layout/generic/ScrollbarActivity.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef ScrollbarActivity_h___
   8 #define ScrollbarActivity_h___
   9
  10 #include "mozilla/Assertions.h"
  11 #include "nsCOMPtr.h"
  12 #include "nsIDOMEventListener.h"
  13
  14 class nsIContent;
  15 class nsIScrollbarMediator;
  16 class nsITimer;
  17
  18 namespace mozilla {
  19
  20 namespace dom {
  21 class Element;
  22 class EventTarget;
  23 }  // namespace dom
  24
  25 namespace layout {
  26
  27 /**
  28  * ScrollbarActivity
  29  *
  30  * This class manages scrollbar behavior that imitates the native Mac OS X
  31  * Lion overlay scrollbar behavior: Scrollbars are only shown while "scrollbar
  32  * activity" occurs, and they're hidden with a fade animation after a short
  33  * delay.
  34  *
  35  * Scrollbar activity has these states:
  36  *  - inactive:
  37  *      Scrollbars are hidden.
  38  *  - ongoing activity:
  39  *      Scrollbars are visible and being operated on in some way, for example
  40  *      because they're hovered or pressed.
  41  *  - active, but waiting for fade out
  42  *      Scrollbars are still completely visible but are about to fade away.
  43  *  - fading out
  44  *      Scrollbars are subject to a fade-out animation.
  45  *
  46  * Initial scrollbar activity needs to be reported by the scrollbar holder that
  47  * owns the ScrollbarActivity instance. This needs to happen via a call to
  48  * ActivityOccurred(), for example when the current scroll position or the size
  49  * of the scroll area changes.
  50  *
  51  * As soon as scrollbars are visible, the ScrollbarActivity class manages the
  52  * rest of the activity behavior: It ensures that mouse motions inside the
  53  * scroll area keep the scrollbars visible, and that scrollbars don't fade away
  54  * while they're being hovered / dragged. It also sets a sticky hover attribute
  55  * on the most recently hovered scrollbar.
  56  *
  57  * ScrollbarActivity falls into hibernation after the scrollbars have faded
  58  * out. It only starts acting after the next call to ActivityOccurred() /
  59  * ActivityStarted().
  60  */
  61
  62 class ScrollbarActivity final : public nsIDOMEventListener {
  63  public:
  64   explicit ScrollbarActivity(nsIScrollbarMediator* aScrollableFrame)
  65       : mScrollableFrame(aScrollableFrame) {
  66     MOZ_ASSERT(mScrollableFrame);
  67   }
  68
  69   NS_DECL_ISUPPORTS
  70   NS_DECL_NSIDOMEVENTLISTENER
  71
  72   void Destroy();
  73
  74   void ActivityOccurred();
  75   void ActivityStarted();
  76   void ActivityStopped();
  77
  78   bool IsActive() const { return mNestedActivityCounter; }
  79
  80  protected:
  81   virtual ~ScrollbarActivity() = default;
  82
  83   void StartFadeTimer();
  84   void CancelFadeTimer();
  85   void BeginFade();
  86   void HandleEventForScrollbar(const nsAString& aType, nsIContent* aTarget,
  87                                dom::Element* aScrollbar,
  88                                bool* aStoredHoverState);
  89
  90   void StartListeningForScrollbarEvents();
  91   void StartListeningForScrollAreaEvents();
  92   void StopListeningForScrollbarEvents();
  93   void StopListeningForScrollAreaEvents();
  94   void AddScrollbarEventListeners(dom::EventTarget* aScrollbar);
  95   void RemoveScrollbarEventListeners(dom::EventTarget* aScrollbar);
  96
  97   void HoveredScrollbar(dom::Element* aScrollbar);
  98
  99   dom::Element* GetScrollbarContent(bool aVertical);
 100   dom::Element* GetHorizontalScrollbar() { return GetScrollbarContent(false); }
 101   dom::Element* GetVerticalScrollbar() { return GetScrollbarContent(true); }
 102
 103   nsIScrollbarMediator* const mScrollableFrame;
 104   nsCOMPtr<dom::EventTarget> mHorizontalScrollbar;  // null while inactive
 105   nsCOMPtr<dom::EventTarget> mVerticalScrollbar;    // null while inactive
 106   nsCOMPtr<nsITimer> mFadeTimer;
 107   uint32_t mNestedActivityCounter = 0;
 108   // This boolean is true from the point activity starts to the point BeginFade
 109   // runs, and effectively reflects the "active" attribute of the scrollbar.
 110   bool mScrollbarEffectivelyVisible = false;
 111   bool mListeningForScrollbarEvents = false;
 112   bool mListeningForScrollAreaEvents = false;
 113   bool mHScrollbarHovered = false;
 114   bool mVScrollbarHovered = false;
 115 };
 116
 117 }  // namespace layout
 118 }  // namespace mozilla
 119
 120 #endif /* ScrollbarActivity_h___ */