ui/base/prediction/linear_resampling.h

// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_BASE_PREDICTION_LINEAR_RESAMPLING_H_
#define UI_BASE_PREDICTION_LINEAR_RESAMPLING_H_

#include <deque>

#include "base/component_export.h"
#include "ui/base/prediction/input_predictor.h"

namespace ui {

// This class use linear extrapolates / interpolates to resample events to
// frame_time - kResampleLatency. This resampling logic is to match the
// resampling behavior on Android. It's not designed for pointerevent's
// PredictedEvent and should not be used for that purpose.
// Resampling on Android see:
// https://android.googlesource.com/platform/frameworks/native/+/master/libs/input/InputTransport.cpp
class COMPONENT_EXPORT(UI_BASE_PREDICTION) LinearResampling
    : public InputPredictor {
 public:
  explicit LinearResampling();
  ~LinearResampling() override;

  const char* GetName() const override;

  // Reset the predictor to initial state.
  void Reset() override;

  // Store current input in queue.
  void Update(const InputData& new_input) override;

  // Return if there is enough data in the queue to generate prediction.
  bool HasPrediction() const override;

  // Generate the prediction based on stored points and given frame_time.
  // Return false if no prediction available.
  std::unique_ptr<InputData> GeneratePrediction(
      base::TimeTicks frame_time) const override;

  // Return the average time delta in the event queue.
  base::TimeDelta TimeInterval() const override;

 private:
  static constexpr size_t kNumEventsForResampling = 2;

  // Store the last events received
  std::deque<InputData> events_queue_;

  // Store the current delta time between the last 2 events
  base::TimeDelta events_dt_;

  DISALLOW_COPY_AND_ASSIGN(LinearResampling);
};

}  // namespace ui

#endif  // UI_BASE_PREDICTION_LINEAR_RESAMPLING_H_