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
16namespace 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).
35class CONTENT_EXPORT BrowserAccessibilityStateImpl
36    : public base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>,
37      public BrowserAccessibilityState {
38 public:
39  BrowserAccessibilityStateImpl();
40
41  static BrowserAccessibilityStateImpl* GetInstance();
42
43  virtual void EnableAccessibility() OVERRIDE;
44  virtual void DisableAccessibility() OVERRIDE;
45  virtual void ResetAccessibilityMode() OVERRIDE;
46  virtual void OnScreenReaderDetected() OVERRIDE;
47  virtual bool IsAccessibleBrowser() OVERRIDE;
48  virtual void AddHistogramCallback(base::Closure callback) OVERRIDE;
49
50  virtual 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  virtual ~BrowserAccessibilityStateImpl();
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_
93