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- // Copyright 2014 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_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_
- #define UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_
- #include <stdint.h>
- #include <memory>
- #include "base/time/time.h"
- #include "ui/events/gesture_detection/bitset_32.h"
- namespace ui {
- class MotionEvent;
- class VelocityTrackerStrategy;
- namespace {
- struct Estimator;
- struct Position;
- }
- // Port of VelocityTracker from Android
- // * platform/frameworks/native/include/input/VelocityTracker.h
- // * Change-Id: I4983db61b53e28479fc90d9211fafff68f7f49a6
- // * Please update the Change-Id as upstream Android changes are pulled.
- class VelocityTracker {
- public:
- enum {
- // The maximum number of pointers to use when computing the velocity.
- // Note that the supplied MotionEvent may expose more than 16 pointers, but
- // at most |MAX_POINTERS| will be used.
- MAX_POINTERS = 16,
- };
- enum Strategy {
- // 1st order least squares. Quality: POOR.
- // Frequently underfits the touch data especially when the finger
- // accelerates or changes direction. Often underestimates velocity. The
- // direction is overly influenced by historical touch points.
- LSQ1,
- // 2nd order least squares. Quality: VERY GOOD.
- // Pretty much ideal, but can be confused by certain kinds of touch data,
- // particularly if the panel has a tendency to generate delayed, duplicate
- // or jittery touch coordinates when the finger is released. This is the
- // default velocity tracker strategy. Although other strategies are
- // available for testing and comparison purposes, this is the strategy that
- // applications will actually use. Be very careful when adjusting the
- // default strategy because it can dramatically affect (often in a bad way)
- // the user experience.
- LSQ2,
- // The same as LSQ2, but reports 0 if the direction of the velocity returned
- // is sufficiently different from the primary direction of movement of the
- // touches contributing to the velocity.
- LSQ2_RESTRICTED,
- // 3rd order least squares. Quality: UNUSABLE.
- // Frequently overfits the touch data yielding wildly divergent estimates
- // of the velocity when the finger is released.
- LSQ3,
- // 2nd order weighted least squares, delta weighting.
- // Quality: EXPERIMENTAL
- WLSQ2_DELTA,
- // 2nd order weighted least squares, central weighting.
- // Quality: EXPERIMENTAL
- WLSQ2_CENTRAL,
- // 2nd order weighted least squares, recent weighting.
- // Quality: EXPERIMENTAL
- WLSQ2_RECENT,
- // 1st order integrating filter. Quality: GOOD.
- // Not as good as 'lsq2' because it cannot estimate acceleration but it is
- // more tolerant of errors. Like 'lsq1', this strategy tends to
- // underestimate
- // the velocity of a fling but this strategy tends to respond to changes in
- // direction more quickly and accurately.
- INT1,
- // 2nd order integrating filter. Quality: EXPERIMENTAL.
- // For comparison purposes only. Unlike 'int1' this strategy can compensate
- // for acceleration but it typically overestimates the effect.
- INT2,
- STRATEGY_MAX = INT2,
- // The default velocity tracker strategy.
- STRATEGY_DEFAULT = LSQ2,
- };
- // Creates a velocity tracker using the specified strategy.
- // If strategy is NULL, uses the default strategy for the platform.
- explicit VelocityTracker(Strategy strategy);
- VelocityTracker(const VelocityTracker&) = delete;
- VelocityTracker& operator=(const VelocityTracker&) = delete;
- ~VelocityTracker();
- // Resets the velocity tracker state.
- void Clear();
- // Adds movement information for all pointers in a MotionEvent, including
- // historical samples.
- void AddMovement(const MotionEvent& event);
- // Gets the velocity of the specified pointer id in position units per second.
- // Returns false and sets the velocity components to zero if there is
- // insufficient movement information for the pointer.
- bool GetVelocity(uint32_t id, float* outVx, float* outVy) const;
- // Gets the active pointer id, or -1 if none.
- inline int32_t GetActivePointerId() const { return active_pointer_id_; }
- // Gets a bitset containing all pointer ids from the most recent movement.
- inline BitSet32 GetCurrentPointerIdBits() const {
- return current_pointer_id_bits_;
- }
- private:
- // Resets the velocity tracker state for specific pointers.
- // Call this method when some pointers have changed and may be reusing
- // an id that was assigned to a different pointer earlier.
- void ClearPointers(BitSet32 id_bits);
- // Adds movement information for a set of pointers.
- // The id_bits bitfield specifies the pointer ids of the pointers whose
- // positions
- // are included in the movement.
- // The positions array contains position information for each pointer in order
- // by
- // increasing id. Its size should be equal to the number of one bits in
- // id_bits.
- void AddMovement(const base::TimeTicks& event_time,
- BitSet32 id_bits,
- const Position* positions);
- // Gets an estimator for the recent movements of the specified pointer id.
- // Returns false if the pointer velocity is unknown.
- bool GetEstimator(uint32_t id, Estimator* out_estimator) const;
- base::TimeTicks last_event_time_;
- BitSet32 current_pointer_id_bits_;
- int32_t active_pointer_id_;
- std::unique_ptr<VelocityTrackerStrategy> strategy_;
- };
- } // namespace ui
- #endif // UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_
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