content/browser/renderer_host/overscroll_controller.h

   1 // Copyright (c) 2012 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 CONTENT_BROWSER_RENDERER_HOST_OVERSCROLL_CONTROLLER_H_
   6 #define CONTENT_BROWSER_RENDERER_HOST_OVERSCROLL_CONTROLLER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/compiler_specific.h"
  10 #include "third_party/WebKit/public/web/WebInputEvent.h"
  11
  12 namespace ui {
  13 class LatencyInfo;
  14 }
  15
  16 namespace content {
  17
  18 class RenderWidgetHostViewAuraOverscrollTest;
  19 class OverscrollControllerDelegate;
  20
  21 // Indicates the direction that the scroll is heading in relative to the screen,
  22 // with the top being NORTH.
  23 enum OverscrollMode {
  24   OVERSCROLL_NONE,
  25   OVERSCROLL_NORTH,
  26   OVERSCROLL_SOUTH,
  27   OVERSCROLL_WEST,
  28   OVERSCROLL_EAST
  29 };
  30
  31 // When a page is scrolled beyond the scrollable region, it will trigger an
  32 // overscroll gesture. This controller receives the events that are dispatched
  33 // to the renderer, and the ACKs of events, and updates the overscroll gesture
  34 // status accordingly.
  35 class OverscrollController {
  36  public:
  37   OverscrollController();
  38   virtual ~OverscrollController();
  39
  40   // This must be called when dispatching any event from the
  41   // RenderWidgetHostView so that the state of the overscroll gesture can be
  42   // updated properly. Returns true if the event was handled, in which case
  43   // further processing should cease.
  44   bool WillHandleEvent(const blink::WebInputEvent& event);
  45
  46   // This must be called when the ACK for any event comes in. This updates the
  47   // overscroll gesture status as appropriate.
  48   void ReceivedEventACK(const blink::WebInputEvent& event, bool processed);
  49
  50   // This must be called when a gesture event is filtered out and not sent to
  51   // the renderer.
  52   void DiscardingGestureEvent(const blink::WebGestureEvent& event);
  53
  54   OverscrollMode overscroll_mode() const { return overscroll_mode_; }
  55
  56   void set_delegate(OverscrollControllerDelegate* delegate) {
  57     delegate_ = delegate;
  58   }
  59
  60   // Resets internal states.
  61   void Reset();
  62
  63   // Cancels any in-progress overscroll (and calls OnOverscrollModeChange on the
  64   // delegate if necessary), and resets internal states.
  65   void Cancel();
  66
  67  private:
  68   friend class RenderWidgetHostViewAuraOverscrollTest;
  69
  70   // Different scrolling states.
  71   enum ScrollState {
  72     STATE_UNKNOWN,
  73     STATE_PENDING,
  74     STATE_CONTENT_SCROLLING,
  75     STATE_OVERSCROLLING,
  76   };
  77
  78   // Returns true if the event indicates that the in-progress overscroll gesture
  79   // can now be completed.
  80   bool DispatchEventCompletesAction(
  81       const blink::WebInputEvent& event) const;
  82
  83   // Returns true to indicate that dispatching the event should reset the
  84   // overscroll gesture status.
  85   bool DispatchEventResetsState(const blink::WebInputEvent& event) const;
  86
  87   // Processes an event to update the internal state for overscroll. Returns
  88   // true if the state is updated, false otherwise.
  89   bool ProcessEventForOverscroll(const blink::WebInputEvent& event);
  90
  91   // Processes horizontal overscroll. This can update both the overscroll mode
  92   // and the over scroll amount (i.e. |overscroll_mode_|, |overscroll_delta_x_|
  93   // and |overscroll_delta_y_|). Returns true if overscroll was handled by the
  94   // delegate.
  95   bool ProcessOverscroll(float delta_x,
  96                          float delta_y,
  97                          blink::WebInputEvent::Type event_type);
  98
  99   // Completes the desired action from the current gesture.
 100   void CompleteAction();
 101
 102   // Sets the overscroll mode (and triggers callback in the delegate when
 103   // appropriate).
 104   void SetOverscrollMode(OverscrollMode new_mode);
 105
 106   // The current state of overscroll gesture.
 107   OverscrollMode overscroll_mode_;
 108
 109   // Used to keep track of the scrolling state.
 110   // If scrolling starts, and some scroll events are consumed at the beginning
 111   // of the scroll (i.e. some content on the web-page was scrolled), then do not
 112   // process any of the subsequent scroll events for generating overscroll
 113   // gestures.
 114   ScrollState scroll_state_;
 115
 116   // The amount of overscroll in progress. These values are invalid when
 117   // |overscroll_mode_| is set to OVERSCROLL_NONE.
 118   float overscroll_delta_x_;
 119   float overscroll_delta_y_;
 120
 121   // The delegate that receives the overscroll updates. The delegate is not
 122   // owned by this controller.
 123   OverscrollControllerDelegate* delegate_;
 124
 125   DISALLOW_COPY_AND_ASSIGN(OverscrollController);
 126 };
 127
 128 }  // namespace content
 129
 130 #endif  // CONTENT_BROWSER_RENDERER_HOST_OVERSCROLL_CONTROLLER_H_