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Reimplement accessibility of web content by caching the entire
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accessibility tree in the browser process.

Adds new RPCs for a browser tab to request accessibility info from
a renderer; the renderer responds with a complete tree of
accessibility metadata for the entire DOM, which is then cached
in the RenderWidgetHostView. This part is cross-platform and will
help with accessibility on both Windows and Mac OS X.

For Windows, MSAA support for web content has been rewritten to
use this new cache. Tested in JAWS and NVDA screen readers.
Using Chrome with a screen reader is now fast and stable,
unlike the previous implementation. However, note that most
advanced functionality is still not supported, and much work remains
to make Chrome work well with a screen reader. This is a necessary
step to improve stability first.

BUG=25564
BUG=13291
TEST=See http://codereview.chromium.org/1806001

Review URL: http://codereview.chromium.org/1637018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@46842 0039d316-1c4b-4281-b951-d872f2087c98
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dmazzoni@chromium.org committed May 10, 2010
1 parent 611b66a commit fae40a3
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Showing 26 changed files with 5,506 additions and 1,173 deletions.
659 changes: 343 additions & 316 deletions chrome/browser/browser_accessibility.cc
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249 changes: 174 additions & 75 deletions chrome/browser/browser_accessibility.h
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

Expand All @@ -7,9 +7,13 @@

#include <atlbase.h>
#include <atlcom.h>

#include <oleacc.h>

#include <vector>

#include "base/scoped_comptr_win.h"
#include "chrome/browser/browser_accessibility_manager.h"
#include "ia2_api_all.h" // Generated
#include "webkit/glue/webaccessibility.h"

using webkit_glue::WebAccessibility;
Expand All @@ -25,29 +29,58 @@ using webkit_glue::WebAccessibility;
////////////////////////////////////////////////////////////////////////////////
class ATL_NO_VTABLE BrowserAccessibility
: public CComObjectRootEx<CComMultiThreadModel>,
public IDispatchImpl<IAccessible, &IID_IAccessible, &LIBID_Accessibility> {
public IDispatchImpl<IAccessible2, &IID_IAccessible2,
&LIBID_IAccessible2Lib>,
public IServiceProvider {
public:
BEGIN_COM_MAP(BrowserAccessibility)
COM_INTERFACE_ENTRY2(IDispatch, IAccessible)
COM_INTERFACE_ENTRY(IAccessible)
COM_INTERFACE_ENTRY2(IDispatch, IAccessible2)
COM_INTERFACE_ENTRY2(IAccessible, IAccessible2)
COM_INTERFACE_ENTRY(IAccessible2)
COM_INTERFACE_ENTRY(IServiceProvider)
END_COM_MAP()

BrowserAccessibility()
: iaccessible_id_(-1),
routing_id_(-1),
process_id_(-1),
parent_hwnd_(NULL),
instance_active_(false) {
}
BrowserAccessibility();

virtual ~BrowserAccessibility();

// Initialize this object and mark it as active.
void Initialize(BrowserAccessibilityManager* manager,
BrowserAccessibility* parent,
LONG child_id,
LONG index_in_parent,
const webkit_glue::WebAccessibility& src);

// Add a child of this object.
void AddChild(BrowserAccessibility* child);

// Mark this object as inactive, and remove references to all children.
// When no other clients hold any references to this object it will be
// deleted, and in the meantime, calls to any methods will return E_FAIL.
void InactivateTree();

// Return true if this object is equal to or a descendant of |ancestor|.
bool IsDescendantOf(BrowserAccessibility* ancestor);

// Return the previous sibling of this object, or NULL if it's the first
// child of its parent.
BrowserAccessibility* GetPreviousSibling();

// Return the next sibling of this object, or NULL if it's the last child
// of its parent.
BrowserAccessibility* GetNextSibling();

~BrowserAccessibility() {}
// Accessors
LONG child_id() { return child_id_; }

HRESULT Initialize(int iaccessible_id,
int routing_id,
int process_id,
HWND parent_hwnd);
// Add one to the reference count and return the same object. Always
// use this method when returning a BrowserAccessibility object as
// an output parameter to a COM interface, never use it otherwise.
BrowserAccessibility* NewReference();

