Top down version of algorithm to position margins and floats in LayoutNG

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc

Index: third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
index bd107013392b4316412488ea3648a0372bcb5893..dc1b8e35dc7f303cd0af59062a5597f1be610743 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
@@ -23,24 +23,32 @@
 namespace blink {
 namespace {
 
-// Adjusts content's offset to CSS "clear" property.
-// TODO(glebl): Support margin collapsing edge cases, e.g. margin collapsing
-// should not occur if "clear" is applied to non-floating blocks.
-// TODO(layout-ng): the call to AdjustToClearance should be moved to
-// CreateConstraintSpaceForChild once ConstraintSpaceBuilder is sharing the
-// exclusion information between constraint spaces.
-void AdjustToClearance(const NGConstraintSpace& space,
+// Adjusts content_size to CSS "clear" property.
+// Picks up the maximum between left/right exclusions and content_size depending
+// on the value of style.clear() property.
+void AdjustToClearance(const std::shared_ptr<NGExclusions>& exclusions,
                        const ComputedStyle& style,
+                       const NGLogicalOffset& from_offset,
                        LayoutUnit* content_size) {
-  const NGExclusion* right_exclusion = space.Exclusions()->last_right_float;
-  const NGExclusion* left_exclusion = space.Exclusions()->last_left_float;
-
-  // Calculates Left/Right block end offset from left/right float exclusions or
-  // use the default content offset position.
-  LayoutUnit left_block_end_offset =
-      left_exclusion ? left_exclusion->rect.BlockEndOffset() : *content_size;
-  LayoutUnit right_block_end_offset =
-      right_exclusion ? right_exclusion->rect.BlockEndOffset() : *content_size;
+  DCHECK(content_size) << "content_size cannot be null here";
+  const NGExclusion* right_exclusion = exclusions->last_right_float;
+  const NGExclusion* left_exclusion = exclusions->last_left_float;
+
+  // Exclusions(stored in BFC coordinates), content_size can be negative or 0
+  // If left or right exclusion are available then convert them to the relative
+  // offset(exclusion.BlockEnd - from_offset) and compare them with content_size
+  LayoutUnit left_block_end_offset = *content_size;
+  if (left_exclusion) {
+    left_block_end_offset = std::max(
+        left_exclusion->rect.BlockEndOffset() - from_offset.block_offset,
+        *content_size);
+  }
+  LayoutUnit right_block_end_offset = *content_size;
+  if (right_exclusion) {
+    right_block_end_offset = std::max(
+        right_exclusion->rect.BlockEndOffset() - from_offset.block_offset,
+        *content_size);
+  }
 
   switch (style.clear()) {
     case EClear::ClearNone:
@@ -59,21 +67,12 @@ void AdjustToClearance(const NGConstraintSpace& space,
   }
 }
 
-LayoutUnit ComputeCollapsedMarginBlockStart(
-    const NGDeprecatedMarginStrut& prev_margin_strut,
-    const NGDeprecatedMarginStrut& curr_margin_strut) {
-  return std::max(prev_margin_strut.margin_block_end,
-                  curr_margin_strut.margin_block_start) -
-         std::max(prev_margin_strut.negative_margin_block_end.abs(),
-                  curr_margin_strut.negative_margin_block_start.abs());
-}
-
 // Creates an exclusion from the fragment that will be placed in the provided
 // layout opportunity.
 NGExclusion CreateExclusion(const NGFragment& fragment,
                             const NGLayoutOpportunity& opportunity,
-                            LayoutUnit float_offset,
-                            NGBoxStrut margins,
+                            const LayoutUnit& float_offset,

[ikilpatrick, 2017/01/26 04:37:25]

drop reference.

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+                            const NGBoxStrut& margins,
                             NGExclusion::Type exclusion_type) {
   NGExclusion exclusion;
   exclusion.type = exclusion_type;
@@ -81,16 +80,30 @@ NGExclusion CreateExclusion(const NGFragment& fragment,
   rect.offset = opportunity.offset;
   rect.offset.inline_offset += float_offset;
 
-  rect.size.inline_size = fragment.InlineSize();
-  rect.size.block_size = fragment.BlockSize();
-
-  // Adjust to child's margin.
-  rect.size.block_size += margins.BlockSum();
-  rect.size.inline_size += margins.InlineSum();
-
+  rect.size.inline_size = fragment.InlineSize() + margins.InlineSum();
+  rect.size.block_size = fragment.BlockSize() + margins.BlockSum();
   return exclusion;
 }
 
