub-surface position relative to the parent
      surface (wl_subsurface.set_position), and the stacking order of
      the parent and its sub-surfaces (wl_subsurface.place_above and
      .place_below). This state is applied when the parent surface's
      wl_surface state is applied, regardless of the sub-surface's mode.
      As the exception, set_sync and set_desync are effective immediately.

      The main surface can thought to be always in desynchronized mode,
      since it does not have a parent in the sub-surfaces sense.

      Even if a sub-surface is in desynchronized mode, it will behave as
      in synchronized mode, if its parent surface behaves as in
      synchronized mode. This rule is applied recursively throughout the
      tree of surfaces. This means, that one can set a sub-surface into
      synchronized mode, and then assume that all its child sub-surfaces
      are synchronized, too, without explicitly setting them.

      If the wl_surface associated with the wl_subsurface is destroyed, the
      wl_subsurface object becomes inert. Note, that destroying either object
      takes effect immediately. If you need to synchronize the removal
      of a sub-surface to the parent surface update, unmap the sub-surface
      first by attaching a NULL wl_buffer, update parent, and then destroy
      the sub-surface.

      If the parent wl_surface object is destroyed, the sub-surface is
      unmapped.
    </description>

    <request name="destroy" type="destructor">
      <description summary="remove sub-surface interface">
	The sub-surface interface is removed from the wl_surface object
	that was turned into a sub-surface with
	wl_subcompositor.get_subsurface request. The wl_surface's association
	to the parent is deleted, and the wl_surface loses its role as
	a sub-surface. The wl_surface is unmapped.
      </description>
    </request>

    <enum name="error">
      <entry name="bad_surface" value="0"
             summary="wl_surface is not a sibling or the parent"/>
    </enum>

    <request name="set_position">
      <description summary="reposition the sub-surface">
	This schedules a sub-surface position change.
	The sub-surface will be moved so, that its origin (top-left
	corner pixel) will be at the location x, y of the parent surface.

	The next wl_surface.commit on the parent surface will reset
	the sub-surface's position to the scheduled coordinates.

	The initial position is 0, 0.
      </description>

      <arg name="x" type="int" summary="coordinate in the parent surface"/>
      <arg name="y" type="int" summary="coordinate in the parent surface"/>
    </request>

    <request name="place_above">
      <description summary="restack the sub-surface">
	This sub-surface is taken from the stack, and put back just
	above the reference surface, changing the z-order of the sub-surfaces.
	The reference surface must be one of the sibling surfaces, or the
	parent surface. Using any other surface, including this sub-surface,
	will cause a protocol error.

	The z-order is double-buffered state, and will be applied on the
	next commit of the parent surface.
	See wl_surface.commit and wl_subcompositor.get_subsurface.
      </description>

      <arg name="sibling" type="object" interface="wl_surface"
           summary="the reference surface"/>
    </request>

    <request name="place_below">
      <description summary="restack the sub-surface">
	The sub-surface is placed just below of the reference surface.
	See wl_subsurface.place_above.
      </description>

      <arg name="sibling" type="object" interface="wl_surface"
           summary="the reference surface"/>
    </request>

    <request name="set_sync">
      <description summary="set sub-surface to synchronized mode">
	Change the commit behaviour of the sub-surface to synchronized
	mode, also described as the parent dependant mode.

	In synchronized mode, wl_surface.commit on a sub-surface will
	accumulate the committed state in a cache, but the state will
	not be applied and hence will not change the compositor output.
	The cached state is applied to the sub-surface when
	wl_surface.commit is called on the parent surface, after the
	parent surface's own state is applied. This ensures atomic
	updates of the parent and all its synchronized sub-surfaces.
	Applying the cached state will invalidate the cache, so further
	parent surface commits do not (re-)apply old state.

	See wl_subsurface for the recursive effect of this mode.
      </description>
    </request>

    <request name="set_desync">
      <description summary="set sub-surface to desynchronized mode">
	Change the commit behaviour of the sub-surface to desynchronized
	mode, also described as independent or freely running mode.

	In desynchronized mode, wl_surface.commit on a sub-surface will
	apply the pending state directly, without caching, as happens
	normally with a wl_surface. Calling wl_surface.commit on the
	parent surface has no effect on the sub-surface's wl_surface
	state. This mode allows a sub-surface to be updated on its own.

	If cached state exists when wl_surface.commit is called in
	desynchronized mode, the pending state is added to the cached
	state, and applied as whole. This invalidates the cache.

	Note: even if a sub-surface is set to desynchronized, a parent
	sub-surface may override it to behave as synchronized. For details,
	see wl_subsurface.
      </description>
    </request>

  </interface>
</protocol>