Improve performance of GeometryMapper cache.

third_party/WebKit/Source/platform/graphics/paint/GeometryMapperClipCache.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef GeometryMapperClipCache_h
+#define GeometryMapperClipCache_h
+
+#include "platform/PlatformExport.h"
+#include "platform/graphics/paint/FloatClipRect.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+class ClipPaintPropertyNode;
+class FloatClipRect;
+class TransformPaintPropertyNode;
+
+// A GeometryMapperClipCache hangs off a ClipPaintPropertyNode. It stores
+// cached "clip visual rects" (See GeometryMapper.h) from that node in
+// ancestor spaces.
+class PLATFORM_EXPORT GeometryMapperClipCache {
+ public:
+  GeometryMapperClipCache();
+
+  struct ClipAndTransform {
+    const ClipPaintPropertyNode* ancestorClip;
+    const TransformPaintPropertyNode* ancestorTransform;
+    bool operator==(const ClipAndTransform& other) const {
+      return ancestorClip == other.ancestorClip &&
+             ancestorTransform == other.ancestorTransform;
+    }
+    ClipAndTransform(const ClipPaintPropertyNode* ancestorClipArg,
+                     const TransformPaintPropertyNode* ancestorTransformArg)
+        : ancestorClip(ancestorClipArg),
+          ancestorTransform(ancestorTransformArg) {}
+  };
+
+  // Returns the clip visual rect  of the owning
+  // clip of |this| in the space of |ancestors|, if there is one cached.
+  // Otherwise returns null.
+  const FloatClipRect* getCachedClip(const ClipAndTransform& ancestors);
+  // Stores the "clip visual rect" of |this in the space of |ancestors|,
+  // into a local cache.
+
+  void setCachedClip(const ClipAndTransform&, const FloatClipRect&);
+
+  static void clearCache();
+
+ private:
+  struct ClipCacheEntry {
+    const ClipAndTransform clipAndTransform;
+    const FloatClipRect clipRect;
+    ClipCacheEntry(const ClipAndTransform& clipAndTransformArg,
+                   const FloatClipRect& clipRectArg)
+        : clipAndTransform(clipAndTransformArg), clipRect(clipRectArg) {}
+  };
+
+  void invalidateCacheIfNeeded();
+
+  Vector<ClipCacheEntry> m_clipCache;
+  unsigned m_cacheGeneration;
+
+  DISALLOW_COPY_AND_ASSIGN(GeometryMapperClipCache);
+};
+
+}  // namespace blink
+
+#endif  // GeometryMapperClipCache_h