Implement basic parts of hit regions on canvas2d.

Source/core/accessibility/AXNodeObject.cpp

 /*
 * Copyright (C) 2012, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 1229 matching lines @@
 
     return String();
 }
 
 LayoutRect AXNodeObject::elementRect() const
 {
     // First check if it has a custom rect, for example if this element is tied to a canvas path.
     if (!m_explicitElementRect.isEmpty())
         return m_explicitElementRect;
 
+    if (node()->parentElement()->isInCanvasSubtree()) {

[dmazzoni, 2014/06/09 07:27:26]

OK for now, but add a FIXME indicating that this is inefficient if there are a
lot of elements in the canvas.

AXComputedObjectAttributeCache might be a good candidate for speeding this up.
Again, don't worry about fixing in this change but please make a note of it.

[zino, 2014/06/10 10:09:34]

Done.

+        LayoutRect rect;
+
+        for (Node* child = node()->firstChild(); child; child = child->nextSibling()) {
+            if (child->isHTMLElement()) {
+                if (AXObject* obj = axObjectCache()->get(child)) {
+                    if (rect.isEmpty())
+                        rect = obj->elementRect();
+                    else
+                        rect.unite(obj->elementRect());
+                }
+            }
+        }
+
+        return rect;

[dmazzoni, 2014/06/09 07:27:26]

If the resulting rect is still empty, fall through to the code below - a rect
somewhere in the canvas is much better than an empty rect.

[zino, 2014/06/10 10:09:34]

Done.

+    }
+
     // AXNodeObjects have no mechanism yet to return a size or position.

[dmazzoni, 2014/06/09 07:27:26]

Delete this first bit of the comment and change it to say, if this object
doesn't have an explicit element rect or one computable from its children,
return the position of the ancestor that does have...

[zino, 2014/06/10 10:09:34]

Done.

     // For now, let's return the position of the ancestor that does have a position,
     // and make it the width of that parent, and about the height of a line of text, so that it's clear the object is a child of the parent.
 
     LayoutRect boundingBox;
 
     for (AXObject* positionProvider = parentObject(); positionProvider; positionProvider = positionProvider->parentObject()) {
         if (positionProvider->isAXRenderObject()) {
             LayoutRect parentRect = positionProvider->elementRect();
             boundingBox.setSize(LayoutSize(parentRect.width(), LayoutUnit(std::min(10.0f, parentRect.height().toFloat()))));
             boundingBox.setLocation(parentRect.location());
@@ skipping 420 matching lines @@
     float range = maxValueForRange() - minValueForRange();
     float value = valueForRange();
 
     value += range * (percentChange / 100);
     setValue(String::number(value));
 
     axObjectCache()->postNotification(node(), AXObjectCache::AXValueChanged, true);
 }
 
 } // namespace WebCore