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// 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 LayoutBlock;
class NGConstraintSpaceBuilder;
enum NGFragmentationType {
// Tables have two passes, a "measure" phase (for determining the table row
// height), and a "layout" phase.
// See:
// This enum is used for communicating to *direct* children of table cells,
// which layout phase the table cell is in.
enum class 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.
// Percentages are frequently the same as the available-size, zero, or
// indefinite (thanks non-quirks mode)! This enum encodes this information.
enum NGPercentageStorage {
// The NGConstraintSpace represents a set of constraints and available space
// which a layout algorithm may produce a NGFragment within.
class CORE_EXPORT NGConstraintSpace final {
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,
kHasRareData = 1 << 11,
// Size of bitfield used to store the flags.
kNumberOfConstraintSpaceFlags = 12
// To ensure that the bfc_offset_, rare_data_ union doesn't get polluted,
// always initialize the bfc_offset_.
NGConstraintSpace() : bfc_offset_() {}
NGConstraintSpace(const NGConstraintSpace& other)
: available_size_(other.available_size_),
bitfields_(other.bitfields_) {
if (HasRareData())
rare_data_ = new RareData(*other.rare_data_);
bfc_offset_ = other.bfc_offset_;
NGConstraintSpace(NGConstraintSpace&& other)
: available_size_(other.available_size_),
bitfields_(other.bitfields_) {
if (HasRareData()) {
rare_data_ = other.rare_data_;
other.rare_data_ = nullptr;
} else {
bfc_offset_ = other.bfc_offset_;
NGConstraintSpace& operator=(const NGConstraintSpace& other) {
available_size_ = other.available_size_;
if (HasRareData())
delete rare_data_;
if (other.HasRareData())
rare_data_ = new RareData(*other.rare_data_);
bfc_offset_ = other.bfc_offset_;
exclusion_space_ = other.exclusion_space_;
bitfields_ = other.bitfields_;
return *this;
NGConstraintSpace& operator=(NGConstraintSpace&& other) {
available_size_ = other.available_size_;
if (HasRareData())
delete rare_data_;
if (other.HasRareData()) {
rare_data_ = other.rare_data_;
other.rare_data_ = nullptr;
} else {
bfc_offset_ = other.bfc_offset_;
exclusion_space_ = std::move(other.exclusion_space_);
bitfields_ = other.bitfields_;
return *this;
~NGConstraintSpace() {
if (HasRareData())
delete rare_data_;
// 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 LayoutBlock&);
const NGExclusionSpace& ExclusionSpace() const { return exclusion_space_; }
TextDirection Direction() const {
return static_cast<TextDirection>(bitfields_.direction);
WritingMode GetWritingMode() const {
return static_cast<WritingMode>(bitfields_.writing_mode);
bool IsOrthogonalWritingModeRoot() const {
return HasFlag(kOrthogonalWritingModeRoot);
// The available space size.
// See:
NGLogicalSize AvailableSize() const { return available_size_; }
// The size to use for percentage resolution.
// See:
LayoutUnit PercentageResolutionInlineSize() const {
switch (static_cast<NGPercentageStorage>(
bitfields_.percentage_inline_storage)) {
case kSameAsAvailable:
return available_size_.inline_size;
case kZero:
return LayoutUnit();
case kIndefinite:
return NGSizeIndefinite;
case kRareDataPercentage:
return rare_data_->percentage_resolution_size.inline_size;
LayoutUnit PercentageResolutionBlockSize() const {
switch (
static_cast<NGPercentageStorage>(bitfields_.percentage_block_storage)) {
case kSameAsAvailable:
return available_size_.block_size;
case kZero:
return LayoutUnit();
case kIndefinite:
return NGSizeIndefinite;
case kRareDataPercentage:
return rare_data_->percentage_resolution_size.block_size;
NGLogicalSize PercentageResolutionSize() const {
return {PercentageResolutionInlineSize(), PercentageResolutionBlockSize()};
LayoutUnit ReplacedPercentageResolutionInlineSize() const {
return PercentageResolutionInlineSize();
LayoutUnit ReplacedPercentageResolutionBlockSize() const {
switch (static_cast<NGPercentageStorage>(
bitfields_.replaced_percentage_block_storage)) {
case kSameAsAvailable:
return available_size_.block_size;
case kZero:
return LayoutUnit();
case kIndefinite:
return NGSizeIndefinite;
case kRareDataPercentage:
return rare_data_->replaced_percentage_resolution_block_size;
return available_size_.block_size;
// The size to use for percentage resolution of replaced elements.
