Canvas2d: Make the intersection computation O(1) instead of O(n) in ClipList.

third_party/WebKit/Source/modules/canvas2d/ClipList.cpp

 // Copyright 2014 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.
 
 #include "modules/canvas2d/ClipList.h"
 
 #include "platform/transforms/AffineTransform.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/pathops/SkPathOps.h"
 
 namespace blink {
 
 ClipList::ClipList(const ClipList& other) : m_clipList(other.m_clipList) { }
 
 void ClipList::clipPath(const SkPath& path, AntiAliasingMode antiAliasingMode, const SkMatrix& ctm)
 {
     ClipOp newClip;
     newClip.m_antiAliasingMode = antiAliasingMode;
     newClip.m_path = path;
     newClip.m_path.transform(ctm);
+    if (m_clipList.isEmpty())
+        m_currentClipPath = path;
+    else
+        Op(m_currentClipPath, path, SkPathOp::kIntersect_SkPathOp, &m_currentClipPath);
     m_clipList.append(newClip);
 }
 
 void ClipList::playback(SkCanvas* canvas) const
 {
     for (const ClipOp* it = m_clipList.begin(); it < m_clipList.end(); it++) {
         canvas->clipPath(it->m_path, SkRegion::kIntersect_Op, it->m_antiAliasingMode == AntiAliased);
     }
 }
 
-SkPath ClipList::intersectPathWithClip(const SkPath& path) const
+const SkPath& ClipList::getCurrentClipPath() const
 {
-    SkPath total = path;
-    for (const ClipOp* it = m_clipList.begin(); it < m_clipList.end(); it++) {
-        Op(total, it->m_path, SkPathOp::kIntersect_SkPathOp, &total);
-    }
-    return total;
+    return m_currentClipPath;
 }
 
 ClipList::ClipOp::ClipOp()
     : m_antiAliasingMode(AntiAliased)
 { }
 
 ClipList::ClipOp::ClipOp(const ClipOp& other)
     : m_path(other.m_path)
     , m_antiAliasingMode(other.m_antiAliasingMode)
 { }
 
 } // namespace blink