predictor_jank_tracker.cc | Explore in Territory

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "cc/metrics/predictor_jank_tracker.h"
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <utility>
#include "base/metrics/histogram_macros.h"
#include "base/time/time.h"
#include "base/trace_event/trace_event.h"
#include "base/trace_event/typed_macros.h"
#include "base/tracing/protos/chrome_track_event.pbzero.h"

namespace cc {
namespace {

// We define an irregular sequence of screen displacement as an abrupt
// change in acceleration in a sequence of 3 frames, meaning that in
// a sequence of 3 frames acceleration should be ether positive or
// negative, and the sequence should either be increasing or decreasing
// but not both.
// for Example [1, 5, 10] and [10, 5, 1] are good screen displacement
// sequences but [1, 10, 5] is bad, because the acceleration between
// between the the first and second frame is 9, while between the second
// and third is -5, indicating an acceleration direction change.
// We conducted an experiment to find the ratio of the bigger to smaller
// displacement at which the human eye notices scrolling performance
// degradation, and the results were |d_large}/{d_small| > 1.4
// for less than 7 pixels of max displacement, and > 1.2 for more than 7.
// for more details please check the following document:
// http://doc/1Y0u0Tq5eUZff75nYUzQVw6JxmbZAW9m64pJidmnGWsY
constexpr float kScrollDeltaThreshold = …;
constexpr float kSlowJankyThreshold = …;
constexpr float kFastJankyThreshold = …;

float GetMaxDelta(float d1, float d2, float d3) { … }

std::pair<float, bool> GetJankyThresholdAndScrollSpeed(float d1,
                                                       float d2,
                                                       float d3) { … }

// To compare predictor performance for 3 consecutive frames, the
// frames have to been displaced in the same direction, otherwise
// comparasion can not occur.
bool VerifyFramesSameDirection(float& d1, float& d2, float& d3) { … }

}  // namespace

PredictorJankTracker::PredictorJankTracker() = default;
PredictorJankTracker::~PredictorJankTracker() = default;

float PredictorJankTracker::GetSlowScrollDeltaThreshold() { … }

float PredictorJankTracker::GetSlowScrollJankyThreshold() { … }

float PredictorJankTracker::GetFastScrollJankyThreshold() { … }

void PredictorJankTracker::ReportLatestScrollDelta(
    float next_delta,
    base::TimeTicks next_presentation_ts,
    base::TimeDelta vsync_interval,
    std::optional<EventMetrics::TraceId> trace_id) { … }

void PredictorJankTracker::ReportJankyFrame(
    float next_delta,
    float janky_value,
    bool contains_missed_vsyncs,
    bool slow_scroll,
    std::optional<EventMetrics::TraceId> trace_id) { … }

bool PredictorJankTracker::ContainsMissedVSync(
    base::TimeTicks& next_presentation_ts,
    base::TimeDelta& vsync_interval) { … }

void PredictorJankTracker::StoreLatestFrameData(
    float delta,
    base::TimeTicks presentation_ts,
    std::optional<EventMetrics::TraceId> trace_id) { … }

void PredictorJankTracker::ResetCurrentScrollReporting() { … }

void PredictorJankTracker::ReportJankyFramePercentage() { … }

}  // namespace cc
chromium/cc/metrics/predictor_jank_tracker.cc
