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// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'percentile_utils.dart';
import 'timeline.dart';
/// Key for SceneDisplayLag timeline events.
const String kSceneDisplayLagEvent = 'SceneDisplayLag';
const String _kVsyncTransitionsMissed = 'vsync_transitions_missed';
/// Summarizes [TimelineEvents]s corresponding to [kSceneDisplayLagEvent] events.
///
/// A sample event (some fields have been omitted for brevity):
/// ```
/// {
/// "name": "SceneDisplayLag",
/// "ts": 408920509340,
/// "ph": "b", (this can be 'b' or 'e' for begin or end)
/// "args": {
/// "frame_target_time": "408920509340458",
/// "current_frame_target_time": "408920542689291",
/// "vsync_transitions_missed": "2"
/// }
/// },
/// ```
///
/// `vsync_transitions_missed` corresponds to the elapsed number of frame budget
/// durations between when the frame was scheduled to be displayed, i.e, the
/// `frame_target_time` and the next vsync pulse timestamp, i.e, the
/// `current_frame_target_time`.
class SceneDisplayLagSummarizer {
/// Creates a SceneDisplayLagSummarizer given the timeline events.
SceneDisplayLagSummarizer(this.sceneDisplayLagEvents) {
for (final TimelineEvent event in sceneDisplayLagEvents) {
assert(event.name == kSceneDisplayLagEvent);
}
}
/// The scene display lag events.
final List<TimelineEvent> sceneDisplayLagEvents;
/// Computes the average of the `vsync_transitions_missed` over the lag events.
double computeAverageVsyncTransitionsMissed() {
if (sceneDisplayLagEvents.isEmpty) {
return 0;
}
final double total = sceneDisplayLagEvents
.map(_getVsyncTransitionsMissed)
.reduce((double a, double b) => a + b);
return total / sceneDisplayLagEvents.length;
}
/// The [percentile]-th percentile `vsync_transitions_missed` over the lag events.
double computePercentileVsyncTransitionsMissed(double percentile) {
if (sceneDisplayLagEvents.isEmpty) {
return 0;
}
final List<double> doubles =
sceneDisplayLagEvents.map(_getVsyncTransitionsMissed).toList();
return findPercentile(doubles, percentile);
}
double _getVsyncTransitionsMissed(TimelineEvent e) {
assert(e.name == kSceneDisplayLagEvent);
assert(e.arguments!.containsKey(_kVsyncTransitionsMissed));
final dynamic transitionsMissed = e.arguments![_kVsyncTransitionsMissed];
assert(transitionsMissed is String);
return double.parse(transitionsMissed as String);
}
}