content/browser/accessibility/browser_accessibility_state_impl.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_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
   6 #define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
   7
   8 #include <vector>
   9
  10 #include "base/basictypes.h"
  11 #include "base/compiler_specific.h"
  12 #include "base/memory/singleton.h"
  13 #include "content/common/accessibility_mode_enums.h"
  14 #include "content/public/browser/browser_accessibility_state.h"
  15
  16 namespace content {
  17
  18 // The BrowserAccessibilityState class is used to determine if Chrome should be
  19 // customized for users with assistive technology, such as screen readers. We
  20 // modify the behavior of certain user interfaces to provide a better experience
  21 // for screen reader users. The way we detect a screen reader program is
  22 // different for each platform.
  23 //
  24 // Screen Reader Detection
  25 // (1) On windows many screen reader detection mechinisms will give false
  26 // positives like relying on the SPI_GETSCREENREADER system parameter. In Chrome
  27 // we attempt to dynamically detect a MSAA client screen reader by calling
  28 // NotifiyWinEvent in NativeWidgetWin with a custom ID and wait to see if the ID
  29 // is requested by a subsequent call to WM_GETOBJECT.
  30 // (2) On mac we detect dynamically if VoiceOver is running.  We rely upon the
  31 // undocumented accessibility attribute @"AXEnhancedUserInterface" which is set
  32 // when VoiceOver is launched and unset when VoiceOver is closed.  This is an
  33 // improvement over reading defaults preference values (which has no callback
  34 // mechanism).
  35 class CONTENT_EXPORT BrowserAccessibilityStateImpl
  36     : public base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>,
  37       public BrowserAccessibilityState {
  38  public:
  39   BrowserAccessibilityStateImpl();
  40
  41   static BrowserAccessibilityStateImpl* GetInstance();
  42
  43   void EnableAccessibility() override;
  44   void DisableAccessibility() override;
  45   void ResetAccessibilityMode() override;
  46   void OnScreenReaderDetected() override;
  47   bool IsAccessibleBrowser() override;
  48   void AddHistogramCallback(base::Closure callback) override;
  49
  50   void UpdateHistogramsForTesting() override;
  51
  52   AccessibilityMode accessibility_mode() const { return accessibility_mode_; };
  53
  54   // Adds the given accessibility mode to the current accessibility mode bitmap.
  55   void AddAccessibilityMode(AccessibilityMode mode);
  56
  57   // Removes the given accessibility mode from the current accessibility mode
  58   // bitmap, managing the bits that are shared with other modes such that a
  59   // bit will only be turned off when all modes that depend on it have been
  60   // removed.
  61   void RemoveAccessibilityMode(AccessibilityMode mode);
  62
  63  private:
  64   friend class base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>;
  65   friend struct DefaultSingletonTraits<BrowserAccessibilityStateImpl>;
  66
  67   // Resets accessibility_mode_ to the default value.
  68   void ResetAccessibilityModeValue();
  69
  70   // Called a short while after startup to allow time for the accessibility
  71   // state to be determined. Updates histograms with the current state.
  72   void UpdateHistograms();
  73
  74   // Leaky singleton, destructor generally won't be called.
  75   ~BrowserAccessibilityStateImpl() override;
  76
  77   void UpdatePlatformSpecificHistograms();
  78
  79   // Updates the accessibility mode of all web contents, including swapped out
  80   // ones. |add| specifies whether the mode should be added or removed.
  81   void AddOrRemoveFromAllWebContents(AccessibilityMode mode, bool add);
  82
  83   AccessibilityMode accessibility_mode_;
  84
  85   std::vector<base::Closure> histogram_callbacks_;
  86
  87   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityStateImpl);
  88 };
  89
  90 }  // namespace content
  91
  92 #endif  // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_