NGLogicalSize ReplacedPercentageResolutionSize() const {
return {ReplacedPercentageResolutionInlineSize(),
// 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 PercentageResolutionInlineSize();
if (PercentageResolutionBlockSize() != NGSizeIndefinite)
return PercentageResolutionBlockSize();
// TODO(mstensho): Figure out why we get here. It seems wrong, but we do get
// here in some grid layout situations.
return LayoutUnit();
LayoutUnit FragmentainerBlockSize() const {
return HasRareData() ? rare_data_->fragmentainer_block_size
: NGSizeIndefinite;
// 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 {
return HasRareData() ? rare_data_->fragmentainer_space_at_bfc_start
: NGSizeIndefinite;
// 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 HasRareData() ? static_cast<NGFragmentationType>(
: kFragmentNone;
// 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>(
NGMarginStrut MarginStrut() const {
return HasRareData() ? rare_data_->margin_strut : NGMarginStrut();
// 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 HasRareData() ? rare_data_->bfc_offset : 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 HasRareData() ? rare_data_->floats_bfc_block_offset : base::nullopt;
// 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 bitfields_.adjoining_floats;
// Return true if there were any earlier floats that may affect the current
// layout.
bool HasFloats() const { return !ExclusionSpace().IsEmpty(); }
bool HasClearanceOffset() const {
return HasRareData() && rare_data_->clearance_offset != LayoutUnit::Min();
LayoutUnit ClearanceOffset() const {
return HasRareData() ? rare_data_->clearance_offset : LayoutUnit::Min();
// 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 adjoining
// 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(bitfields_.baseline_requests);
// Return true if the two constraint spaces are similar enough that it *may*
// be possible to skip re-layout. If true is returned, the caller is expected
// to verify that any constraint space size (available size, percentage size,
// and so on) and BFC offset changes won't require re-layout, before skipping.
bool MaySkipLayout(const NGConstraintSpace& other) const {
if (HasRareData() && other.HasRareData()) {
if (!rare_data_->MaySkipLayout(*other.rare_data_))
return false;
} else if (!HasRareData() && !other.HasRareData()) {
if (bfc_offset_.line_offset != other.bfc_offset_.line_offset)
return false;
} else {
// We have a bfc_offset_, and a rare_data_ (or vice-versa).
return false;
return exclusion_space_ == other.exclusion_space_ &&
bool AreSizesEqual(const NGConstraintSpace& other) const {
if (available_size_ != other.available_size_)
return false;
if (bitfields_.percentage_inline_storage !=
return false;
if (bitfields_.percentage_block_storage !=
return false;
if (bitfields_.replaced_percentage_inline_storage !=
return false;
if (bitfields_.replaced_percentage_block_storage !=
return false;
// The rest of this method just checks the percentage resolution sizes. If
// neither space has rare data, we know that they must equal now.
if (!HasRareData() && !other.HasRareData())
return true;
if (bitfields_.percentage_inline_storage == kRareDataPercentage &&
other.bitfields_.percentage_inline_storage == kRareDataPercentage &&
rare_data_->percentage_resolution_size.inline_size !=
return false;
if (bitfields_.percentage_block_storage == kRareDataPercentage &&
other.bitfields_.percentage_block_storage == kRareDataPercentage &&
rare_data_->percentage_resolution_size.block_size !=
return false;
if (bitfields_.replaced_percentage_block_storage == kRareDataPercentage &&
other.bitfields_.replaced_percentage_block_storage ==
kRareDataPercentage &&
rare_data_->replaced_percentage_resolution_block_size !=
return false;
return true;
bool operator==(const NGConstraintSpace&) const;
bool operator!=(const NGConstraintSpace& other) const {
return !(*this == other);
String ToString() const;
friend class NGConstraintSpaceBuilder;
explicit NGConstraintSpace(WritingMode writing_mode)
: bfc_offset_(), bitfields_(writing_mode) {}
// This struct defines all of the inputs to layout which we consider rare.