+// Adjusts the provided offset to the top edge alignment rule.
+// Top edge alignment rule: the outer top of a floating box may not be higher
+// than the outer top of any block or floated box generated by an element
+// earlier in the source document
+NGLogicalOffset AdjustToTopEdgeAlignmentRule(const NGConstraintSpace& space,
+                                             const NGLogicalOffset& offset) {
+  NGLogicalOffset adjusted_offset = offset;
+  LayoutUnit& adjusted_block_offset = adjusted_offset.block_offset;
+  if (space.Exclusions()->last_left_float)
+    adjusted_block_offset =
+        std::max(adjusted_block_offset,
+                 space.Exclusions()->last_left_float->rect.BlockStartOffset());
+  if (space.Exclusions()->last_right_float)
+    adjusted_block_offset =
+        std::max(adjusted_block_offset,
+                 space.Exclusions()->last_right_float->rect.BlockStartOffset());
+  return adjusted_offset;
+}
+
 // Finds a layout opportunity for the fragment.
 // It iterates over all layout opportunities in the constraint space and returns
 // the first layout opportunity that is wider than the fragment or returns the
@@ -99,13 +112,21 @@ NGExclusion CreateExclusion(const NGFragment& fragment,
 // @param space Constraint space that is used to find layout opportunity for
 //              the fragment.
 // @param fragment Fragment that needs to be placed.
+// @param origin_point {@code space}'s offset relative to the space that
+//                     establishes a new formatting context that we're currently
+//                     in and where all our exclusions reside.
 // @param margins Margins of the fragment.
 // @return Layout opportunity for the fragment.
 const NGLayoutOpportunity FindLayoutOpportunityForFragment(
     NGConstraintSpace* space,
     const NGFragment& fragment,
+    const NGLogicalOffset& origin_point,
     const NGBoxStrut& margins) {
-  NGLayoutOpportunityIterator* opportunity_iter = space->LayoutOpportunities();
+  NGLogicalOffset adjusted_origin_point =
+      AdjustToTopEdgeAlignmentRule(*space, origin_point);
+
+  NGLayoutOpportunityIterator* opportunity_iter =
+      space->LayoutOpportunities(adjusted_origin_point);
   NGLayoutOpportunity opportunity;
   NGLayoutOpportunity opportunity_candidate = opportunity_iter->Next();
 
@@ -114,20 +135,19 @@ const NGLayoutOpportunity FindLayoutOpportunityForFragment(
     // Checking opportunity's block size is not necessary as a float cannot be
     // positioned on top of another float inside of the same constraint space.
     auto fragment_inline_size = fragment.InlineSize() + margins.InlineSum();
-    if (opportunity.size.inline_size > fragment_inline_size)
+    if (opportunity.size.inline_size >= fragment_inline_size)
       break;
-
     opportunity_candidate = opportunity_iter->Next();
   }
-
   return opportunity;
 }
 
 // Calculates the logical offset for opportunity.
 NGLogicalOffset CalculateLogicalOffsetForOpportunity(
     const NGLayoutOpportunity& opportunity,
-    LayoutUnit float_offset,
-    NGBoxStrut margins) {
+    const LayoutUnit& float_offset,

[ikilpatrick, 2017/01/26 04:37:26]

drop the reference, this is a single int basically;

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+    const NGBoxStrut& margins,
+    const NGLogicalOffset& space_offset) {
   // Adjust to child's margin.
   LayoutUnit inline_offset = margins.inline_start;
   LayoutUnit block_offset = margins.block_start;
@@ -138,9 +158,58 @@ NGLogicalOffset CalculateLogicalOffsetForOpportunity(
 
   inline_offset += float_offset;
 
+  block_offset -= space_offset.block_offset;
+  inline_offset -= space_offset.inline_offset;
+
   return NGLogicalOffset(inline_offset, block_offset);
 }
 
+// Calculates the relative position(from {@code from_offset}) of the

[ikilpatrick, 2017/01/26 04:37:25]

.nit space "position ("

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+// floating object that is requested to be positioned from {@code origin_point}.
+NGLogicalOffset PositionFloat(const NGLogicalOffset& origin_point,
+                              const NGLogicalOffset& from_offset,
+                              NGFloatingObject* floating_object) {
+  NGConstraintSpace* float_space = floating_object->space;
+  NGBoxFragment* float_fragment =
+      new NGBoxFragment(float_space->WritingMode(), float_space->Direction(),
+                        toNGPhysicalBoxFragment(floating_object->fragment));

[ikilpatrick, 2017/01/26 04:37:25]

DCHECK(floating_object->fragment) ?

