ui/events/gestures/fling_curve.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_EVENTS_GESTURES_FLING_CURVE_H_
   6 #define UI_EVENTS_GESTURES_FLING_CURVE_H_
   7
   8 #include "base/time/time.h"
   9 #include "ui/events/events_base_export.h"
  10 #include "ui/events/gesture_curve.h"
  11 #include "ui/gfx/geometry/point_f.h"
  12 #include "ui/gfx/geometry/vector2d_f.h"
  13
  14 namespace ui {
  15
  16 // FlingCurve can be used to scroll a UI element suitable for touch screen-based
  17 // flings.
  18 class EVENTS_BASE_EXPORT FlingCurve : public GestureCurve {
  19  public:
  20   FlingCurve(const gfx::Vector2dF& velocity, base::TimeTicks start_timestamp);
  21   ~FlingCurve() override;
  22
  23   // GestureCurve implementation.
  24   bool ComputeScrollOffset(base::TimeTicks time,
  25                            gfx::Vector2dF* offset,
  26                            gfx::Vector2dF* velocity) override;
  27
  28   // In contrast to |ComputeScrollOffset()|, this method is stateful and
  29   // returns the *change* in scroll offset between successive calls.
  30   // Returns true as long as the curve is still active and requires additional
  31   // animation ticks.
  32   bool ComputeScrollDeltaAtTime(base::TimeTicks current, gfx::Vector2dF* delta);
  33
  34  private:
  35   const float curve_duration_;
  36   const base::TimeTicks start_timestamp_;
  37
  38   gfx::Vector2dF displacement_ratio_;
  39   gfx::Vector2dF cumulative_scroll_;
  40   base::TimeTicks previous_timestamp_;
  41   float time_offset_;
  42   float position_offset_;
  43
  44   DISALLOW_COPY_AND_ASSIGN(FlingCurve);
  45 };
  46
  47 }  // namespace ui
  48
  49 #endif  // UI_EVENTS_GESTURES_FLING_CURVE_H_