Hi Pekka, Two minor nits in the description, noted inline below. yong
On May 9, 2016, at 6:45 AM, Pekka Paalanen <[email protected]> wrote: > > From: Pekka Paalanen <[email protected]> > > The existing specification was not explicitly clear on when > wl_subcompositor.get_subsurface request actually adds the sub-surface to > the parent in the compositor's scenegraph. The implicit assumption was > that this happens immediately, but it was not written anywhere. > > If it happens immediately, the client doing things in a wrong order may > cause a glitch on screen. Particularly, if the wl_surface B that is > going to be a sub-surface for wl_surface A (the parent) already has a > buffer committed, and the parent surface is mapped, then get_subsurface > will (may?) cause wl_surface B to become mapped immediately. That leaves > no time to set up the sub-surface z-order or position before mapping, > hence there can be a visible glitch. > > The way to avoid that, given that the parent surface is mapped, is to > not commit a buffer to wl_surface B until all the sub-surface setup is > done. > > However, doing the sub-surface setup always requires a wl_surface.commit > on the parent surface unless the defaults happen to be correct. > > To make setting up a subsurface slightly easier by removing one > possibility for a glitch, this patch amends the specification to require > a wl_surface.commit on the parent surface for get_subsurface to > complete. The sub-surface cannot become mapped before a parent commit. > > This change may break existing clients that relied on the glitchy > sequence to not need a parent surface commit to map the sub-surface. > However, presumably all uses would at least issue a > wl_subsurface.set_position, which requires a parent surface commit to > apply. That would guarantee that there is a parent surface commit after > get_subsurface, and so reduces the chances of breaking anything. > > In other cases, this change may simply remove a possibility for the > glitch. > > This patch also adds a note about changing wl_surface.commit behaviour > on wl_subcompositor.get_subsurface. (That could be a separate patch.) > > The behaviour of wl_subsurface.destroy remains as specified, even though > it is now slightly asymmetrical to get_subsurface. This is emphasized by > adding the word "immediately". The effects of destruction were already > explicitly documented, as is the way to achieve synchronized unmapping, > so changing destruction behaviour would likely be more disruptive, and > also open up more corner cases (what would happen between destroy and > unmapping?). > > Bug: https://phabricator.freedesktop.org/T7358 > Cc: Martin Gräßlin <[email protected]> > Cc: Jonas Ådahl <[email protected]> > Cc: Chris Michael <[email protected]> > Signed-off-by: Pekka Paalanen <[email protected]> > --- > protocol/wayland.xml | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/protocol/wayland.xml b/protocol/wayland.xml > index 92e3f43..1546b46 100644 > --- a/protocol/wayland.xml > +++ b/protocol/wayland.xml > @@ -2487,6 +2487,14 @@ > The to-be sub-surface must not already have another role, and it > must not have an existing wl_subsurface object. Otherwise a protocol > error is raised. > + > + Adding sub-surfaces to a parent is a double-buffered operation on the > + parent (see wl_surface.commit). The effect of adding a sub-surface > + becomes visible on the next time the state of the parent surface is visible the next time > + applied. > + > + This request modifies the behaviour of wl_surface.commit request on requests > + the sub-surface, see the documentation on wl_subsurface interface. > </description> > > <arg name="id" type="new_id" interface="wl_subsurface" > @@ -2557,7 +2565,7 @@ > that was turned into a sub-surface with a > 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. > + a sub-surface. The wl_surface is unmapped immediately. > </description> > </request> > > -- > 2.7.3 > > _______________________________________________ > wayland-devel mailing list > [email protected] > https://lists.freedesktop.org/mailman/listinfo/wayland-devel _______________________________________________ wayland-devel mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/wayland-devel
