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      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 MockRenderWidgetHost;
     19 class OverscrollControllerDelegate;
     20 class RenderWidgetHostImpl;
     21 
     22 // Indicates the direction that the scroll is heading in relative to the screen,
     23 // with the top being NORTH.
     24 enum OverscrollMode {
     25   OVERSCROLL_NONE,
     26   OVERSCROLL_NORTH,
     27   OVERSCROLL_SOUTH,
     28   OVERSCROLL_WEST,
     29   OVERSCROLL_EAST,
     30   OVERSCROLL_COUNT
     31 };
     32 
     33 // When a page is scrolled beyond the scrollable region, it will trigger an
     34 // overscroll gesture. This controller receives the events that are dispatched
     35 // to the renderer, and the ACKs of events, and updates the overscroll gesture
     36 // status accordingly.
     37 class OverscrollController {
     38  public:
     39   // Creates an overscroll controller for the specified RenderWidgetHost.
     40   // The RenderWidgetHost owns this overscroll controller.
     41   explicit OverscrollController(RenderWidgetHostImpl* widget_host);
     42   virtual ~OverscrollController();
     43 
     44   // This must be called when dispatching any event from the
     45   // RenderWidgetHostView so that the state of the overscroll gesture can be
     46   // updated properly.
     47   // Returns true if the event should be dispatched, false otherwise.
     48   bool WillDispatchEvent(const WebKit::WebInputEvent& event,
     49                          const ui::LatencyInfo& latency_info);
     50 
     51   // This must be called when the ACK for any event comes in. This updates the
     52   // overscroll gesture status as appropriate.
     53   void ReceivedEventACK(const WebKit::WebInputEvent& event, bool processed);
     54 
     55   // This must be called when a gesture event is filtered out and not sent to
     56   // the renderer.
     57   void DiscardingGestureEvent(const WebKit::WebGestureEvent& event);
     58 
     59   OverscrollMode overscroll_mode() const { return overscroll_mode_; }
     60 
     61   void set_delegate(OverscrollControllerDelegate* delegate) {
     62     delegate_ = delegate;
     63   }
     64 
     65   // Resets internal states.
     66   void Reset();
     67 
     68   // Cancels any in-progress overscroll (and calls OnOverscrollModeChange on the
     69   // delegate if necessary), and resets internal states.
     70   void Cancel();
     71 
     72  private:
     73   friend class MockRenderWidgetHost;
     74 
     75   // Different scrolling states.
     76   enum ScrollState {
     77     STATE_UNKNOWN,
     78     STATE_PENDING,
     79     STATE_CONTENT_SCROLLING,
     80     STATE_OVERSCROLLING,
     81   };
     82 
     83   // Returns true if the event indicates that the in-progress overscroll gesture
     84   // can now be completed.
     85   bool DispatchEventCompletesAction(
     86       const WebKit::WebInputEvent& event) const;
     87 
     88   // Returns true to indicate that dispatching the event should reset the
     89   // overscroll gesture status.
     90   bool DispatchEventResetsState(const WebKit::WebInputEvent& event) const;
     91 
     92   // Processes an event and updates internal state for overscroll.
     93   void ProcessEventForOverscroll(const WebKit::WebInputEvent& event);
     94 
     95   // Processes horizontal overscroll. This can update both the overscroll mode
     96   // and the over scroll amount (i.e. |overscroll_mode_|, |overscroll_delta_x_|
     97   // and |overscroll_delta_y_|).
     98   void ProcessOverscroll(float delta_x, float delta_y);
     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   // Returns whether the input event should be forwarded to the
    108   // RenderWidgetHost.
    109   bool ShouldForwardToHost(const WebKit::WebInputEvent& event) const;
    110 
    111   // The RenderWidgetHost that owns this overscroll controller.
    112   RenderWidgetHostImpl* render_widget_host_;
    113 
    114   // The current state of overscroll gesture.
    115   OverscrollMode overscroll_mode_;
    116 
    117   // Used to keep track of the scrolling state.
    118   // If scrolling starts, and some scroll events are consumed at the beginning
    119   // of the scroll (i.e. some content on the web-page was scrolled), then do not
    120   // process any of the subsequent scroll events for generating overscroll
    121   // gestures.
    122   ScrollState scroll_state_;
    123 
    124   // The amount of overscroll in progress. These values are invalid when
    125   // |overscroll_mode_| is set to OVERSCROLL_NONE.
    126   float overscroll_delta_x_;
    127   float overscroll_delta_y_;
    128 
    129   // The delegate that receives the overscroll updates. The delegate is not
    130   // owned by this controller.
    131   OverscrollControllerDelegate* delegate_;
    132 
    133   DISALLOW_COPY_AND_ASSIGN(OverscrollController);
    134 };
    135 
    136 }  // namespace content
    137 
    138 #endif  // CONTENT_BROWSER_RENDERER_HOST_OVERSCROLL_CONTROLLER_H_
    139