On Mon, 09 May 2016 11:48:07 -0500 Derek Foreman <[email protected]> wrote:
> On 09/05/16 06:45 AM, Pekka Paalanen 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. > > Was weston implemented with this assumption? I think I did, yes. But weston also has another bug: https://bugs.freedesktop.org/show_bug.cgi?id=94735 Weston needs fixing and verifying in any case. https://phabricator.freedesktop.org/T7359 > > 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. > > It would be really cool to have a test for this glitch in weston. :) Yeah, and I'd love to write that test, but we'll see when I can get to it and fixing weston. It will need to use screenshot-based testing, where the baseline test is racy (cursor may or may not be in the picture). > Anyway, > Reviewed-by: Derek Foreman <[email protected]> Thanks, pq > > 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 > > + applied. > > + > > + This request modifies the behaviour of wl_surface.commit request on > > + 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> > > > > >
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