third_party/blink/renderer/core/layout/ng/ng_constraint_space.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 NGConstraintSpace_h
#define NGConstraintSpace_h

#include "base/optional.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/layout/ng/exclusions/ng_exclusion_space.h"
#include "third_party/blink/renderer/core/layout/ng/geometry/ng_bfc_offset.h"
#include "third_party/blink/renderer/core/layout/ng/geometry/ng_logical_size.h"
#include "third_party/blink/renderer/core/layout/ng/geometry/ng_margin_strut.h"
#include "third_party/blink/renderer/core/layout/ng/geometry/ng_physical_size.h"
#include "third_party/blink/renderer/core/layout/ng/inline/ng_baseline.h"
#include "third_party/blink/renderer/core/layout/ng/ng_floats_utils.h"
#include "third_party/blink/renderer/platform/text/text_direction.h"
#include "third_party/blink/renderer/platform/text/writing_mode.h"
#include "third_party/blink/renderer/platform/wtf/ref_counted.h"
#include "third_party/blink/renderer/platform/wtf/text/wtf_string.h"

namespace blink {

class LayoutBox;
class NGConstraintSpaceBuilder;

enum NGFragmentationType {
  kFragmentNone,
  kFragmentPage,
  kFragmentColumn,
  kFragmentRegion
};

// Tables have two passes, a "measure" phase (for determining the table row
// height), and a "layout" phase.
// See: https://drafts.csswg.org/css-tables-3/#row-layout
//
// This enum is used for communicating to *direct* children of table cells,
// which layout phase the table cell is in.
enum NGTableCellChildLayoutPhase {
  kNotTableCellChild,  // The node isn't a table cell child.
  kMeasure,  // The node is a table cell child, in the "measure" phase.
  kLayout    // The node is a table cell child, in the "layout" phase.
};

// The NGConstraintSpace represents a set of constraints and available space
// which a layout algorithm may produce a NGFragment within.
class CORE_EXPORT NGConstraintSpace final {
  USING_FAST_MALLOC(NGConstraintSpace);

 public:
  enum ConstraintSpaceFlags {
    kOrthogonalWritingModeRoot = 1 << 0,
    kFixedSizeInline = 1 << 1,
    kFixedSizeBlock = 1 << 2,
    kFixedSizeBlockIsDefinite = 1 << 3,
    kShrinkToFit = 1 << 4,
    kIntermediateLayout = 1 << 5,
    kSeparateLeadingFragmentainerMargins = 1 << 6,
    kNewFormattingContext = 1 << 7,
    kAnonymous = 1 << 8,
    kUseFirstLineStyle = 1 << 9,
    kForceClearance = 1 << 10,

    // Size of bitfield used to store the flags.
    kNumberOfConstraintSpaceFlags = 11
  };

  NGConstraintSpace() {}
  NGConstraintSpace(const NGConstraintSpace&) = default;
  NGConstraintSpace(NGConstraintSpace&&) = default;
  NGConstraintSpace& operator=(const NGConstraintSpace&) = default;
  NGConstraintSpace& operator=(NGConstraintSpace&&) = default;

  // Creates NGConstraintSpace representing LayoutObject's containing block.
  // This should live on NGBlockNode or another layout bridge and probably take
  // a root NGConstraintSpace.
  static NGConstraintSpace CreateFromLayoutObject(const LayoutBox&);

  const NGExclusionSpace& ExclusionSpace() const { return exclusion_space_; }

  TextDirection Direction() const {
    return static_cast<TextDirection>(direction_);
  }

  WritingMode GetWritingMode() const {
    return static_cast<WritingMode>(writing_mode_);
  }

  bool IsOrthogonalWritingModeRoot() const {
    return HasFlag(kOrthogonalWritingModeRoot);
  }

  // The size to use for percentage resolution.
  // See: https://drafts.csswg.org/css-sizing/#percentage-sizing
  NGLogicalSize PercentageResolutionSize() const {
    return percentage_resolution_size_;
  }

  // The size to use for percentage resolution of replaced elements.
  NGLogicalSize ReplacedPercentageResolutionSize() const {
    return replaced_percentage_resolution_size_;
  }

  // The size to use for percentage resolution for margin/border/padding.
  // They are always get computed relative to the inline size, in the parent
  // writing mode.
  LayoutUnit PercentageResolutionInlineSizeForParentWritingMode() const {
    if (!IsOrthogonalWritingModeRoot())
      return PercentageResolutionSize().inline_size;
    if (PercentageResolutionSize().block_size != NGSizeIndefinite)
      return PercentageResolutionSize().block_size;
    // TODO(mstensho): Figure out why we get here. It seems wrong, but we do get
    // here in some grid layout situations.
    return LayoutUnit();
  }