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  // Find a layout opportunity that will fit our float.
+  const NGLayoutOpportunity opportunity =
+      FindLayoutOpportunityForFragment(floating_object->space, *float_fragment,
+                                       origin_point, floating_object->margins);
+  DCHECK(!opportunity.IsEmpty()) << "Opportunity is empty but it shouldn't be";
+
+  // Calculate the float offset if needed.
+  LayoutUnit float_offset;
+  if (floating_object->exclusion_type == NGExclusion::kFloatRight) {
+    float_offset = opportunity.size.inline_size - float_fragment->InlineSize();
+  }
+
+  // Add the float as an exclusion.
+  const NGExclusion exclusion = CreateExclusion(
+      *float_fragment, opportunity, float_offset, floating_object->margins,
+      floating_object->exclusion_type);
+  float_space->AddExclusion(exclusion);
+
+  return CalculateLogicalOffsetForOpportunity(
+      opportunity, float_offset, floating_object->margins, from_offset);
+}
+
+// Positions pending floats stored on the fragment builder starting from
+// {@code origin_point}.
+void PositionFloats(const NGLogicalOffset& origin_point,

[ikilpatrick, 2017/01/26 04:37:26]

is "Pending" floats a better name than unpositioned? Then this could be:
PositionPendingFloats?

[Gleb Lanbin, 2017/01/31 00:25:01]

I thought about that. Here is my rationale behind naming this method as
PositionFloats:
- I think the word "unpositioned_floats" implies that it has the list of objects
that need to be positioned. "Pending" is not that descriptive. If I rename
everything to pending_floats then it would not be clear why/what they are
pending for.
- Also I find PositionUnpositionedFloats a bit tautological.

+                    NGFragmentBuilder* builder) {
+  DCHECK(builder->BfcOffset()) << "Parent BFC offset should be known here";
+  NGLogicalOffset from_offset = builder->BfcOffset().value();
+
+  for (auto& floating_object : builder->UnpositionedFloats()) {
+    NGLogicalOffset float_fragment_offset =
+        PositionFloat(origin_point, from_offset, floating_object);
+    builder->AddFloatingObject(floating_object, float_fragment_offset);
+  }
+  builder->MutableUnpositionedFloats().clear();
+}
+
 // Whether an in-flow block-level child creates a new formatting context.
 //
 // This will *NOT* check the following cases:
@@ -190,8 +259,7 @@ NGBlockLayoutAlgorithm::NGBlockLayoutAlgorithm(
       constraint_space_(constraint_space),
       break_token_(break_token),
       builder_(new NGFragmentBuilder(NGPhysicalFragment::kFragmentBox,
-                                     layout_object)),
-      is_fragment_margin_strut_block_start_updated_(false) {
+                                     layout_object)) {
   DCHECK(style_);
 }
 
@@ -222,6 +290,28 @@ bool NGBlockLayoutAlgorithm::ComputeMinAndMaxContentSizes(
   return true;
 }
 
+NGLogicalOffset NGBlockLayoutAlgorithm::PositionFragmentWithKnownBfcOffset(
+    const NGLogicalOffset& offset) {
+  curr_bfc_offset_.block_offset = offset.block_offset;
+  // First block that knows its position. Update the parent's BFC offset.
+  if (!builder_->BfcOffset()) {
+    NGLogicalOffset parent_bfc_offset =
+        ConstraintSpace().IsNewFormattingContext() ? NGLogicalOffset()
+                                                   : curr_bfc_offset_;
+    builder_->SetBfcOffset(parent_bfc_offset);
+  }
+
+  // OK to position pending floats. curr_bfc_offset_ and parent's BFC offset
+  // are accurate here.
+  PositionFloats(curr_bfc_offset_, builder_);
+
+  LayoutUnit block_offset =
+      offset.block_offset - builder_->BfcOffset().value().block_offset;
+  LayoutUnit inline_offset =
+      border_and_padding_.inline_start + curr_child_margins_.inline_start;
+  return {inline_offset, block_offset};
+}
+
 NGPhysicalFragment* NGBlockLayoutAlgorithm::Layout() {
   WTF::Optional<MinAndMaxContentSizes> sizes;
   if (NeedMinAndMaxContentSizes(ConstraintSpace(), Style())) {
@@ -268,6 +358,8 @@ NGPhysicalFragment* NGBlockLayoutAlgorithm::Layout() {
   builder_->SetWritingMode(constraint_space_->WritingMode());
   builder_->SetInlineSize(inline_size).SetBlockSize(block_size);
 
