Common up SVG transform "change detection" (classification)

third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.h

 /**
  * Copyright (C) 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Google, Inc.  All rights reserved.
  * 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
@@ skipping 112 matching lines @@
     SubtreeContentTransformScope(const AffineTransform&);
     ~SubtreeContentTransformScope();
 
     static AffineTransform currentContentTransformation() { return AffineTransform(s_currentContentTransformation); }
 
 private:
     static AffineTransform::Transform s_currentContentTransformation;
     AffineTransform m_savedContentTransformation;
 };
 
+// The following enumeration is used to optimize cases where the scale is known
+// to be invariant (see: LayoutSVGContainer::layout and LayoutSVGroot). The
+// value 'Full' can be used in the general case when the scale change is
+// unknown, or known to change.
+enum class SVGTransformChange {
+    None,
+    ScaleInvariant,
+    Full,
+};
+
+// Helper for computing ("classifying") a change to a transform using the
+// categoies defined above.
+class SVGTransformChangeDetector {
+    STACK_ALLOCATED();
+public:
+    explicit SVGTransformChangeDetector(const AffineTransform& previous)
+        : m_previousTransform(previous)
+    {
+    }
+
+    SVGTransformChange computeChange(const AffineTransform& current)
+    {
+        if (m_previousTransform == current)
+            return SVGTransformChange::None;
+        if (scaleReference(m_previousTransform) == scaleReference(current))
+            return SVGTransformChange::ScaleInvariant;
+        return SVGTransformChange::Full;
+    }
+
+private:
+    static std::pair<double, double> scaleReference(const AffineTransform& transform)
+    {
+        return std::make_pair(transform.xScaleSquared(), transform.yScaleSquared());
+    }
+    AffineTransform m_previousTransform;
+};
+
 template <typename LayoutObjectType>
 bool SVGLayoutSupport::computeHasNonIsolatedBlendingDescendants(const LayoutObjectType* object)
 {
     for (LayoutObject* child = object->firstChild(); child; child = child->nextSibling()) {
         if (child->isBlendingAllowed() && child->style()->hasBlendMode())
             return true;
         if (child->hasNonIsolatedBlendingDescendants() && !willIsolateBlendingDescendantsForObject(child))
             return true;
     }
     return false;
 }
 
 } // namespace blink
 
 #endif // SVGLayoutSupport_h