Bug 388927 - getChildAtPoint fails for scrolled content, r=evan.yan, roc, sr=roc, a=dsicore

accessible/src/base/nsAccessible.cpp

@@ -1082,70 +1082,73 @@ NS_IMETHODIMP nsAccessible::GetFocusedChild(nsIAccessible **aFocusedChild)
 }
 
   /* nsIAccessible getChildAtPoint (in long x, in long y); */
-NS_IMETHODIMP nsAccessible::GetChildAtPoint(PRInt32 tx, PRInt32 ty, nsIAccessible **aAccessible)
+NS_IMETHODIMP
+nsAccessible::GetChildAtPoint(PRInt32 aX, PRInt32 aY,
+                              nsIAccessible **aAccessible)
 {
+  NS_ENSURE_ARG_POINTER(aAccessible);
   *aAccessible = nsnull;
 
-  nsCOMPtr<nsIAccessible> child;
-  GetFirstChild(getter_AddRefs(child));
+  // Search an accessible at the given point starting from accessible document
+  // because containing block (see CSS2) for out of flow element (for example,
+  // absolutely positioned element) may be different from its DOM parent and
+  // therefore accessible for containing block may be different from accessible
+  // for DOM parent but GetFrameForPoint() should be called for containing block
+  // to get an out of flow element.
+  nsCOMPtr<nsIAccessibleDocument> accDocument;
+  nsresult rv = GetAccessibleDocument(getter_AddRefs(accDocument));
+  NS_ENSURE_SUCCESS(rv, rv);
 
-  PRInt32 x, y, w, h;
-  PRUint32 state;
-
-  nsCOMPtr<nsIAccessible> childAtPoint;
-  while (child) {
-    child->GetBounds(&x, &y, &w, &h);
-    if (tx >= x && tx < x + w && ty >= y && ty < y + h) {
-      nsCOMPtr<nsPIAccessNode> accessNode(do_QueryInterface(child));
-      if (accessNode) {
-        nsIFrame *frame = accessNode->GetFrame();
-        if (!frame) {
-          state = State(child);
-          // In some cases accessibles don't have a frame; examples are
-          // tree items or combo box dropdown markers. For these cases
-          // just ensure that the returned accessible is visible.
-          if ((state & (nsIAccessibleStates::STATE_OFFSCREEN |
-              nsIAccessibleStates::STATE_INVISIBLE)) == 0) {
-            // Don't walk into offscreen or invisible items
-            NS_IF_ADDREF(*aAccessible = child);
-            return NS_OK;
-          }
-        }
-        else {
-          // If there are multiple accessibles the contain the point 
-          // and they overlap then pick the one with a frame that contains the point
-          // For example, A point that's in block #2 is also in block #1, but we want to return #2:
-          // [[block #1 is long wrapped text that continues to
-          // another line]]  [[here is a shorter block #2]]
-          while (frame) {
-            if (frame->GetScreenRectExternal().Contains(tx, ty)) {
-              childAtPoint = child;
-              break; // Definitely in this accessible, since one of its frame matches the point
-            }
-            frame = frame->GetNextContinuation();
-          }
-        }
-      }
-    }
-    nsCOMPtr<nsIAccessible> next;
-    child->GetNextSibling(getter_AddRefs(next));
-    child = next;
-  }
-
-  if (childAtPoint) {
-    NS_ADDREF(*aAccessible = childAtPoint);
+  if (!accDocument)
     return NS_OK;
-  }
-  GetState(&state, nsnull);
-  GetBounds(&x, &y, &w, &h);
-  if ((state & (nsIAccessibleStates::STATE_OFFSCREEN |
-                nsIAccessibleStates::STATE_INVISIBLE)) == 0 &&
-      tx >= x && tx < x + w && ty >= y && ty < y + h) {
-    *aAccessible = this;
-    NS_ADDREF_THIS();
+
+  nsCOMPtr<nsPIAccessNode> accessNodeDocument(do_QueryInterface(accDocument));
+  NS_ASSERTION(accessNodeDocument,
+               "nsIAccessibleDocument doesn't implement nsPIAccessNode");
+
+  nsIFrame *frame = accessNodeDocument->GetFrame();
+  NS_ENSURE_STATE(frame);
+
+  nsPresContext *presContext = frame->PresContext();
+
+  nsIntRect screenRect = frame->GetScreenRectExternal();
+  nsPoint offset(presContext->DevPixelsToAppUnits(aX - screenRect.x),
+                 presContext->DevPixelsToAppUnits(aY - screenRect.y));
+
+  nsCOMPtr<nsIPresShell> presShell = presContext->PresShell();
+  nsIFrame *foundFrame = presShell->GetFrameForPoint(frame, offset);
+  if (!foundFrame)
     return NS_OK;
+
+  nsCOMPtr<nsIContent> content(foundFrame->GetContent());
+  if (!content)
+    return NS_OK;
+
+  nsCOMPtr<nsIDOMNode> node(do_QueryInterface(content));
+  nsCOMPtr<nsIAccessibilityService> accService = GetAccService();
+
+  nsCOMPtr<nsIDOMNode> relevantNode;
+  accService->GetRelevantContentNodeFor(node, getter_AddRefs(relevantNode));
+  if (!relevantNode)
+    return NS_OK;
+
+  nsCOMPtr<nsIAccessible> accessible;
+  accService->GetAccessibleFor(relevantNode, getter_AddRefs(accessible));
+  if (!accessible)
+    return NS_OK;
+
+  nsCOMPtr<nsIAccessible> parent;
+  accessible->GetParent(getter_AddRefs(parent));
+
+  while (parent && parent != this) {
+    accessible.swap(parent);
+    accessible->GetParent(getter_AddRefs(parent));
   }
-  return NS_ERROR_FAILURE;
+
+  if (parent)
+    NS_ADDREF(*aAccessible = accessible);
+
+  return NS_OK;
 }
 
