[LayoutNG] Initial support for multicol, introducing NGBlockBreakToken.

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/ng_block_node.h"
 #include "core/layout/ng/ng_layout_algorithm.h"
 #include "core/layout/ng/ng_units.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 class ComputedStyle;
+class NGBlockBreakToken;
 class NGBreakToken;
+class NGColumnMapper;
 class NGConstraintSpace;
 class NGConstraintSpaceBuilder;
 class NGBoxFragment;
 class NGFragmentBuilder;
 class NGOutOfFlowLayoutPart;
 class NGPhysicalFragment;
 
 // 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 {
@@ skipping 15 matching lines @@
                         NGLayoutAlgorithm**) override;
 
   DECLARE_VIRTUAL_TRACE();
 
  private:
   // Creates a new constraint space for the current child.
   NGConstraintSpace* CreateConstraintSpaceForCurrentChild() const;
   void FinishCurrentChildLayout(NGFragment* fragment);
   bool LayoutOutOfFlowChild();
 
+  // Proceed to the next sibling that still needs layout.
+  //
+  // @param child_fragment The newly created fragment for the current child.
+  // @return true if we can continue to lay out, or false if we need to abort
+  // due to a fragmentainer break.
+  bool ProceedToNextUnfinishedSibling(NGPhysicalFragment* child_fragment);
+
+  // Set a break token which contains enough information to be able to resume
+  // layout in the next fragmentainer.
+  void SetPendingBreakToken(NGBlockBreakToken*);
+
+  // Check if we have a pending break token set. Once we have set a pending
+  // break token, we cannot set another one. First we need to abort layout in
+  // the current fragmentainer and resume in the next one.
+  bool HasPendingBreakToken() const;
+
+  // Final adjusstments 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();
+
+  // Return the break token, if any, at which we resumed layout after a
+  // previous break.
+  NGBlockBreakToken* CurrentBlockBreakToken() const;
+
+  // Return the block offset of the previous break, in the fragmented flow
+  // coordinate space, relatively to the start edge of this block.
+  LayoutUnit PreviousBreakOffset() const;
+
+  // Return the offset of the potential next break, in the fragmented flow
+  // coordinate space, relatively to the start edge of this block.
+  LayoutUnit NextBreakOffset() const;
+
+  // Get the amount of block space left in the current fragmentainer for the
+  // child that is about to be laid out.
+  LayoutUnit SpaceAvailableForCurrentChild() const;
+
+  LayoutUnit BorderEdgeForCurrentChild() const {
+    // TODO(mstensho): Need to take care of margin collapsing somehow. We
+    // should at least attempt to estimate what the top margin is going to be.
+    return content_size_;
+  }
+
   // Computes collapsed margins for 2 adjoining blocks and updates the resultant
   // fragment's MarginStrut if needed.
   // See https://www.w3.org/TR/CSS2/box.html#collapsing-margins
   //
   // @param child_margins Margins information for the current child.
   // @param fragment Current child's fragment.
   // @return NGBoxStrut with margins block start/end.
   NGBoxStrut CollapseMargins(const NGBoxStrut& child_margins,
                              const NGBoxFragment& fragment);
 
@@ skipping 45 matching lines @@
     kStateOutOfFlowLayout,
     kStateFinalize
   };
   LayoutState layout_state_;
   LayoutState compute_minmax_state_;
 
   RefPtr<const ComputedStyle> style_;
 
   Member<NGBlockNode> first_child_;
   Member<NGConstraintSpace> constraint_space_;
+
+  // The break token from which we are currently resuming layout.
   Member<NGBreakToken> break_token_;
+
   Member<NGFragmentBuilder> builder_;
   Member<NGConstraintSpaceBuilder> space_builder_;
   Member<NGConstraintSpace> space_for_current_child_;
   Member<NGBlockNode> current_child_;
   Member<NGBlockNode> current_minmax_child_;
   MinAndMaxContentSizes pending_minmax_sizes_;
 
   Member<NGOutOfFlowLayoutPart> out_of_flow_layout_;
   HeapLinkedHashSet<WeakMember<NGBlockNode>> out_of_flow_candidates_;
   Vector<NGStaticPosition> out_of_flow_candidate_positions_;
   size_t out_of_flow_candidate_positions_index_;
 
+  Member<NGColumnMapper> fragmentainer_mapper_;
+
   NGBoxStrut border_and_padding_;
   LayoutUnit content_size_;
   LayoutUnit max_inline_size_;
   // MarginStrut for the previous child.
   NGMarginStrut prev_child_margin_strut_;
   // Whether the block-start was set for the currently built
   // fragment's margin strut.
   bool is_fragment_margin_strut_block_start_updated_ : 1;
 };
 
 }  // namespace blink
 
 #endif  // NGBlockLayoutAlgorithm_h