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