third_party/WebKit/Source/core/layout/line/TrailingObjects.h

/*
 * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
 * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc.
 *               All right reserved.
 * Copyright (C) 2010 Google Inc. All rights reserved.
 * Copyright (C) 2014 Adobe Systems Inc.
 *
 * 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
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef TrailingObjects_h
#define TrailingObjects_h

#include "core/layout/api/LineLayoutItem.h"
#include "core/layout/api/LineLayoutText.h"
#include "wtf/Allocator.h"
#include "wtf/Vector.h"

namespace blink {

class InlineIterator;

struct BidiRun;
struct BidiIsolatedRun;

template <class Iterator, class Run, class IsolatedRun>
class BidiResolver;
template <class Iterator>
class MidpointState;
typedef BidiResolver<InlineIterator, BidiRun, BidiIsolatedRun>
    InlineBidiResolver;
typedef MidpointState<InlineIterator> LineMidpointState;

// This class allows us to ensure lineboxes are created in the right place on
// the line when an out-of-flow positioned object or an empty inline is
// encountered between a trailing space and subsequent spaces and we want to
// ignore (i.e. collapse) surplus whitespace. So for example:
//   <div>X <span></span> Y</div>
// or
//   <div>X <div style="position: absolute"></div> Y</div>
// In both of the above snippets the inline and the positioned object occur
// after a trailing space and before a space that will cause our line breaking
// algorithm to start ignoring spaces. When it does that we want to ensure that
// the inline/positioned object gets a linebox and that it is part of the
// collapsed whitespace. So to achieve this we use appendObjectIfNeeded() to
// keep track of objects encountered after a trailing whitespace and
// updateMidpointsForTrailingObjects() to put them in the right place when we
// start ignoring surplus whitespace.

class TrailingObjects {
  STACK_ALLOCATED();

 public:
  TrailingObjects() : m_whitespace(nullptr) {}

  void setTrailingWhitespace(LineLayoutText whitespace) {
    ASSERT(whitespace);
    m_whitespace = whitespace;
  }

  void clear() {
    m_whitespace = LineLayoutText();
    // Using resize(0) rather than clear() here saves 2% on
    // PerformanceTests/Layout/line-layout.html because we avoid freeing and
    // re-allocating the underlying buffer repeatedly.
    m_objects.resize(0);
  }

  void appendObjectIfNeeded(LineLayoutItem object) {
    if (m_whitespace)
      m_objects.append(object);
  }

  enum CollapseFirstSpaceOrNot { DoNotCollapseFirstSpace, CollapseFirstSpace };

  void updateMidpointsForTrailingObjects(LineMidpointState&,
                                         const InlineIterator& lBreak,
                                         CollapseFirstSpaceOrNot);

 private:
  LineLayoutText m_whitespace;
  Vector<LineLayoutItem, 4> m_objects;
};

}  // namespace blink

#endif  // TrailingObjects_h