Fix accessibility coordinates within iframes.

content/browser/accessibility/browser_accessibility.cc

Index: content/browser/accessibility/browser_accessibility.cc
diff --git a/content/browser/accessibility/browser_accessibility.cc b/content/browser/accessibility/browser_accessibility.cc
index 857a1619baaf2014b565d74e6e5945fca36dd234..7484ced00aebba56d0efa40659abca817a94c3d2 100644
--- a/content/browser/accessibility/browser_accessibility.cc
+++ b/content/browser/accessibility/browser_accessibility.cc
@@ -133,15 +133,30 @@ BrowserAccessibility* BrowserAccessibility::GetNextSibling() {
 gfx::Rect BrowserAccessibility::GetLocalBoundsRect() {
   gfx::Rect bounds = location_;
 
-  // Adjust top left position by the root document's scroll offset.
-  BrowserAccessibility* root = manager_->GetRoot();
-  int scroll_x = 0;
-  int scroll_y = 0;
-  if (!root->GetIntAttribute(AccessibilityNodeData::ATTR_SCROLL_X, &scroll_x) ||
-      !root->GetIntAttribute(AccessibilityNodeData::ATTR_SCROLL_Y, &scroll_y)) {
-    return bounds;
+  // Walk up the parent chain. Every time we encounter a Web Area, offset
+  // based on the scroll bars and then offset based on the origin of that
+  // nested web area.
+  BrowserAccessibility* parent = parent_;
+  bool need_to_offset_web_area =

[aboxhall, 2013/01/29 01:52:40]

I don't completely follow this. Why do we need to offset the bounds if |this| is
a WebArea? Or am I not reading this correctly?

[dmazzoni, 2013/01/29 16:51:50]

We need to offset the bounds of the first parent of a WebArea - the bool is  set
last, checked first.

A WebArea will be in local coordinates - like (0,0) - (300, 100). So we need to
offset by the first parent of the WebArea, but skip over nodes that have no
width and height, that's probably a bug.

[aboxhall, 2013/01/29 17:43:26]

So a WebArea will have its _own_ coordinates in terms of its local frame, rather
than the containing one?

Obviously this code works, I just don't understand why.

[dmazzoni, 2013/01/29 18:51:25]

Yeah, internally the tree looks something like:

DIV x=0 y=0     width=300 height=100
    BUTTON ...
DIV x=0 y=100 width=300 height=100
    BUTTON ...
DIV x=0 y=200 width=300 height=100
    IFRAME x=0 y=200 width=300 height=100
        DOCUMENT x=0 y=0 width=300 height=100
            DIV x=0 y=0 width=300 height=100
                BUTTON ...

So the iframe element is one of the containers of the web area, and it's in the
coordinates of the outer frame. The web area is the root document of the inner
frame - so it's in local coordinates.

So when computing the coordinates of an element, as you walk up the parent chain
the algorithm is: when you reach a webarea role (a document element), add the
top/left of the NEXT parent you find while walking up, to transform to local
coordinates of the outer frame.

[aboxhall, 2013/01/29 19:53:47]

Got it, thanks for the explanation.

+      (role_ == AccessibilityNodeData::ROLE_WEB_AREA);
+  while (parent) {
+    if (need_to_offset_web_area &&
+        parent->location().width() > 0 &&
+        parent->location().height() > 0) {
+      bounds.Offset(parent->location().x(), parent->location().y());
+      need_to_offset_web_area = false;
+    }
+    if (parent->role() == AccessibilityNodeData::ROLE_WEB_AREA) {
+      int sx = 0;
+      int sy = 0;
+      if (parent->GetIntAttribute(AccessibilityNodeData::ATTR_SCROLL_X, &sx) &&
+          parent->GetIntAttribute(AccessibilityNodeData::ATTR_SCROLL_Y, &sy)) {
+        bounds.Offset(-sx, -sy);
+      }
+      need_to_offset_web_area = true;
+    }
+    parent = parent->parent();
   }
-  bounds.Offset(-scroll_x, -scroll_y);
 
   return bounds;
 }