third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.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 NGBlockLayoutAlgorithm_h
#define NGBlockLayoutAlgorithm_h

#include "core/CoreExport.h"
#include "core/layout/ng/geometry/ng_margin_strut.h"
#include "core/layout/ng/ng_block_break_token.h"
#include "core/layout/ng/ng_block_node.h"
#include "core/layout/ng/ng_fragment_builder.h"
#include "core/layout/ng/ng_layout_algorithm.h"
#include "platform/wtf/RefPtr.h"

namespace blink {

class NGConstraintSpace;
class NGFragment;
class NGLayoutResult;

// This struct is used for communicating to a child the position of the
// previous inflow child.
struct NGPreviousInflowPosition {
  LayoutUnit bfc_block_offset;
  LayoutUnit logical_block_offset;
  NGMarginStrut margin_strut;
  bool empty_block_affected_by_clearance;
};

// This strut holds information for the current inflow child. The data is not
// useful outside of handling this single inflow child.
struct NGInflowChildData {
  NGBfcOffset bfc_offset_estimate;
  NGMarginStrut margin_strut;
  NGBoxStrut margins;
};

// A class for general block layout (e.g. a <div> with no special style).
// Lays out the children in sequence.
class CORE_EXPORT NGBlockLayoutAlgorithm
    : public NGLayoutAlgorithm<NGBlockNode,
                               NGFragmentBuilder,
                               NGBlockBreakToken> {
 public:
  // Default constructor.
  // @param node The input node to perform layout upon.
  // @param space The constraint space which the algorithm should generate a
  //              fragment within.
  // @param break_token The break token from which the layout should start.
  NGBlockLayoutAlgorithm(NGBlockNode node,
                         const NGConstraintSpace& space,
                         NGBlockBreakToken* break_token = nullptr);

  Optional<MinMaxSize> ComputeMinMaxSize() const override;
  virtual scoped_refptr<NGLayoutResult> Layout() override;

 private:
  NGBoxStrut CalculateMargins(NGLayoutInputNode child,
                              const NGBreakToken* child_break_token);

  // Creates a new constraint space for the current child.
  scoped_refptr<NGConstraintSpace> CreateConstraintSpaceForChild(
      const NGLayoutInputNode child,
      const NGInflowChildData& child_data,
      const WTF::Optional<NGBfcOffset> floats_bfc_offset = WTF::nullopt,
      const WTF::Optional<LayoutUnit> fixed_inline_size = WTF::nullopt);

  // @return Estimated BFC offset for the "to be layout" child.
  NGInflowChildData ComputeChildData(const NGPreviousInflowPosition&,
                                     NGLayoutInputNode,
                                     const NGBreakToken* child_break_token);

  NGPreviousInflowPosition ComputeInflowPosition(
      const NGPreviousInflowPosition& previous_inflow_position,
      const NGLayoutInputNode child,
      const NGInflowChildData& child_data,
      const WTF::Optional<NGBfcOffset>& child_bfc_offset,
      const NGLogicalOffset& logical_offset,
      const NGLayoutResult& layout_result,
      const NGFragment& fragment,
      bool empty_block_affected_by_clearance);

  // Positions the fragment that knows its BFC offset.
  WTF::Optional<NGBfcOffset> PositionWithBfcOffset(
      const NGBfcOffset& bfc_offset);
  bool PositionWithBfcOffset(const NGBfcOffset& bfc_offset,
                             WTF::Optional<NGBfcOffset>* child_bfc_offset);

  // Positions using the parent BFC offset.
  // Fragment doesn't know its offset but we can still calculate its BFC
  // position because the parent fragment's BFC is known.
  // Example:
  //   BFC Offset is known here because of the padding.
  //   <div style="padding: 1px">
  //     <div id="empty-div" style="margins: 1px"></div>
  NGBfcOffset PositionWithParentBfc(const NGLayoutInputNode& child,
                                    const NGConstraintSpace&,
                                    const NGInflowChildData& child_data,
                                    const NGLayoutResult&,
                                    bool* empty_block_affected_by_clearance);

  void HandleOutOfFlowPositioned(const NGPreviousInflowPosition&, NGBlockNode);
  void HandleFloat(const NGPreviousInflowPosition&,
                   NGBlockNode,
                   NGBlockBreakToken*);

