content/renderer/accessibility/renderer_accessibility.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_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_
   6 #define CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_
   7
   8 #include <vector>
   9
  10 #include "base/containers/hash_tables.h"
  11 #include "base/memory/weak_ptr.h"
  12 #include "content/common/accessibility_messages.h"
  13 #include "content/public/renderer/render_frame_observer.h"
  14 #include "content/renderer/accessibility/blink_ax_tree_source.h"
  15 #include "third_party/WebKit/public/web/WebAXObject.h"
  16 #include "ui/accessibility/ax_tree_serializer.h"
  17
  18 namespace blink {
  19 class WebDocument;
  20 class WebNode;
  21 };
  22
  23 namespace content {
  24 class RenderFrameImpl;
  25
  26 // The browser process implements native accessibility APIs, allowing
  27 // assistive technology (e.g., screen readers, magnifiers) to access and
  28 // control the web contents with high-level APIs. These APIs are also used
  29 // by automation tools, and Windows 8 uses them to determine when the
  30 // on-screen keyboard should be shown.
  31 //
  32 // An instance of this class belongs to RenderFrameImpl. Accessibility is
  33 // initialized based on the AccessibilityMode of RenderFrameImpl; it lazily
  34 // starts as Off or EditableTextOnly depending on the operating system, and
  35 // switches to Complete if assistive technology is detected or a flag is set.
  36 //
  37 // A tree of accessible objects is built here and sent to the browser process;
  38 // the browser process maintains this as a tree of platform-native
  39 // accessible objects that can be used to respond to accessibility requests
  40 // from other processes.
  41 //
  42 // This class implements complete accessibility support for assistive
  43 // technology. It turns on Blink's accessibility code and sends a serialized
  44 // representation of that tree whenever it changes. It also handles requests
  45 // from the browser to perform accessibility actions on nodes in the tree
  46 // (e.g., change focus, or click on a button).
  47 class CONTENT_EXPORT RendererAccessibility : public RenderFrameObserver {
  48  public:
  49   explicit RendererAccessibility(RenderFrameImpl* render_frame);
  50   ~RendererAccessibility() override;
  51
  52   // RenderFrameObserver implementation.
  53   bool OnMessageReceived(const IPC::Message& message) override;
  54
  55   // Called when an accessibility notification occurs in Blink.
  56   void HandleWebAccessibilityEvent(const blink::WebAXObject& obj,
  57                                    blink::WebAXEvent event);
  58
  59   // Called when a new find in page result is highlighted.
  60   void HandleAccessibilityFindInPageResult(
  61       int identifier,
  62       int match_index,
  63       const blink::WebAXObject& start_object,
  64       int start_offset,
  65       const blink::WebAXObject& end_object,
  66       int end_offset);
  67
  68   void AccessibilityFocusedNodeChanged(const blink::WebNode& node);
  69
  70   // This can be called before deleting a RendererAccessibility instance due
  71   // to the accessibility mode changing, as opposed to during frame destruction
  72   // (when there'd be no point).
  73   void DisableAccessibility();
  74
  75   void HandleAXEvent(const blink::WebAXObject& obj, ui::AXEvent event);
  76
  77  protected:
  78   // Returns the main top-level document for this page, or NULL if there's
  79   // no view or frame.
  80   blink::WebDocument GetMainDocument();
  81
  82   // Send queued events from the renderer to the browser.
  83   void SendPendingAccessibilityEvents();
  84
  85   // Check the entire accessibility tree to see if any nodes have
  86   // changed location, by comparing their locations to the cached
  87   // versions. If any have moved, send an IPC with the new locations.
  88   void SendLocationChanges();
  89
  90   // The RenderFrameImpl that owns us.
  91   RenderFrameImpl* render_frame_;
  92
  93  private:
  94   // Handlers for messages from the browser to the renderer.
  95   void OnDoDefaultAction(int acc_obj_id);
  96   void OnEventsAck();
  97   void OnFatalError();
  98   void OnHitTest(gfx::Point point);
  99   void OnSetAccessibilityFocus(int acc_obj_id);
 100   void OnReset(int reset_token);
 101   void OnScrollToMakeVisible(int acc_obj_id, gfx::Rect subfocus);
 102   void OnScrollToPoint(int acc_obj_id, gfx::Point point);
 103   void OnSetFocus(int acc_obj_id);
 104   void OnSetTextSelection(int acc_obj_id, int start_offset, int end_offset);
 105   void OnSetValue(int acc_obj_id, base::string16 value);
 106
 107   // Events from Blink are collected until they are ready to be
 108   // sent to the browser.
 109   std::vector<AccessibilityHostMsg_EventParams> pending_events_;
 110
 111   // The adapter that exposes Blink's accessibility tree to AXTreeSerializer.
 112   BlinkAXTreeSource tree_source_;
 113
 114   // The serializer that sends accessibility messages to the browser process.
 115   ui::AXTreeSerializer<blink::WebAXObject> serializer_;
 116
 117   // Current location of every object, so we can detect when it moves.
 118   base::hash_map<int, gfx::Rect> locations_;
 119
 120   // The most recently observed scroll offset of the root document element.
 121   // TODO(dmazzoni): remove once https://bugs.webkit.org/show_bug.cgi?id=73460
 122   // is fixed.
 123   gfx::Size last_scroll_offset_;
 124
 125   // Set if we are waiting for an accessibility event ack.
 126   bool ack_pending_;
 127
 128   // Nonzero if the browser requested we reset the accessibility state.
 129   // We need to return this token in the next IPC.
 130   int reset_token_;
 131
 132   // So we can queue up tasks to be executed later.
 133   base::WeakPtrFactory<RendererAccessibility> weak_factory_;
 134
 135   DISALLOW_COPY_AND_ASSIGN(RendererAccessibility);
 136 };
 137
 138 }  // namespace content
 139
 140 #endif  // CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_