1 // Copyright 2019 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "third_party/blink/renderer/platform/widget/input/momentum_scroll_jank_tracker.h"
6
7 #include "base/metrics/histogram_functions.h"
8 #include "third_party/blink/renderer/platform/widget/input/event_with_callback.h"
9
10 namespace blink {
11
12 constexpr base::TimeDelta MomentumScrollJankTracker::kRecentEventCutoff;
13
~MomentumScrollJankTracker()14 MomentumScrollJankTracker::~MomentumScrollJankTracker() {
15 // Don't log if this scroll had no momentum input (after the first event).
16 if (total_event_count_ == 0)
17 return;
18
19 // We want to target 0 janks, so round our percentages up so that a single
20 // jank over a large number of frames doesn't get lost.
21 // Don't worry about overflow as we'd need a gesture > 100hrs long to hit,
22 // and the downside is an incorrect metric.
23 uint32_t rounding_factor = total_event_count_ - 1;
24 uint32_t jank_percentage =
25 (jank_count_ * 100 + rounding_factor) / total_event_count_;
26
27 base::UmaHistogramPercentageObsoleteDoNotUse(
28 "Renderer4.MomentumScrollJankPercentage", jank_percentage);
29 }
30
OnDispatchedInputEvent(EventWithCallback * event_with_callback,const base::TimeTicks & now)31 void MomentumScrollJankTracker::OnDispatchedInputEvent(
32 EventWithCallback* event_with_callback,
33 const base::TimeTicks& now) {
34 DCHECK_EQ(event_with_callback->event().GetType(),
35 WebGestureEvent::Type::kGestureScrollUpdate);
36
37 const auto& gesture_event =
38 static_cast<const WebGestureEvent&>(event_with_callback->event());
39
40 // If the scroll is not in the momentum phase, it's driven by user input,
41 // which happens at a higher frequency. Ignore this.
42 if (gesture_event.data.scroll_update.inertial_phase !=
43 WebGestureEvent::InertialPhaseState::kMomentum) {
44 return;
45 }
46
47 // Ignore the first momentum input event, as this may happen out-of band
48 // with BeginFrame, and may be coalesced in a non-jank scenario.
49 // TODO(ericrk): Add a metric to track jank in the transition from user
50 // to momentum input.
51 if (!seen_first_momentum_input_) {
52 seen_first_momentum_input_ = true;
53 return;
54 }
55
56 total_event_count_ += event_with_callback->coalesced_count();
57
58 jank_count_ +=
59 event_with_callback->coalesced_count() - kExpectedMomentumEventsPerFrame;
60 }
61
62 } // namespace blink
63