 void nsAccessible::GetBoundsRect(nsRect& aTotalBounds, nsIFrame** aBoundingFrame)

accessible/src/xul/nsXULTreeAccessible.cpp

@@ -319,6 +319,42 @@ NS_IMETHODIMP nsXULTreeAccessible::GetFocusedChild(nsIAccessible **aFocusedChild
   return NS_OK;
 }
 
+// nsIAccessible::getChildAtPoint(in long x, in long y)
+NS_IMETHODIMP
+nsXULTreeAccessible::GetChildAtPoint(PRInt32 aX, PRInt32 aY,
+                                     nsIAccessible **aAccessible)
+{
+  nsIFrame *frame = GetFrame();
+  if (!frame)
+    return NS_ERROR_FAILURE;
+
+  nsPresContext *presContext = frame->PresContext();
+  nsCOMPtr<nsIPresShell> presShell = presContext->PresShell();
+
+  nsIFrame *rootFrame = presShell->GetRootFrame();
+  NS_ENSURE_STATE(rootFrame);
+
+  nsIntRect rootRect = rootFrame->GetScreenRectExternal();
+
+  PRInt32 clientX = presContext->AppUnitsToIntCSSPixels(
+    presContext->DevPixelsToAppUnits(aX - rootRect.x));
+  PRInt32 clientY = presContext->AppUnitsToIntCSSPixels(
+    presContext->DevPixelsToAppUnits(aY - rootRect.y));
+
+  PRInt32 row = -1;
+  nsCOMPtr<nsITreeColumn> column;
+  nsCAutoString childEltUnused;
+  mTree->GetCellAt(clientX, clientY, &row, getter_AddRefs(column),
+                   childEltUnused);
+
+  // If we failed to find tree cell for the given point then it might be
+  // tree columns.
+  if (row == -1 || !column)
+    return nsXULSelectableAccessible::GetChildAtPoint(aX, aY, aAccessible);
+
+  return GetCachedTreeitemAccessible(row, column, aAccessible);
+}
+
 // Ask treeselection to get all selected children
 NS_IMETHODIMP nsXULTreeAccessible::GetSelectedChildren(nsIArray **_retval)
 {

accessible/src/xul/nsXULTreeAccessible.h

@@ -72,6 +72,8 @@ public:
   NS_IMETHOD GetLastChild(nsIAccessible **_retval);
   NS_IMETHOD GetChildCount(PRInt32 *_retval);
   NS_IMETHOD GetFocusedChild(nsIAccessible **aFocusedChild);
+  NS_IMETHOD GetChildAtPoint(PRInt32 aX, PRInt32 aY,
+                             nsIAccessible **aAccessible);
 
   static void GetTreeBoxObject(nsIDOMNode* aDOMNode, nsITreeBoxObject** aBoxObject);
   static nsresult GetColumnCount(nsITreeBoxObject* aBoxObject, PRInt32 *aCount);

layout/base/nsIPresShell.h

@@ -607,6 +607,14 @@ public:
    */
   virtual nsresult ReconstructFrames() = 0;
 
+  /**
+   * Given aFrame, the root frame of a stacking context, find its descendant
+   * frame under the point aPt that receives a mouse event at that location,
+   * or nsnull if there is no such frame.
+   * @param aPt the point, relative to the frame origin
+   */
+  virtual nsIFrame* GetFrameForPoint(nsIFrame* aFrame, nsPoint aPt) = 0;
+
   /**
    * See if reflow verification is enabled. To enable reflow verification add
    * "verifyreflow:1" to your NSPR_LOG_MODULES environment variable

layout/base/nsPresShell.cpp

@@ -873,7 +873,9 @@ public:
   virtual nsresult ReconstructFrames(void);
   virtual void Freeze();
   virtual void Thaw();
-  
+
+  virtual nsIFrame* GetFrameForPoint(nsIFrame* aFrame, nsPoint aPt);
+
   NS_IMETHOD RenderDocument(const nsRect& aRect, PRBool aUntrusted,
                             PRBool aIgnoreViewportScrolling,
                             nscolor aBackgroundColor,
@@ -2970,6 +2972,12 @@ PresShell::GetPageSequenceFrame(nsIPageSequenceFrame** aResult) const
   return *aResult ? NS_OK : NS_ERROR_FAILURE;
 }
 
+nsIFrame*
+PresShell::GetFrameForPoint(nsIFrame* aFrame, nsPoint aPt)
+{
+  return nsLayoutUtils::GetFrameForPoint(aFrame, aPt);
+}
+
 void
 PresShell::BeginUpdate(nsIDocument *aDocument, nsUpdateType aUpdateType)
 {