accessible/src/base/nsAccessibleTreeWalker.cpp
author David Bolter <dbolter@mozilla.com>
Mon, 01 Feb 2010 21:27:32 -0500
changeset 37808 fb6bebbcf7f3bf781c58ac3afa7abc57210a4c83
parent 35583 1f455848b0863354324809e341575450d477106f
permissions -rw-r--r--
Bug 542221 - DeCOMtaminate some usage of nsAccessibilityService. r=surkov

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 2003
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Original Author: Aaron Leventhal (aaronl@netscape.com)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#include "nsAccessibleTreeWalker.h"

#include "nsAccessibilityAtoms.h"
#include "nsAccessNode.h"

#include "nsIAnonymousContentCreator.h"
#include "nsIServiceManager.h"
#include "nsIContent.h"
#include "nsIDOMXULElement.h"
#include "nsIPresShell.h"
#include "nsAccessibilityService.h"
#include "nsWeakReference.h"

nsAccessibleTreeWalker::nsAccessibleTreeWalker(nsIWeakReference* aPresShell, nsIDOMNode* aNode, PRBool aWalkAnonContent): 
  mWeakShell(aPresShell),
  mWalkAnonContent(aWalkAnonContent)
{
  mState.domNode = aNode;
  mState.prevState = nsnull;
  mState.siblingIndex = eSiblingsUninitialized;
  mState.siblingList = nsnull;
  mState.isHidden = false;

  MOZ_COUNT_CTOR(nsAccessibleTreeWalker);
}

nsAccessibleTreeWalker::~nsAccessibleTreeWalker()
{
  // Clear state stack from memory
  while (NS_SUCCEEDED(PopState()))
    /* do nothing */ ;
   MOZ_COUNT_DTOR(nsAccessibleTreeWalker);
}

void nsAccessibleTreeWalker::GetKids(nsIDOMNode *aParentNode)
{
  nsCOMPtr<nsIContent> parentContent(do_QueryInterface(aParentNode));
  if (!parentContent || !parentContent->IsHTML()) {
    mState.frame = nsnull;  // Don't walk frames in non-HTML content, just walk the DOM.
  }

  WalkFrames();

  // Walk frames? UpdateFrame() sets this when it sees anonymous frames
  if (mState.siblingIndex == eSiblingsWalkFrames) {
    return;
  }

  // Walk anonymous content? Not currently used for HTML -- anonymous content there uses frame walking
  mState.siblingIndex = 0;   // Indicates our index into the sibling list
  if (parentContent) {
    if (mWalkAnonContent) {
      // Walk anonymous content
      nsIDocument* doc = parentContent->GetOwnerDoc();
      if (doc) {
        // returns null if no anon nodes
        doc->GetXBLChildNodesFor(parentContent,
                                 getter_AddRefs(mState.siblingList));
      }
    }
    if (!mState.siblingList) {
      // Walk normal DOM. Just use nsIContent -- it doesn't require 
      // the mallocs that GetChildNodes() needs
      //aParentNode->GetChildNodes(getter_AddRefs(mState.siblingList));
      mState.parentContent = parentContent;
      mState.domNode = do_QueryInterface(parentContent->GetChildAt(0 /* 0 == mState.siblingIndex */));
      return;
    }
  }
  else {
    // We're on document node, that's why we could not QI to nsIContent.
    // So, use nsIDOMNodeList method to walk content.
    aParentNode->GetChildNodes(getter_AddRefs(mState.siblingList));
    if (!mState.siblingList) {
      return;
    }
  }

  mState.siblingList->Item(0 /* 0 == mState.siblingIndex */, getter_AddRefs(mState.domNode));
}

NS_IMETHODIMP nsAccessibleTreeWalker::PopState()
{
  nsIFrame *frameParent =
    mState.frame.GetFrame() ? mState.frame.GetFrame()->GetParent() : nsnull;
  if (mState.prevState) {
    WalkState *toBeDeleted = mState.prevState;
    mState = *mState.prevState; // deep copy
    mState.isHidden = PR_FALSE; // If we were in a child, the parent wasn't hidden
    if (!mState.frame.GetFrame()) {
      mState.frame = frameParent;
    }
    delete toBeDeleted;
    return NS_OK;
  }
  ClearState();
  mState.frame = frameParent;
  mState.isHidden = PR_FALSE;
  return NS_ERROR_FAILURE;
}

void nsAccessibleTreeWalker::ClearState()
{
  mState.siblingList = nsnull;
  mState.parentContent = nsnull;
  mState.accessible = nsnull;
  mState.domNode = nsnull;
  mState.siblingIndex = eSiblingsUninitialized;
}

NS_IMETHODIMP nsAccessibleTreeWalker::PushState()
{
  // Duplicate mState and put right before end; reset mState; make mState the new end of the stack
  WalkState* nextToLastState= new WalkState();
  if (!nextToLastState)
    return NS_ERROR_OUT_OF_MEMORY;
  *nextToLastState = mState;  // Deep copy - copy contents of struct to new state that will be added to end of our stack
  ClearState();
  mState.prevState = nextToLastState;   // Link to previous state
  return NS_OK;
}

void nsAccessibleTreeWalker::GetNextDOMNode()
{
  // Get next DOM node and its frame.
  if (mState.parentContent) {
    mState.domNode =
      do_QueryInterface(mState.parentContent->GetChildAt(++mState.siblingIndex));

