third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.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 NGInlineBoxState_h
#define NGInlineBoxState_h

#include "core/CoreExport.h"
#include "core/layout/ng/inline/ng_line_height_metrics.h"
#include "core/style/ComputedStyleConstants.h"
#include "platform/LayoutUnit.h"
#include "platform/fonts/FontBaseline.h"
#include "platform/wtf/Vector.h"

namespace blink {

class NGInlineItem;
class NGLineBoxFragmentBuilder;
class NGTextFragmentBuilder;

// Fragments that require the layout position/size of ancestor are packed in
// this struct.
struct NGPendingPositions {
  unsigned fragment_start;
  unsigned fragment_end;
  NGLineHeightMetrics metrics;
  EVerticalAlign vertical_align;
};

// Represents the current box while NGInlineLayoutAlgorithm performs layout.
// Used 1) to cache common values for a box, and 2) to layout children that
// require ancestor position or size.
struct NGInlineBoxState {
  unsigned fragment_start;
  const ComputedStyle* style;
  NGLineHeightMetrics metrics;
  NGLineHeightMetrics text_metrics;
  LayoutUnit text_top;
  Vector<NGPendingPositions> pending_descendants;
  bool include_used_fonts = false;

  // Compute text metrics for a box. All text in a box share the same metrics.
  void ComputeTextMetrics(const ComputedStyle& style, FontBaseline);
  void AccumulateUsedFonts(const NGInlineItem&,
                           unsigned start,
                           unsigned end,
                           FontBaseline);
};

// Represents the inline tree structure. This class provides:
// 1) Allow access to fragments belonging to the current box.
// 2) Performs layout when the positin/size of a box was computed.
// 3) Cache common values for a box.
class NGInlineLayoutStateStack {
 public:
  // The box state for the line box.
  NGInlineBoxState& LineBoxState() { return stack_.front(); }

  // Initialize the box state stack for a new line.
  // @return The initial box state for the line.
  NGInlineBoxState* OnBeginPlaceItems(const ComputedStyle*, FontBaseline);

  // Push a box state stack.
  NGInlineBoxState* OnOpenTag(const NGInlineItem&,
                              NGLineBoxFragmentBuilder*,
                              NGTextFragmentBuilder*);

  // Pop a box state stack.
  NGInlineBoxState* OnCloseTag(const NGInlineItem&,
                               NGLineBoxFragmentBuilder*,
                               NGInlineBoxState*);

  // Compute all the pending positioning at the end of a line.
  void OnEndPlaceItems(NGLineBoxFragmentBuilder*);

 private:
  // End of a box state, either explicitly by close tag, or implicitly at the
  // end of a line.
  void EndBoxState(NGInlineBoxState*, NGLineBoxFragmentBuilder*);

  // Compute vertical position for the 'vertical-align' property.
  // The timing to apply varies by values; some values apply at the layout of
  // the box was computed. Other values apply when the layout of the parent or
  // the line box was computed.
  // https://www.w3.org/TR/CSS22/visudet.html#propdef-vertical-align
  // https://www.w3.org/TR/css-inline-3/#propdef-vertical-align
  void ApplyBaselineShift(NGInlineBoxState*, NGLineBoxFragmentBuilder*);

  Vector<NGInlineBoxState, 4> stack_;
};

}  // namespace blink

#endif  // NGInlineBoxState_h