// Supported IAccessible methods.
//
// IAccessible methods.
//

// Performs the default action on a given object.
STDMETHODIMP accDoDefaultAction(VARIANT var_id);
Expand Down Expand Up @@ -101,86 +134,152 @@ class ATL_NO_VTABLE BrowserAccessibility
// Returns the value associated with the object.
STDMETHODIMP get_accValue(VARIANT var_id, BSTR* value);

// Non-supported (by WebKit) IAccessible methods.
STDMETHODIMP accSelect(LONG flags_sel, VARIANT var_id) { return E_NOTIMPL; }
// Make an object take focus or extend the selection.
STDMETHODIMP accSelect(LONG flags_sel, VARIANT var_id);

STDMETHODIMP get_accHelpTopic(BSTR* help_file,
VARIANT var_id,
LONG* topic_id);

STDMETHODIMP get_accSelection(VARIANT* selected);

// Deprecated functions, not implemented here.
STDMETHODIMP put_accName(VARIANT var_id, BSTR put_name) { return E_NOTIMPL; }
STDMETHODIMP put_accValue(VARIANT var_id, BSTR put_val) { return E_NOTIMPL; }
// Deprecated methods, not implemented.
STDMETHODIMP put_accName(VARIANT var_id, BSTR put_name) {
return E_NOTIMPL;
}
STDMETHODIMP put_accValue(VARIANT var_id, BSTR put_val) {
return E_NOTIMPL;
}

// Accessors/mutators.
HWND parent_hwnd() const { return parent_hwnd_;}
//
// IAccessible2 methods.
//

// Modify/retrieve the state (active/inactive) of this instance.
void set_instance_active(bool instance_active) {
instance_active_ = instance_active;
}
int instance_active() const { return instance_active_; }
// Returns role from a longer list of possible roles.
STDMETHODIMP role(LONG* role);

int routing_id() const { return routing_id_; }
// Returns the state bitmask from a larger set of possible states.
STDMETHODIMP get_states(AccessibleStates* states);

private:
// Creates a VARIANT that will reference the current accessibility
// object, not a child accessibility object.
VARIANT ChildSelfVariant() const {
VARIANT var;
V_VT(&var) = VT_I4;
V_I4(&var) = CHILDID_SELF;
return var;
}
// Get the unique ID of this object so that the client knows if it's
// been encountered previously.
STDMETHODIMP get_uniqueID(LONG* unique_id);

// Wrapper functions, calling through to singleton instance of
// BrowserAccessibilityManager.
// Get the window handle of the enclosing window.
STDMETHODIMP get_windowHandle(HWND* window_handle);

// Creates an instance of BrowserAccessibility, initializes it and sets the
// [iaccessible_id] and [parent_id].
STDMETHODIMP CreateInstance(REFIID iid,
int iaccessible_id,
void** interface_ptr);
// Get this object's index in its parent object.
STDMETHODIMP get_indexInParent(LONG* index_in_parent);

