text: // 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.
  
  #ifndef CC_INPUT_SNAP_FLING_CURVE_H_
  #define CC_INPUT_SNAP_FLING_CURVE_H_
  
  #include "base/time/time.h"
  #include "cc/cc_export.h"
  #include "ui/gfx/geometry/rect_f.h"
  #include "ui/gfx/geometry/vector2d_f.h"
  
  namespace cc {
  
  // The curve for the snap fling animation. The curve would generate a geometric
  // sequence of deltas to be scrolled at each frame.
  class CC_EXPORT SnapFlingCurve {
   public:
    // Creates the curve based on the start offset, target offset, and the first
    // inertial GSU's time_stamp.
    SnapFlingCurve(const gfx::PointF& start_offset,
                   const gfx::PointF& target_offset,
                   base::TimeTicks first_gsu_time);
  
    virtual ~SnapFlingCurve();
  
    // Estimate the total distance that will be scrolled given the first GSU's
    // delta
    static gfx::Vector2dF EstimateDisplacement(const gfx::Vector2dF& first_delta);
  
    // Returns the delta that should be scrolled at |time|.
    virtual gfx::Vector2dF GetScrollDelta(base::TimeTicks time);
  
    // Updates |current_displacement_|. This sync is necessary because the node
    // might be scrolled by other calls and the scrolls might be clamped.
    void UpdateCurrentOffset(const gfx::PointF& current_offset);
  
    // Returns true if the scroll has arrived at the snap destination.
    virtual bool IsFinished() const;
  
    base::TimeDelta duration() const { return duration_; }
  
   private:
    // Returns the curve's current distance at |current_time|.
    double GetCurrentCurveDistance(base::TimeDelta current_time);
  
    // The initial scroll offset of the scroller.
    const gfx::PointF start_offset_;
  
    // The total displacement to the snap position.
    const gfx::Vector2dF total_displacement_;
    // 1D representation of |total_displacement_|.
    const double total_distance_;
  
    // The current displacement that has been scrolled.
    gfx::Vector2dF current_displacement_;
  
    // The timestamp of the first GSU.
    const base::TimeTicks start_time_;
  
    // The number of deltas in the curve's geometric sequence.
    const double total_frames_;
    // The first delta that defines the curve's geometric sequence.
    const double first_delta_;
    // The total milliseconds needed to finish the curve.
    const base::TimeDelta duration_;
  
    bool is_finished_ = false;
  
    // |total_displacement_.x| / |total_distance_|
    double ratio_x_;
    // |total_displacement_.y| / |total_distance_|
    double ratio_y_;
  };
  
  }  // namespace cc
  
  #endif  // CC_INPUT_SNAP_FLING_CURVE_H_
  