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compositor/x11: Sync again at the end of before_paint

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The existing comment tells us this is necessary:

> there may be drawing between the last damage event and the
> XDamageSubtract() that needs to be flushed as well.

But the commit message for 551101c65c also tells us that
synchronization is necessary before-update. Assuming both are correct
then it needs to be done in both places.

I did try optimizing out the second sync to only do it if damage
arrived during the update, but that doesn't seem to be the issue.
The damage event is arriving before the update starts and it's some
secondary changes within the damage region running late that need
flushing. So this means the client is reporting damage more frequently
than the frame rate and we're ignoring the secondary damage reports
for efficiency (XDamageReportBoundingBox), which is still a good thing.

Fixes: 551101c65c ("compositor-x11: Move synchronization to before-update")
Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/2880
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3590>
This commit is contained in:
Daniel van Vugt 2024-02-16 16:57:55 +08:00
parent cf9f7f427e
commit f606a4424a
1 changed files with 26 additions and 4 deletions
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30
src/compositor/meta-compositor-x11.c
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@ -325,10 +325,7 @@ out:
}
static void
on_before_update (ClutterStage *stage,
ClutterStageView *stage_view,
ClutterFrame *frame,
MetaCompositor *compositor)
maybe_do_sync (MetaCompositor *compositor)
{
MetaCompositorX11 *compositor_x11 = META_COMPOSITOR_X11 (compositor);
@ -363,6 +360,15 @@ on_before_update (ClutterStage *stage,
}
}
static void
on_before_update (ClutterStage *stage,
ClutterStageView *stage_view,
ClutterFrame *frame,
MetaCompositor *compositor)
{
maybe_do_sync (compositor);
}
static void
on_after_update (ClutterStage *stage,
ClutterStageView *stage_view,
@ -391,6 +397,22 @@ meta_compositor_x11_before_paint (MetaCompositor *compositor,
parent_class = META_COMPOSITOR_CLASS (meta_compositor_x11_parent_class);
parent_class->before_paint (compositor, compositor_view);
/* We must sync after MetaCompositor's before_paint because that's the final
* time XDamageSubtract may happen before painting (when it calls
* meta_window_actor_x11_before_paint -> handle_updates ->
* meta_surface_actor_x11_handle_updates). If a client was to redraw between
* the last damage event and XDamageSubtract, and the bounding box of the
* region didn't grow, then we will not receive a new damage report for it
* (because XDamageReportBoundingBox). Then if we haven't synchronized again
* and the same region doesn't change on subsequent frames, we have lost some
* part of the update from the client. So to ensure the correct pixels get
* composited we must sync at least once between XDamageSubtract and
* compositing, which is here. More related documentation can be found in
* maybe_do_sync.
*/
maybe_do_sync (compositor);
}
static void