<div dir="ltr">Hey, This came up during the mutter implementation. See my questions here for what prompted this. I found the proposed phrasing a bit confusing as well... <a href="https://bugzilla.gnome.org/show_bug.cgi?id=705502#c16">https://bugzilla.gnome.org/show_bug.cgi?id=705502#c16</a></div> <div class="gmail_extra"> <div class="gmail_quote">On Fri, Jan 17, 2014 at 6:37 AM, Jonas Ådahl <<a href="mailto:jadahl@gmail.com" target="_blank">jadahl@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <div class="HOEnZb"><div class="h5">On Fri, Jan 17, 2014 at 12:20:17PM +0200, Pekka Paalanen wrote: > Hi Jonas > > On Thu, 16 Jan 2014 23:27:07 +0100 > Jonas Ådahl <<a href="mailto:jadahl@gmail.com">jadahl@gmail.com</a>> wrote: > > > Clarify some semantics of wl_subsurface.place_below and > > wl_subsurface.place_below that were not specified. > > Below and below. ;-) > > > > > Signed-off-by: Jonas Ådahl <<a href="mailto:jadahl@gmail.com">jadahl@gmail.com</a>> > > --- > > > > 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" > > Hmm, I guess, but I am not sure I understand this description at all. > > The intention, and how the code works, is that each change is executed > in the order the place_above/below requests are sent, and each request > operates on the outcome of the previous. Whether there is a parent > commit in between or not makes no difference. > > The code has two lists: the effective ordering, and the pending > ordering. These requests directly affect the pending ordering as they > are received. When the parent surface is committed, the pending > ordering overwrites the effective ordering, making them equal. The > effective ordering is what is composited on screen. > > In essence, you can think of the place_above/below operating > immediately, and parent commits just publish the whole ordering. > > Does this help? Can you rephrase the protocol documentation? </div></div>This is how I understood it, but I'll try to rephrase it some, given your explanation, and send a v2. <div class="im"> > > What was the unspecified behaviour here? I'm not sure how else you > could understand place_above/below, but then again I'm the original > author so it's far too obvious to me. :-) </div>For example one could queue the operations until commit, having a subsequent request replace a previous one, instead of executing them immediately relying on commit to take a snapshot. It could also be read as a subsequent request that now replaces a previous request to be invalid. This should also be clarified in set_position so I'll send a patch for that too. Thanks for the review! Jonas <div class="HOEnZb"><div class="h5">_______________________________________________ wayland-devel mailing list <a href="mailto:wayland-devel@lists.freedesktop.org">wayland-devel@lists.freedesktop.org</a> <a href="http://lists.freedesktop.org/mailman/listinfo/wayland-devel" target="_blank">http://lists.freedesktop.org/mailman/listinfo/wayland-devel</a> </div></div></blockquote></div> -- Jasper </div>