ui/events/gesture_detection/snap_scroll_controller.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_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
   6 #define UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "ui/events/gesture_detection/gesture_detection_export.h"
  10
  11 namespace ui {
  12
  13 class MotionEvent;
  14 class ZoomManager;
  15
  16 // Port of SnapScrollController.java from Chromium
  17 // Controls the scroll snapping behavior based on scroll updates.
  18 class SnapScrollController {
  19  public:
  20   struct GESTURE_DETECTION_EXPORT Config {
  21     Config();
  22     ~Config();
  23     int screen_width_pixels;
  24     int screen_height_pixels;
  25     float device_scale_factor;
  26   };
  27
  28   explicit SnapScrollController(const Config& config);
  29   ~SnapScrollController();
  30
  31   // Updates the snap scroll mode based on the given X and Y distance to be
  32   // moved on scroll.  If the scroll update is above a threshold, the snapping
  33   // behavior is reset.
  34   void UpdateSnapScrollMode(float distance_x, float distance_y);
  35
  36   // Sets the snap scroll mode based on the event type.
  37   void SetSnapScrollingMode(const MotionEvent& event,
  38                             bool is_scale_gesture_detection_in_progress);
  39
  40   void ResetSnapScrollMode() { snap_scroll_mode_ = SNAP_NONE; }
  41   bool IsSnapVertical() const { return snap_scroll_mode_ == SNAP_VERT; }
  42   bool IsSnapHorizontal() const { return snap_scroll_mode_ == SNAP_HORIZ; }
  43   bool IsSnappingScrolls() const { return snap_scroll_mode_ != SNAP_NONE; }
  44
  45  private:
  46   enum SnapMode {
  47     SNAP_NONE,
  48     SNAP_HORIZ,
  49     SNAP_VERT
  50   };
  51
  52   static float CalculateChannelDistance(const Config& config);
  53
  54   float channel_distance_;
  55   SnapMode snap_scroll_mode_;
  56   float first_touch_x_;
  57   float first_touch_y_;
  58   float distance_x_;
  59   float distance_y_;
  60
  61   DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
  62 };
  63
  64 }  // namespace ui
  65
  66 #endif  // UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_