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// Copyright 2018 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.
#include <deque>
#include <vector>
#include "base/component_export.h"
#include "ui/base/prediction/input_predictor.h"
#include "ui/base/prediction/kalman_filter.h"
namespace ui {
// Class to perform kalman filter prediction inherited from InputPredictor.
// This predictor uses kalman filters to predict the current status of the
// motion. Then it predict the future points using <current_position,
// predicted_velocity, predicted_acceleration>. Each kalman_filter will only
// be used to predict one dimension (x, y).
: public InputPredictor {
// Heuristic option enables changing the influence of acceleration based on
// change of direction. Direction cut off enables discarding the prediction if
// the predicted direction is opposite from the current direction.
enum PredictionOptions {
kNone = 0x0,
kHeuristicsEnabled = 0x1,
kDirectionCutOffEnabled = 0x2
explicit KalmanPredictor(unsigned int prediction_options);
~KalmanPredictor() override;
const char* GetName() const override;
// Reset the predictor to initial state.
void Reset() override;
// Store current input in queue.
void Update(const InputData& cur_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 time_stamp.
// Return false if no prediction available.
std::unique_ptr<InputData> GeneratePrediction(
base::TimeTicks predict_time) const override;
// Return the filtered value of time intervals.
base::TimeDelta TimeInterval() const override;
// The following functions get the predicted values from kalman filters.
gfx::Vector2dF PredictPosition() const;
gfx::Vector2dF PredictVelocity() const;
gfx::Vector2dF PredictAcceleration() const;
// Predictor for each axis.
KalmanFilter x_predictor_;
KalmanFilter y_predictor_;
// Filter to smooth time intervals.
KalmanFilter time_filter_;
// Most recent input data.
std::deque<InputData> last_points_;
// Maximum time interval between first and last events in last points queue.
static constexpr base::TimeDelta kMaxTimeInQueue =
// Flags to determine the enabled prediction options.
const unsigned int prediction_options_;
} // namespace ui