Replace collectLayerFragments() with FragmentainerIterator.

third_party/WebKit/Source/core/layout/FragmentainerIterator.h

+// Copyright 2016 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 FragmentainerIterator_h
+#define FragmentainerIterator_h
+
+#include "core/layout/LayoutFlowThread.h"
+
+namespace blink {
+
+class MultiColumnFragmentainerGroup;
+
+// Used to find the fragmentainers that intersect with a given portion of the flow thread. The
+// portion typically corresponds to the bounds of some descendant layout object. The iterator walks
+// in block direction order.
+class FragmentainerIterator {
+public:
+    FragmentainerIterator(const LayoutFlowThread&, const LayoutRect& physicalBoundingBoxInFlowThread, const LayoutRect& clipRectInMulticolContainer);
+
+    // Advance to the next fragmentainer. Not allowed to call this if atEnd() is true.
+    void advance();
+
+    // Return true if we have walked through all relevant fragmentainers.
+    bool atEnd() const { return !m_currentColumnSet; }
+
+    // The physical translation to apply to shift the box when converting from flowthread to visual
+    // coordinates.
+    LayoutSize paginationOffset() const { DCHECK(!atEnd()); return m_paginationOffset; }
+
+    // Return the physical clip rectangle of the current fragmentainer, relative to the flow thread.
+    LayoutRect clipRectInFlowThread() const { DCHECK(!atEnd()); return m_clipRectInFlowThread; }
+
+private:
+    const LayoutFlowThread& m_flowThread;
+    const LayoutRect m_clipRectInMulticolContainer;
+
+    const LayoutMultiColumnSet* m_currentColumnSet;
+    unsigned m_currentFragmentainerGroupIndex;
+    unsigned m_currentFragmentainerIndex;
+    unsigned m_endFragmentainerIndex;
+
+    LayoutUnit m_logicalTopInFlowThread;
+    LayoutUnit m_logicalBottomInFlowThread;
+
+    LayoutSize m_paginationOffset;
+    LayoutRect m_clipRectInFlowThread;
+
+    const MultiColumnFragmentainerGroup& currentGroup() const;
+    void moveToNextFragmentainerGroup();
+    bool setFragmentainersOfInterest();
+    void updateOutput();
+    void setAtEnd() { m_currentColumnSet = nullptr; }
+};
+
+} // namespace blink
+
+#endif // FragmentainerIterator_h
+