  // This uses the NGLayoutOpporunityIterator to position the fragment.
  //
  // An element that establishes a new formatting context must not overlap the
  // margin box of any floats within the current BFC.
  //
  // Example:
  // <div id="container">
  //   <div id="float"></div>
  //   <div id="new-fc" style="margin-top: 20px;"></div>
  // </div>
  // 1) If #new-fc is small enough to fit the available space right from #float
  //    then it will be placed there and we collapse its margin.
  // 2) If #new-fc is too big then we need to clear its position and place it
  //    below #float ignoring its vertical margin.
  //
  // Returns false if we need to abort layout, because a previously unknown BFC
  // offset has now been resolved.
  bool HandleNewFormattingContext(
      NGLayoutInputNode child,
      NGBreakToken* child_break_token,
      NGPreviousInflowPosition*,
      RefPtr<NGBreakToken>* previous_inline_break_token);

  // Performs the actual layout of a new formatting context. This may be called
  // multiple times from HandleNewFormattingContext.
  std::pair<scoped_refptr<NGLayoutResult>, NGLayoutOpportunity>
  LayoutNewFormattingContext(NGLayoutInputNode child,
                             NGBreakToken* child_break_token,
                             bool is_auto_inline_size,
                             const NGInflowChildData&,
                             LayoutUnit child_origin_block_offset);

  // Handle an in-flow child.
  // Returns false if we need to abort layout, because a previously unknown BFC
  // offset has now been resolved. (Same as HandleNewFormattingContext).
  bool HandleInflow(NGLayoutInputNode child,
                    NGBreakToken* child_break_token,
                    NGPreviousInflowPosition*,
                    RefPtr<NGBreakToken>* previous_inline_break_token);

  // Return the amount of block space available in the current fragmentainer
  // for the node being laid out by this algorithm.
  LayoutUnit FragmentainerSpaceAvailable() const;

  // Return true if the node being laid out by this fragmentainer has used all
  // the available space in the current fragmentainer.
  bool IsFragmentainerOutOfSpace() const;

  // Given a child fragment and the corresponding node's style, return true if
  // we need to insert a fragmentainer break in front of it.
  bool ShouldBreakBeforeChild(NGLayoutInputNode child,
                              const NGPhysicalFragment& physical_fragment,
                              LayoutUnit block_offset) const;

  // Final adjustments before fragment creation. We need to prevent the
  // fragment from crossing fragmentainer boundaries, and rather create a break
  // token if we're out of space.
  void FinalizeForFragmentation();

  void PropagateBaselinesFromChildren();
  bool AddBaseline(const NGBaselineRequest&,
                   const NGPhysicalFragment*,
                   LayoutUnit child_offset);

  // Updates the fragment's BFC offset if it's not already set.
  bool MaybeUpdateFragmentBfcOffset(LayoutUnit bfc_block_offset);

  // Positions pending floats starting from {@origin_block_offset}.
  void PositionPendingFloats(LayoutUnit origin_block_offset);

  // Adds a set of positioned floats as children to the current fragment.
  void AddPositionedFloats(const Vector<NGPositionedFloat>& positioned_floats);

  // Calculates logical offset for the current fragment using either {@code
  // intrinsic_block_size_} when the fragment doesn't know it's offset or
  // {@code known_fragment_offset} if the fragment knows it's offset
  // @return Fragment's offset relative to the fragment's parent.
  NGLogicalOffset CalculateLogicalOffset(
      const NGFragment&,
      const NGBoxStrut& child_margins,
      const WTF::Optional<NGBfcOffset>& known_fragment_offset);

  NGLogicalSize child_available_size_;
  NGLogicalSize child_percentage_size_;

  NGBoxStrut border_scrollbar_padding_;
  LayoutUnit intrinsic_block_size_;

  bool abort_when_bfc_resolved_;

  std::unique_ptr<NGExclusionSpace> exclusion_space_;
  Vector<scoped_refptr<NGUnpositionedFloat>> unpositioned_floats_;
};

}  // namespace blink

#endif  // NGBlockLayoutAlgorithm_h