Optimize glyph positioning for SVG <textPath> layout

Source/platform/graphics/Path.h

 /*
  * Copyright (C) 2003, 2006, 2009 Apple Inc. All rights reserved.
  *               2006 Rob Buis <buis@kde.org>
  * Copyright (C) 2007-2008 Torch Mobile, Inc.
  * Copyright (C) 2013 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
@@ skipping 15 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef Path_h
 #define Path_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/RoundedRect.h"
 #include "platform/graphics/WindRule.h"
 #include "third_party/skia/include/core/SkPath.h"
+#include "third_party/skia/include/core/SkPathMeasure.h"
 #include "wtf/FastAllocBase.h"
 #include "wtf/Forward.h"
 
 class SkPath;
 
 namespace WebCore {
 
 class AffineTransform;
 class FloatPoint;
 class FloatRect;
@@ skipping 32 matching lines @@
     bool contains(const FloatPoint&, WindRule = RULE_NONZERO) const;
     bool strokeContains(const FloatPoint&, const StrokeData&) const;
     FloatRect boundingRect() const;
     FloatRect strokeBoundingRect(const StrokeData&) const;
 
     float length() const;
     FloatPoint pointAtLength(float length, bool& ok) const;
     float normalAngleAtLength(float length, bool& ok) const;
     bool pointAndNormalAtLength(float length, FloatPoint&, float&) const;
 
+    // Helper for computing a sequence of positions and normals (normal angles) on a path.
+    // The best possible access pattern will be one where the |length| value is
+    // strictly increasing.
+    // For other access patterns, performance will vary depending on curvature
+    // and number of segments, but should never be worse than that of the
+    // state-less method on Path.
+    class PLATFORM_EXPORT PositionCalculator {
+        WTF_MAKE_NONCOPYABLE(PositionCalculator);
+    public:
+        explicit PositionCalculator(const Path&);
+
+        bool pointAndNormalAtLength(float length, FloatPoint&, float&);
+
+    private:
+        SkPath m_path;
+        SkPathMeasure m_pathMeasure;
+        SkScalar m_accumulatedLength;
+    };
+
     void clear();
     bool isEmpty() const;
     // Gets the current point of the current path, which is conceptually the final point reached by the path so far.
     // Note the Path can be empty (isEmpty() == true) and still have a current point.
     bool hasCurrentPoint() const;
     FloatPoint currentPoint() const;
 
     WindRule windRule() const;
     void setWindRule(const WindRule);
 
@@ skipping 32 matching lines @@
     SkPath m_path;
 };
 
 #if !ASSERT_DISABLED
 PLATFORM_EXPORT bool ellipseIsRenderable(float startAngle, float endAngle);
 #endif
 
 }
 
 #endif