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wayland: Remove unnecessary dispatch of frame callback source

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To avoid communicating lower frame rate to clients through frame
callbacks, it is important to avoid delaying the source dispatch when
a dispatch is already scheduled.

To that end, the previous logic would emit pending frame callbacks
immediately in case a source dispatch was still scheduled for the
previous refresh cycle and then (potentially) schedule another source
dispatch for the current refresh cycle.

However, emitting pending frame callbacks immediately would send
frame events for every pending frame callback, including for the
current "empty" update. Scheduling another source dispatch for the
current cycle was then unnecessary and potentially undesirable
because there may not even be another "empty" update during the cycle.

Instead, let the already-scheduled source dispatch handle emitting any
pending frame callbacks, and do not schedule an additional source
dispatch for the current cycle as it may not be needed.

This approach is useful because it removes an implicit assumption
that the refresh rate is fixed and that target presentation time
remains constant within a refresh cycle. This assumption does not
apply for VRR.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3521>
This commit is contained in:
Dor Askayo 2023-09-25 11:56:18 +03:00
parent 8c88dbfbe8
commit 26d8b9c69b
1 changed files with 3 additions and 10 deletions
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13
src/wayland/meta-wayland.c
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@ -97,7 +97,6 @@ typedef struct
MetaWaylandCompositor *compositor;
ClutterStageView *stage_view;
int64_t target_presentation_time_us;
} FrameCallbackSource;
static void meta_wayland_compositor_update_focus (MetaWaylandCompositor *compositor,
@ -295,7 +294,6 @@ on_after_update (ClutterStage *stage,
MetaContext *context = meta_wayland_compositor_get_context (compositor);
MetaBackend *backend = meta_context_get_backend (context);
MetaFrameNative *frame_native;
FrameCallbackSource *frame_callback_source;
GSource *source;
int64_t min_render_time_allowed_us;
int64_t target_presentation_time_us;
@ -309,7 +307,6 @@ on_after_update (ClutterStage *stage,
frame_native = meta_frame_native_from_frame (frame);
source = ensure_source_for_stage_view (compositor, stage_view);
frame_callback_source = (FrameCallbackSource *) source;
if (meta_frame_native_had_kms_update (frame_native) ||
!clutter_frame_get_min_render_time_allowed (frame,
@ -324,11 +321,6 @@ on_after_update (ClutterStage *stage,
{
int64_t frame_deadline_us;
if (g_source_get_ready_time (source) != -1 &&
frame_callback_source->target_presentation_time_us <
target_presentation_time_us)
emit_frame_callbacks_for_stage_view (compositor, stage_view);
frame_deadline_us = target_presentation_time_us -
min_render_time_allowed_us;
@ -339,8 +331,9 @@ on_after_update (ClutterStage *stage,
}
else
{
frame_callback_source->target_presentation_time_us =
target_presentation_time_us;
if (g_source_get_ready_time (source) != -1)
return;
g_source_set_ready_time (source, frame_deadline_us);
}
}