+  // TODO(glebl): fix multicol after the new margin collapsing/floats algorithm
+  // based on BFCOffset is checked in.
   if (NGBlockBreakToken* token = CurrentBlockBreakToken()) {
     // Resume after a previous break.
     content_size_ = token->BreakOffset();
@@ -277,6 +369,19 @@ NGPhysicalFragment* NGBlockLayoutAlgorithm::Layout() {
     current_child_ = first_child_;
   }
 
+  curr_margin_strut_ = constraint_space_->MarginStrut();

[ikilpatrick, 2017/01/26 00:49:58]

ConstraintSpace() instead?

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  curr_bfc_offset_ = ConstraintSpace().BfcOffset();
+
+  // Margins collapsing:
+  //   Do not collapse margins between parent and its child if there is
+  //   border/padding between them

[ikilpatrick, 2017/01/26 00:49:58]

.nit period.

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  if (border_and_padding_.block_start) {
+    curr_bfc_offset_.block_offset += curr_margin_strut_.Collapse();
+    builder_->SetBfcOffset(curr_bfc_offset_);
+    curr_margin_strut_ = NGMarginStrut();
+  }
+  curr_bfc_offset_.block_offset += content_size_;
+
   while (current_child_) {
     EPosition position = current_child_->Style()->position();
     if (position == AbsolutePosition || position == FixedPosition) {
@@ -301,7 +406,16 @@ NGPhysicalFragment* NGBlockLayoutAlgorithm::Layout() {
       break;
   }
 
+  // Margins collapsing:
+  //   Bottom margins of an in-flow block box doesn't collapse with its last
+  //   in-flow block-level child's bottom margin if the box has bottom
+  //   border/padding.
   content_size_ += border_and_padding_.block_end;
+  if (border_and_padding_.block_end ||
+      ConstraintSpace().IsNewFormattingContext()) {
+    content_size_ += curr_margin_strut_.Collapse();
+    curr_margin_strut_ = NGMarginStrut();
+  }
 
   // Recompute the block-axis size now that we know our content size.
   block_size =
@@ -310,6 +424,17 @@ NGPhysicalFragment* NGBlockLayoutAlgorithm::Layout() {
 
   LayoutOutOfFlowChildren();
 
+  // Set offset if the size is not empty.

[ikilpatrick, 2017/01/26 00:49:57]

Set our BFC offset if ... ? (up to you)

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  if (block_size && !builder_->BfcOffset()) {
+    curr_bfc_offset_.block_offset += curr_margin_strut_.Collapse();
+    builder_->SetBfcOffset(curr_bfc_offset_);
+  }
+
+  if (!Style().logicalHeight().isAuto()) {

[ikilpatrick, 2017/01/26 00:49:57]

add comment explaining what's going on here.

[ikilpatrick, 2017/01/26 00:49:58]

TODO(glebl): handle minLogicalHeight, maxLogicalHeight.

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+    curr_margin_strut_ = NGMarginStrut();
+  }
+  builder_->SetEndMarginStrut(curr_margin_strut_);
+
   builder_->SetInlineOverflow(max_inline_size_).SetBlockOverflow(content_size_);
 
   if (ConstraintSpace().HasBlockFragmentation())
@@ -320,23 +445,60 @@ NGPhysicalFragment* NGBlockLayoutAlgorithm::Layout() {
   return fragment;
 }
 
