On Sat, Apr 27, 2019 at 07:44:39AM +0000, Simon Ser wrote: > This commit makes it so a wl_output.done event is guaranteed to be sent with a > xdg_output.done event. > > This protocol change has been discussed in a recent xorg-devel discussions > [1]. > > First let's recap why a change is needed: Xwayland listens to both wl_output > and > xdg_output changes. When an output's properties change, Xwayland expects to > receive both a wl_output.done event and an xdg_output.done event. If that's > not > the case, Xwayland doesn't update its state (so old state is still exposed to > X11 clients). > > Most of the time, both objects will be updated at the same time (e.g. the > current mode is changed, so both wl_output.mode and xdg_output.logical_size > are > sent) so this won't be an issue. However in some situations only one of > wl_output or xdg_output changes. For instance: > > - The mode is changed at the same time as the scale, resulting in the same > logical_size. > - The compositor doesn't expose the outputs' position via wl_output, so > whenever > the position changes only xdg_output is updated. > > Both KDE [2] and wlroots [3] have experienced this issue. > > For this reason, I'd like to update the xdg-output protocol to make it > mandatory > to always send a wl_output.done event after xdg_output changes. This > effectively > makes wl_output.done atomically apply all output state (including the state of > add-on objects like xdg_output). This approach is pretty similar to > wl_surface.commit: this request will atomically apply surface state including > the state of e.g. the xdg_surface object tied to the wl_surface. > > To update the protocol to reflect this new requirement we can either: > > - **Bump xdg_output version**. The current protocol doesn't specify that > wl_output.done must be sent, adding this new requirement would be a breaking > change. We need to fix Xwayland for the current xdg_output version (maybe > make > it non-atomic for the current version, atomic for the new one?). Should we > deprecate xdg_output.done in the new version? > - **Don't bump xdg_output version**. This clarifies what is expected in > practice > by Xwayland, a major xdg_output consumer, and what is currently implemented > by > all compositors. > > There's one issue with the "don't bump" approach: indeed in practice > compositors > always send wl_output.done and xdg_output.done in pairs, however the ordering > between those two events is not guaranteed. This means some compositors might > send this sequence: > > wl_output.geometry(…) > wl_output.done() > xdg_output.logical_position(…) > xdg_output.done() > > In this case the wl_output.done event fails to atomically apply the xdg_output > state. > > For this reason, I think bumping the version is a better approach. > > This commit also deprecates xdg_output.done, which doesn't have any purpose > anymore.
Relying only on wl_output.done sounds good to me. Since the 'done' event here is eventally to go away, I think it'd be wise to state somewhere other than the 'done' documentation that the wl_output.done event is used to notify all changes have been communicated. Jonas (P.S. sorry for the ones in the To:/Cc: field for the multiple mails, for some reason mailman thinks I'm sending from my @redhat.com address, thus gets stuck on moderation. D.S.). > > [1]: https://lists.x.org/archives/xorg-devel/2019-April/058148.html > [2]: https://phabricator.kde.org/D19253 > [3]: https://github.com/swaywm/sway/issues/4064 > > Signed-off-by: Simon Ser <cont...@emersion.fr> > --- > unstable/xdg-output/xdg-output-unstable-v1.xml | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/unstable/xdg-output/xdg-output-unstable-v1.xml > b/unstable/xdg-output/xdg-output-unstable-v1.xml > index ccbfe1c..01ac7a7 100644 > --- a/unstable/xdg-output/xdg-output-unstable-v1.xml > +++ b/unstable/xdg-output/xdg-output-unstable-v1.xml > @@ -54,7 +54,7 @@ > reset. > </description> > > - <interface name="zxdg_output_manager_v1" version="2"> > + <interface name="zxdg_output_manager_v1" version="3"> > <description summary="manage xdg_output objects"> > A global factory interface for xdg_output objects. > </description> > @@ -77,7 +77,7 @@ > </request> > </interface> > > - <interface name="zxdg_output_v1" version="2"> > + <interface name="zxdg_output_v1" version="3"> > <description summary="compositor logical output region"> > An xdg_output describes part of the compositor geometry. > > @@ -157,6 +157,10 @@ > > This allows changes to the xdg_output properties to be seen as > atomic, even if they happen via multiple events. > + > + For objects version 3 onwards, this event is deprecated. Compositors > + are not required to send it anymore and must send wl_output.done > + instead. > </description> > </event> > > -- > 2.21.0 > > > _______________________________________________ > wayland-devel mailing list > wayland-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/wayland-devel _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/wayland-devel