More targeted resource-switching mechanism for SVG selection painting

third_party/WebKit/Source/core/layout/svg/SVGResourcesCache.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 168 matching lines @@
 void SVGResourcesCache::ClientDestroyed(LayoutObject* layout_object) {
   DCHECK(layout_object);
 
   SVGResources* resources = CachedResourcesForLayoutObject(layout_object);
   if (resources)
     resources->RemoveClientFromCache(layout_object);
   SVGResourcesCache& cache = ResourcesCache(layout_object->GetDocument());
   cache.RemoveResourcesFromLayoutObject(layout_object);
 }
 
+SVGResourcesCache::TemporaryStyleScope::TemporaryStyleScope(
+    LayoutObject& layout_object,
+    const ComputedStyle& style,
+    const ComputedStyle& temporary_style)
+    : layout_object_(layout_object),
+      original_style_(style),
+      styles_are_equal_(style == temporary_style) {
+  SwitchTo(temporary_style);
+}
+
+void SVGResourcesCache::TemporaryStyleScope::SwitchTo(
+    const ComputedStyle& style) {
+  DCHECK(LayoutObjectCanHaveResources(&layout_object_));
+  if (styles_are_equal_)
+    return;
+  SVGResourcesCache& cache = ResourcesCache(layout_object_.GetDocument());
+  cache.RemoveResourcesFromLayoutObject(&layout_object_);
+  cache.AddResourcesFromLayoutObject(&layout_object_, style);

[Stephen Chennney, 2017/04/28 16:16:40]

A non-trivial chunk of invalidation logic is gone now. I presume that's a good
things because we do not want any invalidation for this style change. Am I
right?

[fs, 2017/04/28 18:16:34]

That is correct. Optimally we'd like to just produce fill/stroke (as needed)
from the selection style and use that - without any side-effects. As things are
right now, we rely on the 1:1 mapping LayoutObject<->SVGResources, and this is
submerged in the "fetch <paint>" code (i.e goes through the HashMap), so we need
to swap out the SVGResources. (Unfortunately this swaps out more than we'd want,
hence the dependent CLs.)
The invalidation bit on the other hand does us no good (since we're not actually
mutating the element/LayoutObject.)

+}
+
 }  // namespace blink