-void NGBlockLayoutAlgorithm::FinishCurrentChildLayout(NGFragment* fragment) {
-  NGBoxStrut child_margins = ComputeMargins(
-      *space_for_current_child_, CurrentChildStyle(),
-      constraint_space_->WritingMode(), constraint_space_->Direction());
-  NGLogicalOffset fragment_offset;
+void NGBlockLayoutAlgorithm::FinishCurrentChildLayout(
+    NGFragment* base_fragment) {
+  const NGBoxFragment& fragment = *toNGBoxFragment(base_fragment);
+  // Pull out unpositioned floats to the current fragment. This may needed if
+  // for example the child fragment could not position its floats because it's
+  // empty and therefore couldn't determine its position in space.
+  builder_->MutableUnpositionedFloats().appendVector(
+      fragment.PhysicalFragment()->UnpositionedFloats());
+
   if (CurrentChildStyle().isFloating()) {
-    fragment_offset = PositionFloatFragment(*fragment, child_margins);
-  } else {
-    ApplyAutoMargins(*space_for_current_child_, CurrentChildStyle(),
-                     fragment->InlineSize(), &child_margins);
-    fragment_offset = PositionFragment(*fragment, child_margins);
+    NGFloatingObject* floating_object = new NGFloatingObject(
+        fragment.PhysicalFragment(), space_for_current_child_, current_child_,
+        CurrentChildStyle(), curr_child_margins_);
+    builder_->AddUnpositionedFloat(floating_object);
+    // No need to postpone the positioning as we know the correct offset.
+    if (builder_->BfcOffset()) {
+      NGLogicalOffset origin_point = curr_bfc_offset_;
+      // Adjust origin point to the margins of the last child.
+      // Example: <div style="margin-bottom: 20px"><float></div>
+      //          <div style="margin-bottom: 30px"></div>
+      origin_point.block_offset += curr_margin_strut_.Collapse();
+      PositionFloats(origin_point, builder_);
+    }
+    return;
   }
+
+  // Collapse empty block's margins.
+  if (!fragment.BlockSize()) {
+    curr_margin_strut_.Append(curr_child_margins_.block_end);
+  }
+
+  NGLogicalOffset fragment_offset = {
+      border_and_padding_.inline_start + curr_child_margins_.inline_start,
+      content_size_};
+  if (fragment.BfcOffset())
+    fragment_offset =
+        PositionFragmentWithKnownBfcOffset(fragment.BfcOffset().value());
+
   if (fragmentainer_mapper_)
     fragmentainer_mapper_->ToVisualOffset(fragment_offset);
   else
     fragment_offset.block_offset -= PreviousBreakOffset();
-  builder_->AddChild(fragment, fragment_offset);
+
+  builder_->AddChild(base_fragment, fragment_offset);
+
+  // Update margin strut.
+  curr_margin_strut_ = fragment.EndMarginStrut();
+  curr_margin_strut_.Append(curr_child_margins_.block_end);
+
+  content_size_ = fragment.BlockSize() + fragment_offset.block_offset;
+  max_inline_size_ =
+      std::max(max_inline_size_, fragment.InlineSize() +
+                                     curr_child_margins_.InlineSum() +
+                                     border_and_padding_.InlineSum());
 }
 
 void NGBlockLayoutAlgorithm::LayoutOutOfFlowChildren() {
@@ -505,133 +667,6 @@ LayoutUnit NGBlockLayoutAlgorithm::SpaceAvailableForCurrentChild() const {
   return space_left;
 }
 
