diff options
authorPekka Paalanen <>2013-11-15 16:09:45 +0200
committerKristian Høgsberg <>2013-11-15 20:49:36 -0800
commit81c57614d11787c00b8859cbaef650e284b4f188 (patch)
parent4a196570a3f528e9092014f8320f4a2bb4aba680 (diff)
protocol: add sub-surfaces to the core
The sub-surface protocol was originally committed into Weston on May 10th, 2013, in commit 2396aec6842c709a714f3825dbad9fd88478f2e6. The design for the protocol had started in the beginning of December 2012. I think it is high time to move this into the core now. This patch copies the sub-surface protocol as it was in Weston on Nov 15th, 2013, into Wayland. Weston gets a patch to remove the protocol from there. Sub-surface is a wl_surface role. You create a wl_surface as usual, and assign it the sub-surface role and a parent wl_surface. Sub-surfaces are an integral part of the parent surface, and stay glued to the parent. For window management, a window is the union of the top-level wl_surface and all its sub-surfaces. Sub-surfaces are not clipped to the parent, and the union of the surface tree can be larger than the (top-level) wl_surface at its root. The representative use case for sub-surfaces is a video player window. When the video content is given its own wl_surface, there is no need to modify the video frame contents after decoding or copy them into a whole window sized buffer before submitting it to the compositor. This allows efficient, zero-copy video presentation paths, where video decoding hardware produces a (YUV) buffer, which eventually ends up in a (YUV-capable) hardware overlay and is scanned out directly. This can also be used for zero-copy presentation of windowed OpenGL content, where the OpenGL rendering engine does not need to draw or avoid window decorations. Sub-surfaces allow mixing different buffer types into the same window, e.g. software-rendered decorations in wl_shm buffers, and live content in EGL-based buffers. However, the sub-surface extension does not offer clipping or scaling facilities, or accurate presentation timing. Those are topics for additional extensions. Signed-off-by: Pekka Paalanen <>
1 files changed, 217 insertions, 0 deletions
diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index a1df007..61fde84 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -4,6 +4,7 @@
Copyright © 2008-2011 Kristian Høgsberg
Copyright © 2010-2011 Intel Corporation
+ Copyright © 2012-2013 Collabora, Ltd.
Permission to use, copy, modify, distribute, and sell this
software and its documentation for any purpose is hereby granted
@@ -1795,4 +1796,220 @@
+ <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"/>
+ </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's size and position are not limited to that of the parent.
+ Particularly, a sub-surface is not automatically clipped to its
+ parent's area.
+ 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 the wl_surface state to be applied when the parent's
+ state gets applied, 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 be 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 and grand-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
+ coordinate system. The coordinates are not restricted to the parent
+ surface area. Negative values are allowed.
+ 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.
+ A new sub-surface is initially added as the top-most in the stack
+ of its siblings and parent.
+ </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 immediately after
+ the parent surface's 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.
+ If a surface's parent surface behaves as desynchronized, then
+ the cached state is applied on set_desync.
+ </description>
+ </request>
+ </interface>