CSS: SVG use elements replicate updates to style

third_party/WebKit/Source/core/dom/Node.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 71 matching lines @@
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/html/HTMLDialogElement.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/html/HTMLSlotElement.h"
 #include "core/input/EventHandler.h"
 #include "core/inspector/InstanceCounters.h"
 #include "core/layout/LayoutBox.h"
 #include "core/page/ContextMenuController.h"
 #include "core/page/Page.h"
+#include "core/svg/SVGElement.h"
+#include "core/svg/SVGUseElement.h"
 #include "core/svg/graphics/SVGImage.h"
 #include "platform/EventDispatchForbiddenScope.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/TraceEvent.h"
 #include "platform/TracedValue.h"
 #include "wtf/HashSet.h"
 #include "wtf/Vector.h"
 #include "wtf/allocator/Partitions.h"
 #include "wtf/text/CString.h"
 #include "wtf/text/StringBuilder.h"
@@ skipping 591 matching lines @@
         TRACE_DISABLED_BY_DEFAULT("devtools.timeline.invalidationTracking"),
         "StyleRecalcInvalidationTracking",
         TRACE_EVENT_SCOPE_THREAD,
         "data",
         InspectorStyleRecalcInvalidationTrackingEvent::data(this, reason));
 
     StyleChangeType existingChangeType = getStyleChangeType();
     if (changeType > existingChangeType)
         setStyleChange(changeType);
 
-    if (existingChangeType == NoStyleChange)
-        markAncestorsWithChildNeedsStyleRecalc();
-
     if (isElementNode() && hasRareData())
         toElement(*this).setAnimationStyleChange(false);
+
+    if (existingChangeType != NoStyleChange)
+        return;
+    markAncestorsWithChildNeedsStyleRecalc();
+    if (!isSVGElement())
+        return;

[rune, 2016/08/18 21:15:28]

I think I'd move the code below into a separate method on SVGElement.

[Eric Willigers, 2016/08/18 22:27:00]

Done.

+    const HeapHashSet<WeakMember<SVGElement>>& set = toSVGElement(this)->instancesForElement();
+    if (set.isEmpty())
+        return;
+    for (SVGElement* instance : set) {
+        if (SVGUseElement* element = instance->correspondingUseElement())
+            element->setNeedsStyleRecalc(SubtreeStyleChange, reason);

[rune, 2016/08/18 21:09:07]

So there's an 1:n relationship between each svg element in the original subtree
and each and every svg element copy in the use shadow trees?

Could we make this cheaper than SubtreeStyleChange on the <use> element? Would
it be incorrect to just set the StyleChangeType on the specific instances
instead of nuking style for the the whole subtree for every change?

It's not possible to modify the use shadow tree to be different from the
referenced subtree, right?

IIUC, the computed styles for the copied subtree might be different because the
"used" elements will inherit from the <use> element. Is that right?

[fs, 2016/08/18 21:21:17]

Yes.
I was hoping we could do something like that. Haven't been able to come up with
a counter-example to that, but maybe Eric has?
Correct.
Yes.

[Eric Willigers, 2016/08/18 22:27:00]

Done. All my tests still pass. I should have tried it earlier.

+    }
 }
 
 void Node::clearNeedsStyleRecalc()
 {
     m_nodeFlags &= ~StyleChangeMask;
 
     clearSVGFilterNeedsLayerUpdate();
 
     if (isElementNode() && hasRareData())
         toElement(*this).setAnimationStyleChange(false);
@@ skipping 1678 matching lines @@
 
 void showNodePath(const blink::Node* node)
 {
     if (node)
         node->showNodePathForThis();
     else
         fprintf(stderr, "Cannot showNodePath for (nil)\n");
 }
 
 #endif