-NGBoxStrut NGBlockLayoutAlgorithm::CollapseMargins(
-    const NGBoxStrut& margins,
-    const NGBoxFragment& fragment) {
-  bool is_zero_height_box = !fragment.BlockSize() && margins.IsEmpty() &&
-                            fragment.MarginStrut().IsEmpty();
-  // Create the current child's margin strut from its children's margin strut or
-  // use margin strut from the the last non-empty child.
-  NGDeprecatedMarginStrut curr_margin_strut =
-      is_zero_height_box ? prev_child_margin_strut_ : fragment.MarginStrut();
-
-  // Calculate borders and padding for the current child.
-  NGBoxStrut border_and_padding =
-      ComputeBorders(CurrentChildStyle()) +
-      ComputePadding(ConstraintSpace(), CurrentChildStyle());
-
-  // Collapse BLOCK-START margins if there is no padding or border between
-  // parent (current child) and its first in-flow child.
-  if (border_and_padding.block_start) {
-    curr_margin_strut.SetMarginBlockStart(margins.block_start);
-  } else {
-    curr_margin_strut.AppendMarginBlockStart(margins.block_start);
-  }
-
-  // Collapse BLOCK-END margins if
-  // 1) there is no padding or border between parent (current child) and its
-  //    first/last in-flow child
-  // 2) parent's logical height is auto.
-  if (CurrentChildStyle().logicalHeight().isAuto() &&
-      !border_and_padding.block_end) {
-    curr_margin_strut.AppendMarginBlockEnd(margins.block_end);
-  } else {
-    curr_margin_strut.SetMarginBlockEnd(margins.block_end);
-  }
-
-  NGBoxStrut result_margins;
-  // Margins of the newly established formatting context do not participate
-  // in Collapsing Margins:
-  // - Compute margins block start for adjoining blocks *including* 1st block.
-  // - Compute margins block end for the last block.
-  // - Do not set the computed margins to the parent fragment.
-  if (constraint_space_->IsNewFormattingContext()) {
-    result_margins.block_start = ComputeCollapsedMarginBlockStart(
-        prev_child_margin_strut_, curr_margin_strut);
-    bool is_last_child = !current_child_->NextSibling();
-    if (is_last_child)
-      result_margins.block_end = curr_margin_strut.BlockEndSum();
-    return result_margins;
-  }
-
-  // Zero-height boxes are ignored and do not participate in margin collapsing.
-  if (is_zero_height_box)
-    return result_margins;
-
-  // Compute the margin block start for adjoining blocks *excluding* 1st block
-  if (is_fragment_margin_strut_block_start_updated_) {
-    result_margins.block_start = ComputeCollapsedMarginBlockStart(
-        prev_child_margin_strut_, curr_margin_strut);
-  }
-
-  // Update the parent fragment's margin strut
-  UpdateMarginStrut(curr_margin_strut);
-
-  prev_child_margin_strut_ = curr_margin_strut;
-  return result_margins;
-}
-
-NGLogicalOffset NGBlockLayoutAlgorithm::PositionFragment(
-    const NGFragment& fragment,
-    const NGBoxStrut& margins) {
-  const NGBoxStrut collapsed_margins =
-      CollapseMargins(margins, toNGBoxFragment(fragment));
-
-  AdjustToClearance(ConstraintSpace(), CurrentChildStyle(), &content_size_);
-
-  LayoutUnit inline_offset =
-      border_and_padding_.inline_start + margins.inline_start;
-  LayoutUnit block_offset = content_size_ + collapsed_margins.block_start;
-
-  content_size_ += fragment.BlockSize() + collapsed_margins.BlockSum();
-  max_inline_size_ =
-      std::max(max_inline_size_, fragment.InlineSize() + margins.InlineSum() +
-                                     border_and_padding_.InlineSum());
-  return NGLogicalOffset(inline_offset, block_offset);
-}
-
-NGLogicalOffset NGBlockLayoutAlgorithm::PositionFloatFragment(
-    const NGFragment& fragment,
-    const NGBoxStrut& margins) {
-  // TODO(glebl@chromium.org): Support the top edge alignment rule.
-  // Find a layout opportunity that will fit our float.
-
-  // Update offset if there is a clearance.
-  NGLogicalOffset offset = CurrentChildConstraintSpace().Offset();
-  AdjustToClearance(ConstraintSpace(), CurrentChildStyle(),
-                    &offset.block_offset);
-  space_for_current_child_->SetOffset(offset);
-
-  const NGLayoutOpportunity opportunity = FindLayoutOpportunityForFragment(
-      space_for_current_child_, fragment, margins);
-  DCHECK(!opportunity.IsEmpty()) << "Opportunity is empty but it shouldn't be";
-
-  NGExclusion::Type exclusion_type = NGExclusion::kFloatLeft;
-  // Calculate the float offset if needed.
-  LayoutUnit float_offset;
-  if (CurrentChildStyle().floating() == EFloat::kRight) {
-    float_offset = opportunity.size.inline_size - fragment.InlineSize();
-    exclusion_type = NGExclusion::kFloatRight;
-  }
-
-  // Add the float as an exclusion.
-  const NGExclusion exclusion = CreateExclusion(
-      fragment, opportunity, float_offset, margins, exclusion_type);
-  constraint_space_->AddExclusion(exclusion);
-
-  return CalculateLogicalOffsetForOpportunity(opportunity, float_offset,
-                                              margins);
-}
-
-void NGBlockLayoutAlgorithm::UpdateMarginStrut(
-    const NGDeprecatedMarginStrut& from) {
-  if (!is_fragment_margin_strut_block_start_updated_) {
-    builder_->SetMarginStrutBlockStart(from);
-    is_fragment_margin_strut_block_start_updated_ = true;
-  }
-  builder_->SetMarginStrutBlockEnd(from);
-}
-
 NGBoxStrut NGBlockLayoutAlgorithm::CalculateMargins(
     const NGConstraintSpace& space,
     const ComputedStyle& style) {
@@ -660,10 +695,9 @@ NGBlockLayoutAlgorithm::CreateConstraintSpaceForCurrentChild() {
   bool shrink_to_fit = CurrentChildStyle().display() == EDisplay::InlineBlock ||
                        CurrentChildStyle().isFloating();
   DCHECK(current_child_);
-  space_builder_
-      ->SetIsNewFormattingContext(
-          IsNewFormattingContextForInFlowBlockLevelChild(ConstraintSpace(),
-                                                         CurrentChildStyle()))
+  bool is_new_bfc = IsNewFormattingContextForInFlowBlockLevelChild(
+      ConstraintSpace(), CurrentChildStyle());
+  space_builder_->SetIsNewFormattingContext(is_new_bfc)
       .SetIsShrinkToFit(shrink_to_fit)
       .SetWritingMode(
           FromPlatformWritingMode(CurrentChildStyle().getWritingMode()))
@@ -674,11 +708,41 @@ NGBlockLayoutAlgorithm::CreateConstraintSpaceForCurrentChild() {
   curr_child_margins_ = CalculateMargins(*space_builder_->ToConstraintSpace(),
                                          CurrentChildStyle());
 
