[PATCH wayland] protocol: Clarify semantics of sub-surface placement requests

[Jonas Ådahl]

Clarify some semantics of wl_subsurface.place_below and
wl_subsurface.place_below that were not specified.

Signed-off-by: Jonas Ådahl <jadahl at gmail.com>
---

Hi,

Implementing support for sub-surfaces in mutter we ran in to some
unspecified behaviour in the subsurface placement protocol.

I have documented what I understand is how the implementation in weston
works (please correct me if I'm wrong). Is this the intended semantics?

Jonas

 protocol/wayland.xml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index 61fde84..619567c 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -1952,6 +1952,12 @@
 
 	A new sub-surface is initially added as the top-most in the stack
 	of its siblings and parent.
+
+	Between two sub-surface parent commits, the stacking of surfaces in a
+	sub-surface tree are executed as operations in the same order as the
+	requests were made. A placement request may alter two surfaces relative
+	placement by placing itself in-between. A subsequent placement request
+	to a sub-surface replaces any previous requests.
       </description>
 
       <arg name="sibling" type="object" interface="wl_surface"
-- 
1.8.3.2