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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 "base/basictypes.h"
#include "base/memory/scoped_ptr.h"
#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.
LSQ2,
// 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.
// 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.
STRATEGY_DEFAULT = LSQ2,
};
// Creates a velocity tracker using the default strategy for the platform.
VelocityTracker();
// Creates a velocity tracker using the specified strategy.
// If strategy is NULL, uses the default strategy for the platform.
explicit VelocityTracker(Strategy strategy);
~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 and clears the estimator if there is no information available
// about the pointer.
bool GetEstimator(uint32_t id, Estimator* out_estimator) const;
base::TimeTicks last_event_time_;
BitSet32 current_pointer_id_bits_;
int32_t active_pointer_id_;
scoped_ptr<VelocityTrackerStrategy> strategy_;
DISALLOW_COPY_AND_ASSIGN(VelocityTracker);
};
} // namespace ui
#endif // UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_H_
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