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The Tor Browser
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ScrollbarActivity.h (3468B)

      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 
     87  void StartListeningForScrollAreaEvents();
     88  void StopListeningForScrollAreaEvents();
     89 
     90  dom::Element* GetScrollbarContent(bool aVertical);
     91  dom::Element* GetHorizontalScrollbar() { return GetScrollbarContent(false); }
     92  dom::Element* GetVerticalScrollbar() { return GetScrollbarContent(true); }
     93 
     94  nsIScrollbarMediator* const mScrollableFrame;
     95  nsCOMPtr<nsITimer> mFadeTimer;
     96  uint32_t mNestedActivityCounter = 0;
     97  // This boolean is true from the point activity starts to the point BeginFade
     98  // runs, and effectively reflects the "active" attribute of the scrollbar.
     99  bool mScrollbarEffectivelyVisible = false;
    100  bool mListeningForScrollAreaEvents = false;
    101 };
    102 
    103 }  // namespace layout
    104 }  // namespace mozilla
    105 
    106 #endif /* ScrollbarActivity_h___ */