  } else if (mState.siblingIndex == eSiblingsWalkFrames) {
    if (mState.frame.IsAlive()) {
      mState.frame = mState.frame.GetFrame()->GetNextSibling();

      if (mState.frame.IsAlive()) {
        mState.domNode = do_QueryInterface(mState.frame.GetFrame()->GetContent());
        return;
      }
    }

    mState.domNode = nsnull;
    return;

  } else {
    mState.siblingList->Item(++mState.siblingIndex,
                             getter_AddRefs(mState.domNode));
  }

  // Update the frame.
  nsCOMPtr<nsIPresShell> presShell(do_QueryReferent(mWeakShell));
  NS_ASSERTION(presShell, "Huh? No presshell?");
  if (!presShell)
    return;

  nsCOMPtr<nsIContent> content = do_QueryInterface(mState.domNode);
  if (content)
    mState.frame = presShell->GetRealPrimaryFrameFor(content);
  else
    mState.frame = presShell->GetRootFrame();
}

NS_IMETHODIMP nsAccessibleTreeWalker::GetNextSibling()
{
  // Make sure mState.prevState and mState.siblingIndex are initialized so we can walk forward
  NS_ASSERTION(mState.prevState && mState.siblingIndex != eSiblingsUninitialized,
               "Error - GetNextSibling() only works after a GetFirstChild(), so we must have a prevState.");
  mState.accessible = nsnull;

  while (PR_TRUE) {
    // Get next frame
    GetNextDOMNode();

    if (!mState.domNode) {  // Done with current siblings
      PopState();   // Use parent - go up in stack. Can always pop state because we have to start with a GetFirstChild().
      if (!mState.prevState) {
        mState.accessible = nsnull;
        break; // Back to original accessible that we did GetFirstChild() from
      }
    }
    else if ((mState.domNode != mState.prevState->domNode && GetAccessible()) || 
             NS_SUCCEEDED(GetFirstChild())) {
      return NS_OK; // if next is accessible, use it 
    }
  }
  return NS_ERROR_FAILURE;
}

NS_IMETHODIMP nsAccessibleTreeWalker::GetFirstChild()
{
  mState.accessible = nsnull;
  if (mState.isHidden || !mState.domNode) {
    return NS_ERROR_FAILURE;
  }

  nsCOMPtr<nsIDOMNode> parent(mState.domNode);

  PushState();
  GetKids(parent); // Side effects change our state (mState)

  // Recursive loop: depth first search for first accessible child
  while (mState.domNode) {
    if ((mState.domNode != parent && GetAccessible()) || NS_SUCCEEDED(GetFirstChild()))
      return NS_OK;

    GetNextDOMNode();
  }

  PopState();  // Return to previous state
  return NS_ERROR_FAILURE;
}

void 
nsAccessibleTreeWalker::WalkFrames()
{
  nsIFrame *curFrame = mState.frame.GetFrame();
  if (!curFrame) {
    return;
  }

  // If the frame implements nsIAnonymousContentCreator interface then go down
  // through the frames and obtain anonymous nodes for them.
  nsIAnonymousContentCreator* creator = do_QueryFrame(curFrame);
  nsIFrame *child = curFrame->GetFirstChild(nsnull);

  if (creator && child && mState.siblingIndex < 0) {
    mState.frame = child;
    mState.domNode = do_QueryInterface(child->GetContent());
    mState.siblingIndex = eSiblingsWalkFrames;
  }
// temporary workaround for Bug 359210. We never want to walk frames.
// Aaron Leventhal will refix :before and :after content later without walking frames.
#if 0
  if (mState.frame && mState.siblingIndex < 0) {
    // Container frames can contain generated content frames from
    // :before and :after style rules, so we walk their frame trees
    // instead of content trees
    // XXX Walking the frame tree doesn't get us Aural CSS nodes, e.g. 
    // @media screen { display: none; }
    // Asking the style system might be better (with ProbePseudoStyleFor(),
    // except that we need to ask only for those display types that support 
    // :before and :after (which roughly means non-replaced elements)
    // Here's some code to see if there is an :after rule for an element
    // nsRefPtr<nsStyleContext> pseudoContext;
    // nsStyleContext *styleContext = primaryFrame->GetStyleContext();
    // if (aContent) {
    //   pseudoContext = presContext->StyleSet()->
    //     ProbePseudoStyleFor(content, nsAccessibilityAtoms::after, aStyleContext);
    mState.domNode = do_QueryInterface(mState.frame->GetContent());
    mState.siblingIndex = eSiblingsWalkFrames;
  }
#endif
}

/**
 * If the DOM node's frame has an accessible or the DOMNode
 * itself implements nsIAccessible return it.
 */
PRBool nsAccessibleTreeWalker::GetAccessible()
{
  mState.accessible = nsnull;
  nsCOMPtr<nsIPresShell> presShell(do_QueryReferent(mWeakShell));

  GetAccService()->GetAccessible(mState.domNode, presShell, mWeakShell,
                                 mState.frame.GetFrame(), &mState.isHidden,
                                 getter_AddRefs(mState.accessible));

  return mState.accessible ? PR_TRUE : PR_FALSE;
}