  // The available space size.
  // See: https://drafts.csswg.org/css-sizing/#available
  NGLogicalSize AvailableSize() const { return available_size_; }

  NGPhysicalSize InitialContainingBlockSize() const {
    return initial_containing_block_size_;
  }

  LayoutUnit FragmentainerBlockSize() const {
    return fragmentainer_block_size_;
  }

  // Return the block space that was available in the current fragmentainer at
  // the start of the current block formatting context. Note that if the start
  // of the current block formatting context is in a previous fragmentainer, the
  // size of the current fragmentainer is returned instead.
  LayoutUnit FragmentainerSpaceAtBfcStart() const {
    DCHECK(HasBlockFragmentation());
    return fragmentainer_space_at_bfc_start_;
  }

  // Whether the current constraint space is for the newly established
  // Formatting Context.
  bool IsNewFormattingContext() const { return HasFlag(kNewFormattingContext); }

  // Return true if we are to separate (i.e. honor, rather than collapse)
  // block-start margins at the beginning of fragmentainers. This only makes a
  // difference if we're block-fragmented (pagination, multicol, etc.). Then
  // block-start margins at the beginning of a fragmentainers are to be
  // truncated to 0 if they occur after a soft (unforced) break.
  bool HasSeparateLeadingFragmentainerMargins() const {
    return HasFlag(kSeparateLeadingFragmentainerMargins);
  }

  // Whether the fragment produced from layout should be anonymous, (e.g. it
  // may be a column in a multi-column layout). In such cases it shouldn't have
  // any borders or padding.
  bool IsAnonymous() const { return HasFlag(kAnonymous); }

  // Whether to use the ':first-line' style or not.
  // Note, this is not about the first line of the content to layout, but
  // whether the constraint space itself is on the first line, such as when it's
  // an inline block.
  // Also note this is true only when the document has ':first-line' rules.
  bool UseFirstLineStyle() const { return HasFlag(kUseFirstLineStyle); }

  // Some layout modes “stretch” their children to a fixed size (e.g. flex,
  // grid). These flags represented whether a layout needs to produce a
  // fragment that satisfies a fixed constraint in the inline and block
  // direction respectively.
  //
  // If these flags are true, the AvailableSize() is interpreted as the fixed
  // border-box size of this box in the respective dimension.
  bool IsFixedSizeInline() const { return HasFlag(kFixedSizeInline); }

  bool IsFixedSizeBlock() const { return HasFlag(kFixedSizeBlock); }

  // Whether a fixed block size should be considered definite.
  bool FixedSizeBlockIsDefinite() const {
    return HasFlag(kFixedSizeBlockIsDefinite);
  }

  // Whether an auto inline-size should be interpreted as shrink-to-fit
  // (ie. fit-content). This is used for inline-block, floats, etc.
  bool IsShrinkToFit() const { return HasFlag(kShrinkToFit); }

  // Whether this constraint space is used for an intermediate layout in a
  // multi-pass layout. In such a case, we should not copy back the resulting
  // layout data to the legacy tree or create a paint fragment from it.
  bool IsIntermediateLayout() const { return HasFlag(kIntermediateLayout); }

  // If specified a layout should produce a Fragment which fragments at the
  // blockSize if possible.
  NGFragmentationType BlockFragmentationType() const {
    return static_cast<NGFragmentationType>(
        block_direction_fragmentation_type_);
  }

  // Return true if this constraint space participates in a fragmentation
  // context.
  bool HasBlockFragmentation() const {
    return BlockFragmentationType() != kFragmentNone;
  }

  // Returns if this node is a table cell child, and which table layout phase
  // is occurring.
  NGTableCellChildLayoutPhase TableCellChildLayoutPhase() const {
    return static_cast<NGTableCellChildLayoutPhase>(
        table_cell_child_layout_phase_);
  }

  NGMarginStrut MarginStrut() const { return margin_strut_; }

  // The BfcOffset is where the MarginStrut is placed within the block
  // formatting context.
  //
  // The current layout or a descendant layout may "resolve" the BFC offset,
  // i.e. decide where the current fragment should be placed within the BFC.
  //
  // This is done by:
  //   bfc_block_offset =
  //     space.BfcOffset().block_offset + space.MarginStrut().Sum();
  //
  // The BFC offset can get "resolved" in many circumstances (including, but
  // not limited to):
  //   - block_start border or padding in the current layout.
  //   - Text content, atomic inlines, (see NGLineBreaker).
  //   - The current layout having a block_size.
  //   - Clearance before a child.
  NGBfcOffset BfcOffset() const { return bfc_offset_; }