// Primarily this is:
// - Percentage resolution sizes which differ from the available size or
// aren't indefinite.
// - The margin strut.
// - Anything to do with floats (the exclusion space, clearance offset, etc).
// - Anything to do with fragmentation.
// This information is kept in a separate in this heap-allocated struct to
// reduce memory usage. Over time this may have to change based on usage data.
struct RareData {
explicit RareData(const NGBfcOffset bfc_offset)
: bfc_offset(bfc_offset),
static_cast<unsigned>(kFragmentNone)) {}
RareData(const RareData&) = default;
~RareData() = default;
NGLogicalSize percentage_resolution_size;
LayoutUnit replaced_percentage_resolution_block_size;
NGBfcOffset bfc_offset;
NGMarginStrut margin_strut;
base::Optional<LayoutUnit> floats_bfc_block_offset;
LayoutUnit clearance_offset = LayoutUnit::Min();
LayoutUnit fragmentainer_block_size = NGSizeIndefinite;
LayoutUnit fragmentainer_space_at_bfc_start = NGSizeIndefinite;
unsigned block_direction_fragmentation_type : 2;
bool MaySkipLayout(const RareData& other) const {
return margin_strut == other.margin_strut &&
bfc_offset.line_offset == other.bfc_offset.line_offset &&
floats_bfc_block_offset == other.floats_bfc_block_offset &&
clearance_offset == other.clearance_offset &&
fragmentainer_block_size == other.fragmentainer_block_size &&
fragmentainer_space_at_bfc_start ==
other.fragmentainer_space_at_bfc_start &&
block_direction_fragmentation_type ==
// This struct simply allows us easily copy, compare, and initialize all the
// bitfields without having to explicitly copy, compare, and initialize each
// one (see the outer class constructors, and assignment operators).
struct Bitfields {
// We explicitly define a default constructor to ensure the kHasRareData
// bitfield doesn't accidently get set.
Bitfields() : Bitfields(WritingMode::kHorizontalTb) {}
explicit Bitfields(WritingMode writing_mode)
: table_cell_child_layout_phase(static_cast<unsigned>(
replaced_percentage_block_storage(kSameAsAvailable) {}
bool MaySkipLayout(const Bitfields& other) const {
return table_cell_child_layout_phase ==
other.table_cell_child_layout_phase &&
adjoining_floats == other.adjoining_floats &&
writing_mode == other.writing_mode && flags == other.flags &&
baseline_requests == other.baseline_requests;
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;
unsigned percentage_inline_storage : 2; // NGPercentageStorage
unsigned percentage_block_storage : 2; // NGPercentageStorage
unsigned replaced_percentage_inline_storage : 2; // NGPercentageStorage
unsigned replaced_percentage_block_storage : 2; // NGPercentageStorage
inline bool HasFlag(ConstraintSpaceFlags mask) const {
return bitfields_.flags & static_cast<unsigned>(mask);
inline bool HasRareData() const { return HasFlag(kHasRareData); }
RareData* EnsureRareData() {
if (!HasRareData()) {
rare_data_ = new RareData(bfc_offset_);
bitfields_.flags |= kHasRareData;
return rare_data_;
NGLogicalSize available_size_;
// To save a little space, we union these two fields. rare_data_ is valid if
// the kHasRareData bitfield is set, otherwise bfc_offset_ is valid.
union {
NGBfcOffset bfc_offset_;
RareData* rare_data_;
NGExclusionSpace exclusion_space_;
Bitfields bitfields_;
inline std::ostream& operator<<(std::ostream& stream,
const NGConstraintSpace& value) {
return stream << value.ToString();
} // namespace blink
#endif // NGConstraintSpace_h