Implement closed shadow adjustment for Element.offsetParent

third_party/WebKit/Source/core/html/HTMLElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLElement.cpp b/third_party/WebKit/Source/core/html/HTMLElement.cpp
index 97f7595717213225f3016ec684e83d20fafde47f..7d232d27b792980f594d03353f394ffd3b571dda 100644
--- a/third_party/WebKit/Source/core/html/HTMLElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLElement.cpp
@@ -54,6 +54,7 @@
 #include "core/html/HTMLTemplateElement.h"
 #include "core/html/HTMLTextFormControlElement.h"
 #include "core/html/parser/HTMLParserIdioms.h"
+#include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutObject.h"
 #include "core/page/SpatialNavigation.h"
 #include "platform/Language.h"
@@ -1051,6 +1052,52 @@ const AtomicString& HTMLElement::eventParameterName()
     return eventString;
 }
 
+int HTMLElement::offsetLeftForBinding()
+{
+    document().updateStyleAndLayoutIgnorePendingStylesheetsForNode(this);
+    if (LayoutBoxModelObject* layoutObject = layoutBoxModelObject())
+        return adjustLayoutUnitForAbsoluteZoom(LayoutUnit(layoutObject->pixelSnappedOffsetLeft(unclosedOffsetParent())), layoutObject->styleRef()).round();
+    return 0;
+}
+
+int HTMLElement::offsetTopForBinding()
+{
+    document().updateStyleAndLayoutIgnorePendingStylesheetsForNode(this);
+    if (LayoutBoxModelObject* layoutObject = layoutBoxModelObject())
+        return adjustLayoutUnitForAbsoluteZoom(LayoutUnit(layoutObject->pixelSnappedOffsetTop(unclosedOffsetParent())), layoutObject->styleRef()).round();
+    return 0;
+}
+
+int HTMLElement::offsetWidthForBinding()
+{
+    document().updateStyleAndLayoutIgnorePendingStylesheetsForNode(this);
+    if (LayoutBoxModelObject* layoutObject = layoutBoxModelObject())
+        return adjustLayoutUnitForAbsoluteZoom(LayoutUnit(layoutObject->pixelSnappedOffsetWidth(unclosedOffsetParent())), layoutObject->styleRef()).round();
+    return 0;
+}
+
+int HTMLElement::offsetHeightForBinding()
+{
+    document().updateStyleAndLayoutIgnorePendingStylesheetsForNode(this);
+    if (LayoutBoxModelObject* layoutObject = layoutBoxModelObject())
+        return adjustLayoutUnitForAbsoluteZoom(LayoutUnit(layoutObject->pixelSnappedOffsetHeight(unclosedOffsetParent())), layoutObject->styleRef()).round();
+    return 0;
+}
+
+Element* HTMLElement::unclosedOffsetParent()
+{
+    document().updateStyleAndLayoutIgnorePendingStylesheetsForNode(this);
+
+    LayoutObject* layoutObject = this->layoutObject();
+    if (!layoutObject)
+        return nullptr;
+
+    Element* element = layoutObject->offsetParent();
+    while (element && (!element->isUnclosedNodeOf(*this) || (element->isInShadowTree() && element->containingShadowRoot()->type() == ShadowRootType::UserAgent)))

[hayato, 2016/06/27 06:58:32]

I do not think it is a good idea to loop here by calling offsetParent
repeatedly.
This loop should be merged into a LayoutObject::offsetParent itself.

Unless that, I am afraid that this would not be a spec compliant.

Also, is there any way to avoid calling isUnclosdeNodeOf repeatedly in each
loop?
If there is, it would be nice.

[kochi, 2016/06/28 07:59:59]

That will break LayoutObject::offsetParent, as you already commented previously.

To be spec compliant, all the dependency is isolated here to keep existing
Element::offsetParent() and LayoutObject::offsetParent() users working.
All the HTMLElement.offsetParent()-relative offsets are done in this file
(e.g. HTMLElement::offsetTopForBinding() etc.)

We could have LayoutObject::unclosedOffsetParent(), but it doesn't improve any
performance because it would use the same loop here.
That's a valid concern, but for most cases isUnclosedNodeOf() is called only
once,
so the additional cost for offsetParent should not be significant on average.

In cases where repeated calls are necessary (the element is distributed deep
under
shadow trees), this could be optimized so that only the first unclosed node
(probably
the shadow host of the element) and above are searched, but I may miss some
conditions, and need to give more thought on possible cases.

I added a TODO comment here to note that it is possible to a performance hit.

+        element = element->layoutObject()->offsetParent();
+    return element;
+}
+
 } // namespace blink
 
 #ifndef NDEBUG