  // If present, and the current layout hasn't resolved its BFC offset yet (see
  // BfcOffset), the layout should position all of its unpositioned floats at
  // this offset. This value is the BFC offset that we calculated in the
  // previous pass, a pass which aborted once the BFC offset got resolved,
  // because we had walked past content (i.e. floats) that depended on it being
  // resolved.
  //
  // This value should be propogated to child layouts if the current layout
  // hasn't resolved its BFC offset yet.
  //
  // This value is calculated *after* an initial pass of the tree, and should
  // only be present during subsequent passes.
  base::Optional<LayoutUnit> FloatsBfcBlockOffset() const {
    return floats_bfc_block_offset_;
  }

  // Return the types (none, left, right, both) of preceding adjoining
  // floats. These are floats that are added while the in-flow BFC offset is
  // still unknown. The floats may or may not be unpositioned (pending). That
  // depends on which layout pass we're in. They are typically positioned if
  // FloatsBfcOffset() is known. Adjoining floats should be treated differently
  // when calculating clearance on a block with adjoining block-start margin.
  // (in such cases we will know up front that the block will need clearance,
  // since, if it doesn't, the float will be pulled along with the block, and
  // the block will fail to clear).
  NGFloatTypes AdjoiningFloatTypes() const { return adjoining_floats_; }

  bool HasClearanceOffset() const {
    return clearance_offset_ != LayoutUnit::Min();
  }
  LayoutUnit ClearanceOffset() const { return clearance_offset_; }

  // Return true if the fragment needs to have clearance applied to it,
  // regardless of its hypothetical position. The fragment will then go exactly
  // below the relevant floats. This happens when a cleared child gets separated
  // from floats that would otherwise be adjoining; example:
  //
  // <div id="container">
  //   <div id="float" style="float:left; width:100px; height:100px;"></div>
  //   <div id="clearee" style="clear:left; margin-top:12345px;">text</div>
  // </div>
  //
  // Clearance separates #clearee from #container, and #float is positioned at
  // the block-start content edge of #container. Without clearance, margins
  // would have been adjoining and the large margin on #clearee would have
  // pulled both #container and #float along with it. No margin, no matter how
  // large, would ever be able to pull #clearee below the float then. But we
  // have clearance, the margins are separated, and in this case we know that we
  // have clearance even before we have laid out (because of the adjoing
  // float). So it would just be wrong to check for clearance when we position
  // #clearee. Nothing can prevent clearance here. A large margin on the cleared
  // child will be canceled out with negative clearance.
  bool ShouldForceClearance() const { return HasFlag(kForceClearance); }

  const NGBaselineRequestList BaselineRequests() const {
    return NGBaselineRequestList(baseline_requests_);
  }

  bool operator==(const NGConstraintSpace&) const;
  bool operator!=(const NGConstraintSpace& other) const {
    return !(*this == other);
  }

  String ToString() const;

 private:
  friend class NGConstraintSpaceBuilder;
  // Default constructor.
  // is_new_fc is technically redundant, but simplifies the code here a bit.
  NGConstraintSpace(WritingMode out_writing_mode,
                    bool is_new_fc,
                    NGConstraintSpaceBuilder& builder);

  bool HasFlag(ConstraintSpaceFlags mask) const {
    return flags_ & static_cast<unsigned>(mask);
  }

  NGLogicalSize available_size_;
  NGLogicalSize percentage_resolution_size_;
  NGLogicalSize replaced_percentage_resolution_size_;
  NGPhysicalSize initial_containing_block_size_;

  NGMarginStrut margin_strut_;
  NGBfcOffset bfc_offset_;
  base::Optional<LayoutUnit> floats_bfc_block_offset_;

  NGExclusionSpace exclusion_space_;

  LayoutUnit fragmentainer_block_size_;
  LayoutUnit fragmentainer_space_at_bfc_start_;

  LayoutUnit clearance_offset_;

  unsigned block_direction_fragmentation_type_ : 2;
  unsigned table_cell_child_layout_phase_ : 2;  // NGTableCellChildLayoutPhase
  unsigned adjoining_floats_ : 2;               // NGFloatTypes
  unsigned writing_mode_ : 3;
  unsigned direction_ : 1;
  unsigned flags_ : kNumberOfConstraintSpaceFlags;  // ConstraintSpaceFlags
  unsigned baseline_requests_ : NGBaselineRequestList::kSerializedBits;
};

inline std::ostream& operator<<(std::ostream& stream,
                                const NGConstraintSpace& value) {
  return stream << value.ToString();
}

}  // namespace blink

#endif  // NGConstraintSpace_h