On Fri, Jul 12, 2019 at 03:42:52PM +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. > > [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 <[email protected]> > Reviewed-by: Olivier Fourdan <[email protected]>
Lets go with this! Reviewed-by: Jonas Ådahl <[email protected]> Jonas > --- > > Changes from v2 to v3: in xdg_output's description, mention wl_output.done is > guaranteed to be sent only from version 3. > > unstable/xdg-output/xdg-output-unstable-v1.xml | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/unstable/xdg-output/xdg-output-unstable-v1.xml > b/unstable/xdg-output/xdg-output-unstable-v1.xml > index ccbfe1c9a955..9efb7a40417b 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> > @@ -77,12 +77,17 @@ > </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. > > This typically corresponds to a monitor that displays part of the > compositor space. > + > + For objects version 3 onwards, after all xdg_output properties have > been > + sent (when the object is created and when properties are updated), a > + wl_output.done event is sent. This allows changes to the output > + properties to be seen as atomic, even if they happen via multiple > events. > </description> > > <request name="destroy" type="destructor"> > @@ -157,6 +162,10 @@ > > 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> > > -- > 2.22.0 > > > _______________________________________________ > 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
