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 MockRenderWidgetHost;
  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   // The result of |DispatchEvent()|, indicating either how the event was
  42   // handled, or how it should be handled by the caller.
  43   enum Disposition {
  44     CONSUMED,
  45     SHOULD_FORWARD_TO_RENDERER,
  46     SHOULD_FORWARD_TO_GESTURE_QUEUE
  47   };
  48   // This must be called when dispatching any event from the
  49   // RenderWidgetHostView so that the state of the overscroll gesture can be
  50   // updated properly.
  51   Disposition DispatchEvent(const blink::WebInputEvent& event,
  52                             const ui::LatencyInfo& latency_info);
  53
  54   // This must be called when the ACK for any event comes in. This updates the
  55   // overscroll gesture status as appropriate.
  56   void ReceivedEventACK(const blink::WebInputEvent& event, bool processed);
  57
  58   // This must be called when a gesture event is filtered out and not sent to
  59   // the renderer.
  60   void DiscardingGestureEvent(const blink::WebGestureEvent& event);
  61
  62   OverscrollMode overscroll_mode() const { return overscroll_mode_; }
  63
  64   void set_delegate(OverscrollControllerDelegate* delegate) {
  65     delegate_ = delegate;
  66   }
  67
  68   // Resets internal states.
  69   void Reset();
  70
  71   // Cancels any in-progress overscroll (and calls OnOverscrollModeChange on the
  72   // delegate if necessary), and resets internal states.
  73   void Cancel();
  74
  75  private:
  76   friend class MockRenderWidgetHost;
  77
  78   // Different scrolling states.
  79   enum ScrollState {
  80     STATE_UNKNOWN,
  81     STATE_PENDING,
  82     STATE_CONTENT_SCROLLING,
  83     STATE_OVERSCROLLING,
  84   };
  85
  86   // Returns true if the event indicates that the in-progress overscroll gesture
  87   // can now be completed.
  88   bool DispatchEventCompletesAction(
  89       const blink::WebInputEvent& event) const;
  90
  91   // Returns true to indicate that dispatching the event should reset the
  92   // overscroll gesture status.
  93   bool DispatchEventResetsState(const blink::WebInputEvent& event) const;
  94
  95   // Processes an event to update the internal state for overscroll. Returns
  96   // true if the state is updated, false otherwise.
  97   bool ProcessEventForOverscroll(const blink::WebInputEvent& event);
  98
  99   // Processes horizontal overscroll. This can update both the overscroll mode
 100   // and the over scroll amount (i.e. |overscroll_mode_|, |overscroll_delta_x_|
 101   // and |overscroll_delta_y_|).
 102   void ProcessOverscroll(float delta_x,
 103                          float delta_y,
 104                          blink::WebInputEvent::Type event_type);
 105
 106   // Completes the desired action from the current gesture.
 107   void CompleteAction();
 108
 109   // Sets the overscroll mode (and triggers callback in the delegate when
 110   // appropriate).
 111   void SetOverscrollMode(OverscrollMode new_mode);
 112
 113   // The current state of overscroll gesture.
 114   OverscrollMode overscroll_mode_;
 115
 116   // Used to keep track of the scrolling state.
 117   // If scrolling starts, and some scroll events are consumed at the beginning
 118   // of the scroll (i.e. some content on the web-page was scrolled), then do not
 119   // process any of the subsequent scroll events for generating overscroll
 120   // gestures.
 121   ScrollState scroll_state_;
 122
 123   // The amount of overscroll in progress. These values are invalid when
 124   // |overscroll_mode_| is set to OVERSCROLL_NONE.
 125   float overscroll_delta_x_;
 126   float overscroll_delta_y_;
 127
 128   // The delegate that receives the overscroll updates. The delegate is not
 129   // owned by this controller.
 130   OverscrollControllerDelegate* delegate_;
 131
 132   DISALLOW_COPY_AND_ASSIGN(OverscrollController);
 133 };
 134
 135 }  // namespace content
 136
 137 #endif  // CONTENT_BROWSER_RENDERER_HOST_OVERSCROLL_CONTROLLER_H_