ui/events/gestures/physics_based_fling_curve.h

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

#ifndef UI_EVENTS_GESTURES_PHYSICS_BASED_FLING_CURVE_H_
#define UI_EVENTS_GESTURES_PHYSICS_BASED_FLING_CURVE_H_

#include "base/time/time.h"
#include "ui/events/events_base_export.h"
#include "ui/events/gesture_curve.h"
#include "ui/gfx/geometry/cubic_bezier.h"
#include "ui/gfx/geometry/point_f.h"
#include "ui/gfx/geometry/size.h"
#include "ui/gfx/geometry/vector2d_f.h"

namespace ui {

// PhysicsBasedFlingCurve generates animation curve, similar to
// DirectManipulation's fling curve that can be used to scroll a UI element
// suitable for touch screen-based flings.
class EVENTS_BASE_EXPORT PhysicsBasedFlingCurve : public GestureCurve {
 public:
  PhysicsBasedFlingCurve(
      const gfx::Vector2dF& velocity,
      base::TimeTicks start_timestamp,
      const gfx::Vector2dF& pixels_per_inch,
      // Multiplier for fling distance based on fling boosting
      const float boost_multiplier,
      // Maximum fling distance subject to boost_multiplier and default
      // bounds multiplier
      const gfx::Size& bounding_size);

  PhysicsBasedFlingCurve(const PhysicsBasedFlingCurve&) = delete;
  PhysicsBasedFlingCurve& operator=(const PhysicsBasedFlingCurve&) = delete;

  ~PhysicsBasedFlingCurve() override;

  // GestureCurve implementation.
  bool ComputeScrollOffset(base::TimeTicks time,
                           gfx::Vector2dF* offset,
                           gfx::Vector2dF* velocity) override;

  // TODO(crbug.com/1028501): Use base::TimeDelta for curve_duration()
  // once crrev.com/c/1865928 is merged.
  float curve_duration() const { return curve_duration_.InSecondsF(); }
  const gfx::PointF& p1_for_testing() const { return p1_; }
  const gfx::PointF& p2_for_testing() const { return p2_; }
  static int default_bounds_multiplier_for_testing() {
    return kDefaultBoundsMultiplier;
  }

 private:
  // Default value used to scale the viewport when it is passed in as a
  // parameter in the generation of a physics based fling curve. This value
  // increases the upper bound of the scroll distance for a fling.
  constexpr static int kDefaultBoundsMultiplier = 3;

  // Calculates the curve duration and generates the control points for a bezier
  // curve. The slope is based on the input initial |velocity|, calculated curve
  // duration, and |distance_|. Returns the duration.
  base::TimeDelta CalculateDurationAndConfigureControlPoints(
      const gfx::Vector2dF& velocity);

  // Time when fling curve is generated.
  const base::TimeTicks start_timestamp_;
  // Cubic bezier curve control points.
  gfx::PointF p1_;
  gfx::PointF p2_;
  // Distance it can scroll with input velocity.
  const gfx::Vector2dF distance_;
  // Time until which fling can remain active relative to |start_timestamp_|.
  const base::TimeDelta curve_duration_;

  const gfx::CubicBezier bezier_;
  base::TimeDelta previous_time_delta_;
  gfx::Vector2dF cumulative_scroll_;
  gfx::Vector2dF prev_offset_;
};

}  // namespace ui

#endif  // UI_EVENTS_GESTURES_PHYSICS_BASED_FLING_CURVE_H_