[LayoutNG] A different approach to multi-col.

third_party/WebKit/Source/core/layout/ng/ng_paged_layout_algorithm.h

+// Copyright 2017 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 NGPagedLayoutAlgorithm_h
+#define NGPagedLayoutAlgorithm_h
+
+#include "core/CoreExport.h"
+#include "core/layout/ng/geometry/ng_margin_strut.h"
+#include "core/layout/ng/ng_block_node.h"
+#include "core/layout/ng/ng_constraint_space_builder.h"
+#include "core/layout/ng/ng_fragment_builder.h"
+#include "core/layout/ng/ng_layout_algorithm.h"
+
+namespace blink {
+
+class ComputedStyle;
+class NGBlockBreakToken;
+class NGConstraintSpace;
+class NGLayoutResult;
+
+// A class for general block layout (e.g. a <div> with no special style).
+// Lays out the children in sequence.
+class CORE_EXPORT NGPagedLayoutAlgorithm : public NGLayoutAlgorithm {
+ 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.
+  NGPagedLayoutAlgorithm(NGBlockNode* node,
+                         NGConstraintSpace* space,
+                         NGBlockBreakToken* break_token = nullptr);
+
+  Optional<MinMaxContentSize> ComputeMinMaxContentSize() const override;
+  RefPtr<NGLayoutResult> Layout() override;
+
+ private:
+  NGBoxStrut CalculateMargins(NGBlockNode* child,
+                              const NGConstraintSpace& space);
+
+  // Creates a new constraint space for the current child.
+  RefPtr<NGConstraintSpace> CreateConstraintSpaceForChild(NGLayoutInputNode*);
+  void PrepareChildLayout(NGLayoutInputNode*);
+  void FinishChildLayout(NGLayoutInputNode*,
+                         NGConstraintSpace*,
+                         RefPtr<NGLayoutResult>);
+
+  // 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();
+
+  // Calculates logical offset for the current fragment using either
+  // {@code content_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 WTF::Optional<NGLogicalOffset>& known_fragment_offset);
+
+  // Updates the fragment's BFC offset if it's not already set.
+  void UpdateFragmentBfcOffset(const NGLogicalOffset& offset);
+
+  NGLogicalOffset GetChildSpaceOffset() const {
+    return NGLogicalOffset(border_and_padding_.inline_start, content_size_);
+  }
+
+  const NGConstraintSpace& ConstraintSpace() const {
+    DCHECK(constraint_space_);
+    return *constraint_space_;
+  }
+
+  const ComputedStyle& Style() const { return node_->Style(); }
+
+  Persistent<NGBlockNode> node_;
+  NGConstraintSpace* constraint_space_;
+
+  // The break token from which we are currently resuming layout.
+  NGBlockBreakToken* break_token_;
+
+  NGFragmentBuilder builder_;
+  NGConstraintSpaceBuilder space_builder_;
+
+  NGBoxStrut border_and_padding_;
+  LayoutUnit content_size_;
+  LayoutUnit max_inline_size_;
+  // MarginStrut for the previous child.
+  NGMarginStrut curr_margin_strut_;
+  NGLogicalOffset curr_bfc_offset_;
+  NGBoxStrut curr_child_margins_;
+};
+
+}  // namespace blink
+
+#endif  // NGPagedLayoutAlgorithm_h