-  NGConstraintSpace* child_space = space_builder_->ToConstraintSpace();
+  // Clearance :
+  // - Collapse margins
+  // - Update curr_bfc_offset and parent BFC offset if needed.
+  // - Position all pending floats as position is known now.

[ikilpatrick, 2017/01/26 04:37:25]

maybe a note/todo that we don't think this will work with a clear: left , and an
intruding right?

E.g. something along the lines of.... 
https://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E...

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  if (CurrentChildStyle().clear()) {
+    curr_bfc_offset_.block_offset += curr_margin_strut_.Collapse();
+    if (!builder_->BfcOffset()) {
+      builder_->SetBfcOffset(curr_bfc_offset_);
+    }
+    // Only collapse margins if it's an adjoining block with clearance.
+    if (!content_size_) {
+      curr_margin_strut_ = NGMarginStrut();
+      curr_child_margins_.block_start = LayoutUnit();
+    }
+    PositionFloats(curr_bfc_offset_, builder_);
+    AdjustToClearance(constraint_space_->Exclusions(), CurrentChildStyle(),
+                      builder_->BfcOffset().value(), &content_size_);
+  }
+
+  // Collapse the current margin strut with child's block start margin.

[ikilpatrick, 2017/01/26 04:37:25]

s/Collapse/Append? or maybe we should rename NGMarginStrut::Collapse to Sum? (up
to you).

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  // non empty border/padding use cases are handled inside of the child's layout

[ikilpatrick, 2017/01/26 04:37:26]

.nit capital N, period.

[Gleb Lanbin, 2017/01/31 00:25:01]

Done.

+  curr_margin_strut_.Append(curr_child_margins_.block_start);
+  space_builder_->SetMarginStrut(curr_margin_strut_);
+
+  // Set estimated BFC offset to the next child's constraint space.
+  curr_bfc_offset_ = builder_->BfcOffset() ? builder_->BfcOffset().value()
+                                           : ConstraintSpace().BfcOffset();
+  curr_bfc_offset_.block_offset += content_size_;
+  curr_bfc_offset_.inline_offset += border_and_padding_.inline_start;
+  if (ConstraintSpace().IsNewFormattingContext()) {
+    curr_bfc_offset_.inline_offset += curr_child_margins_.inline_start;
+  }
+  space_builder_->SetBfcOffset(curr_bfc_offset_);
 
-  // TODO(layout-ng): Set offset through the space builder.
-  child_space->SetOffset(GetChildSpaceOffset());
-  return child_space;
+  return space_builder_->ToConstraintSpace();
 }
 
 DEFINE_TRACE(NGBlockLayoutAlgorithm) {