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   // Request a one-time snapshot of the accessibility tree without
  50   // enabling accessibility if it wasn't already enabled.
  51   static void SnapshotAccessibilityTree(RenderFrameImpl* render_frame,
  52                                         ui::AXTreeUpdate* response);
  53
  54   explicit RendererAccessibility(RenderFrameImpl* render_frame);
  55   ~RendererAccessibility() override;
  56
  57   // RenderFrameObserver implementation.
  58   bool OnMessageReceived(const IPC::Message& message) override;
  59
  60   // Called when an accessibility notification occurs in Blink.
  61   void HandleWebAccessibilityEvent(const blink::WebAXObject& obj,
  62                                    blink::WebAXEvent event);
  63
  64   // Called when a new find in page result is highlighted.
  65   void HandleAccessibilityFindInPageResult(
  66       int identifier,
  67       int match_index,
  68       const blink::WebAXObject& start_object,
  69       int start_offset,
  70       const blink::WebAXObject& end_object,
  71       int end_offset);
  72
  73   void AccessibilityFocusedNodeChanged(const blink::WebNode& node);
  74
  75   // This can be called before deleting a RendererAccessibility instance due
  76   // to the accessibility mode changing, as opposed to during frame destruction
  77   // (when there'd be no point).
  78   void DisableAccessibility();
  79
  80   void HandleAXEvent(const blink::WebAXObject& obj, ui::AXEvent event);
  81
  82  protected:
  83   // Returns the main top-level document for this page, or NULL if there's
  84   // no view or frame.
  85   blink::WebDocument GetMainDocument();
  86
  87   // Send queued events from the renderer to the browser.
  88   void SendPendingAccessibilityEvents();
  89
  90   // Check the entire accessibility tree to see if any nodes have
  91   // changed location, by comparing their locations to the cached
  92   // versions. If any have moved, send an IPC with the new locations.
  93   void SendLocationChanges();
  94
  95   // The RenderFrameImpl that owns us.
  96   RenderFrameImpl* render_frame_;
  97
  98  private:
  99   // Handlers for messages from the browser to the renderer.
 100   void OnDoDefaultAction(int acc_obj_id);
 101   void OnEventsAck();
 102   void OnFatalError();
 103   void OnHitTest(gfx::Point point);
 104   void OnSetAccessibilityFocus(int acc_obj_id);
 105   void OnReset(int reset_token);
 106   void OnScrollToMakeVisible(int acc_obj_id, gfx::Rect subfocus);
 107   void OnScrollToPoint(int acc_obj_id, gfx::Point point);
 108   void OnSetScrollOffset(int acc_obj_id, gfx::Point offset);
 109   void OnSetFocus(int acc_obj_id);
 110   void OnSetTextSelection(int acc_obj_id, int start_offset, int end_offset);
 111   void OnSetValue(int acc_obj_id, base::string16 value);
 112   void OnShowContextMenu(int acc_obj_id);
 113
 114   // Events from Blink are collected until they are ready to be
 115   // sent to the browser.
 116   std::vector<AccessibilityHostMsg_EventParams> pending_events_;
 117
 118   // The adapter that exposes Blink's accessibility tree to AXTreeSerializer.
 119   BlinkAXTreeSource tree_source_;
 120
 121   // The serializer that sends accessibility messages to the browser process.
 122   ui::AXTreeSerializer<blink::WebAXObject> serializer_;
 123
 124   // Current location of every object, so we can detect when it moves.
 125   base::hash_map<int, gfx::Rect> locations_;
 126
 127   // The most recently observed scroll offset of the root document element.
 128   // TODO(dmazzoni): remove once https://bugs.webkit.org/show_bug.cgi?id=73460
 129   // is fixed.
 130   gfx::Size last_scroll_offset_;
 131
 132   // Set if we are waiting for an accessibility event ack.
 133   bool ack_pending_;
 134
 135   // Nonzero if the browser requested we reset the accessibility state.
 136   // We need to return this token in the next IPC.
 137   int reset_token_;
 138
 139   // So we can queue up tasks to be executed later.
 140   base::WeakPtrFactory<RendererAccessibility> weak_factory_;
 141
 142   DISALLOW_COPY_AND_ASSIGN(RendererAccessibility);
 143 };
 144
 145 }  // namespace content
 146
 147 #endif  // CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_H_