1 // Copyright 2019 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef CC_METRICS_AVERAGE_LAG_TRACKER_H_
6 #define CC_METRICS_AVERAGE_LAG_TRACKER_H_
11 #include "base/time/time.h"
12 #include "cc/cc_export.h"
16 // A class for reporting AverageLag metrics. See
17 // https://docs.google.com/document/d/1e8NuzPblIv2B9bz01oSj40rmlse7_PHq5oFS3lqz6N4/
18 class CC_EXPORT AverageLagTracker {
20 enum class EventType { ScrollBegin, ScrollUpdate };
23 EventInfo(float event_scroll_delta,
24 float predicted_scroll_delta,
25 base::TimeTicks event_timestamp,
27 : event_scroll_delta(event_scroll_delta),
28 predicted_scroll_delta(predicted_scroll_delta),
29 event_timestamp(event_timestamp),
30 event_type(event_type) {}
31 // Delta reported by the scroll event (begin or update).
32 float event_scroll_delta;
33 // Delta predicted (when prediction is on, otherwise should be equals to
34 // |event_scroll_delta|).
35 float predicted_scroll_delta;
36 // Timestamp when the scroll event happened.
37 base::TimeTicks event_timestamp;
38 // Timestamp when the scroll event's frame finished, which is currently
39 // when the frame swap completed.
40 base::TimeTicks finish_timestamp;
41 // Scroll event type (begin or update).
48 // Disallow copy and assign.
49 AverageLagTracker(const AverageLagTracker&) = delete;
50 AverageLagTracker& operator=(AverageLagTracker const&) = delete;
52 // Adds a scroll event defined by |event_info|.
53 void AddScrollEventInFrame(const EventInfo& event_info);
56 std::string GetAverageLagMetricName(EventType) const;
59 struct LagAreaInFrame {
60 explicit LagAreaInFrame(base::TimeTicks time,
61 float rendered_pos = 0,
62 float rendered_pos_no_prediction = 0)
64 rendered_accumulated_delta(rendered_pos),
66 rendered_accumulated_delta_no_prediction(rendered_pos_no_prediction),
67 lag_area_no_prediction(0) {}
68 base::TimeTicks frame_time;
69 // |rendered_accumulated_delta| is the cumulative delta that was swapped for
70 // this frame; this is based on the predicted delta, if prediction is
72 float rendered_accumulated_delta;
73 // |lag_area| is computed once a future input is processed that occurs after
74 // the swap timestamp (so that we can compute how far the rendered delta
75 // was from the actual position at the swap time).
77 // |rendered_accumulated_delta_no_prediction| is the what would have been
78 // rendered if prediction was not taken into account, i.e., the actual delta
79 // from the input event.
80 float rendered_accumulated_delta_no_prediction;
81 // |lag_area_no_prediction| is computed the same as |lag_area| but using
82 // rendered_accumulated_delta_no_prediction as the rendered delta.
83 float lag_area_no_prediction;
86 // Processes |event_info| as a ScrollBegin event and add it to the Lag.
87 void AddScrollBeginInFrame(const EventInfo& event_info);
88 // Processes |event_info| as a ScrollUpdate event and add it to the Lag.
89 void AddScrollUpdateInFrame(const EventInfo& event_info);
91 // Calculate lag in 1 seconds intervals and report UMA.
92 void CalculateAndReportAverageLagUma(bool send_anyway = false);
94 // Helper function to calculate lag area between |front_time| to
96 float LagBetween(base::TimeTicks front_time,
97 base::TimeTicks back_time,
99 base::TimeTicks event_time,
100 float rendered_accumulated_delta);
102 float LagForUnfinishedFrame(float rendered_accumulated_delta);
104 std::deque<LagAreaInFrame> frame_lag_infos_;
106 // Last scroll event's timestamp in the sequence, reset on ScrollBegin.
107 base::TimeTicks last_event_timestamp_;
108 // Timestamp of the last frame popped from |frame_lag_infos_| queue.
109 base::TimeTicks last_finished_frame_time_;
111 // Accumulated scroll delta for actual scroll update events. Cumulated from
112 // event_scroll_delta. Reset on ScrollBegin.
113 float last_event_accumulated_delta_ = 0;
114 // Accumulated scroll delta got rendered on gpu swap. Cumulated from
115 // predicted_scroll_delta. It always has same value as
116 // |last_event_accumulated_delta_| when scroll prediction is disabled.
117 float last_rendered_accumulated_delta_ = 0;
119 // This keeps track of the last report_time when we report to UMA, so we can
120 // calculate the report's duration by current - last. Reset on ScrollBegin.
121 base::TimeTicks last_reported_time_;
123 // True if the first element of |frame_lag_infos_| is for ScrollBegin.
124 // For ScrollBegin, we don't wait for the 1 second interval but record the
125 // UMA once the frame is finished.
126 bool is_begin_ = false;
128 // Accumulated lag area in the 1 second intervals.
129 float accumulated_lag_ = 0;
130 // Accumulated lag not taking into account the predicted deltas.
131 float accumulated_lag_no_prediction_ = 0;
136 #endif // CC_METRICS_AVERAGE_LAG_TRACKER_H_