// Composes and sends a message for requesting needed accessibility
// information. Unused LONG input parameters should be NULL, and the VARIANT
// an empty, valid instance.
bool RequestAccessibilityInfo(int iaccessible_func_id,
VARIANT var_id,
LONG input1, LONG input2);
// IAccessible2 methods not implemented.
STDMETHODIMP get_extendedRole(BSTR* extended_role) {
return E_NOTIMPL;
}
STDMETHODIMP get_nRelations(LONG* n_relations) {
return E_NOTIMPL;
}
STDMETHODIMP get_relation(LONG relation_index,
IAccessibleRelation** relation) {
return E_NOTIMPL;
}
STDMETHODIMP get_relations(LONG max_relations,
IAccessibleRelation** relations,
LONG *n_relations) {
return E_NOTIMPL;
}
STDMETHODIMP scrollTo(enum IA2ScrollType scroll_type) {
return E_NOTIMPL;
}
STDMETHODIMP scrollToPoint(enum IA2CoordinateType coordinate_type,
LONG x,
LONG y) {
return E_NOTIMPL;
}
STDMETHODIMP get_groupPosition(LONG* group_level,
LONG* similar_items_in_group,
LONG* position_in_group) {
return E_NOTIMPL;
}
STDMETHODIMP get_localizedExtendedRole(BSTR* localized_extended_role) {
return E_NOTIMPL;
}
STDMETHODIMP get_nExtendedStates(LONG* n_extended_states) {
return E_NOTIMPL;
}
STDMETHODIMP get_extendedStates(LONG max_extended_states,
BSTR** extended_states,
LONG* n_extended_states) {
return E_NOTIMPL;
}
STDMETHODIMP get_localizedExtendedStates(LONG max_localized_extended_states,
BSTR** localized_extended_states,
LONG* n_localized_extended_states) {
return E_NOTIMPL;
}
STDMETHODIMP get_locale(IA2Locale* locale) {
return E_NOTIMPL;
}
STDMETHODIMP get_attributes(BSTR* attributes) {
return E_NOTIMPL;
}

//
// IServiceProvider methods.
//

// Accessors.
const WebAccessibility::OutParams& response();
STDMETHODIMP QueryService(REFGUID guidService, REFIID riid, void** object);

private:
// Many MSAA methods take a var_id parameter indicating that the operation
// should be performed on a particular child ID, rather than this object.
// This method tries to figure out the target object from |var_id| and
// returns a pointer to the target object if it exists, otherwise NULL.
// Does not return a new reference.
BrowserAccessibility* GetTargetFromChildID(const VARIANT& var_id);

// Returns a conversion from the BrowserAccessibilityRole (as defined in
// webkit/glue/webaccessibility.h) to an MSAA role.
long MSAARole(long browser_accessibility_role);
LONG MSAARole(LONG browser_accessibility_role);

// Returns a conversion from the BrowserAccessibilityState (as defined in
// webkit/glue/webaccessibility.h) to MSAA states set.
long MSAAState(long browser_accessibility_state);

// Id to uniquely distinguish this instance in the render-side caching,
// mapping it to the correct IAccessible on that side. Initialized to -1.
int iaccessible_id_;

// The unique ids of this IAccessible instance. Used to help
// BrowserAccessibilityManager instance retrieve the correct member
// variables for this process.
int routing_id_;
int process_id_;

HWND parent_hwnd_;

// The instance should only be active if there is a non-terminated
// RenderProcessHost associated with it. The BrowserAccessibilityManager keeps
// track of this state, and sets it to false to disable all calls into the
// renderer from this instance of BroweserAccessibility, and have all
// IAccessible functions return E_FAIL.
LONG MSAAState(LONG browser_accessibility_state);

// The manager of this tree of accessibility objects; needed for
// global operations like focus tracking.
BrowserAccessibilityManager* manager_;
// The parent of this object, may be NULL if we're the root object.
BrowserAccessibility* parent_;
// The ID of this object; globally unique within the browser process.
LONG child_id_;
// The index of this within its parent object.
LONG index_in_parent_;
// The ID of this object in the renderer process.
int32 renderer_id_;

// The children of this object.
std::vector<BrowserAccessibility*> children_;

// Accessibility metadata from the renderer, used to respond to MSAA
// events.
string16 name_;
string16 value_;
string16 action_;
string16 description_;
string16 help_;
string16 shortcut_;
LONG role_;
LONG state_;
WebKit::WebRect location_;

// COM objects are reference-counted. When we're done with this object
// and it's removed from our accessibility tree, a client may still be
// holding onto a pointer to this object, so we mark it as inactive
// so that calls to any of this object's methods immediately return
// failure.
bool instance_active_;

DISALLOW_COPY_AND_ASSIGN(BrowserAccessibility);
};

#endif // CHROME_BROWSER_BROWSER_ACCESSIBILITY_H_
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