[LayoutNG] Fragmentation-aware border+scrollbar+padding strut.

Simplifies the code.

Follow-up to CL:1903193

Change-Id: If5e068a96de44aa938fd3ab83496f1ca757d2dd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1908538Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714406}

third_party/blink/renderer/core/layout/ng/ng_block_layout_algorithm.cc

@@ -181,6 +181,7 @@ NGBlockLayoutAlgorithm::NGBlockLayoutAlgorithm(
       is_resuming_(IsResumingLayout(params.break_token)),
       exclusion_space_(params.space.ExclusionSpace()),
       early_break_(params.early_break) {
+  AdjustForFragmentation(BreakToken(), &border_scrollbar_padding_);
   container_builder_.SetIsNewFormattingContext(
       params.space.IsNewFormattingContext());
   container_builder_.SetInitialFragmentGeometry(params.fragment_geometry);
@@ -462,10 +463,7 @@ inline scoped_refptr<const NGLayoutResult> NGBlockLayoutAlgorithm::Layout(
     container_builder_.SetAdjoiningObjectTypes(adjoining_object_types);
   }
 
-  // If we are resuming from a break token our start border and padding is
-  // within a previous fragment.
-  LayoutUnit content_edge =
-      is_resuming_ ? LayoutUnit() : border_scrollbar_padding_.block_start;
+  LayoutUnit content_edge = border_scrollbar_padding_.block_start;
 
   NGPreviousInflowPosition previous_inflow_position = {
       LayoutUnit(), ConstraintSpace().MarginStrut(),

third_party/blink/renderer/core/layout/ng/ng_block_layout_algorithm.h

@@ -337,7 +337,12 @@ class CORE_EXPORT NGBlockLayoutAlgorithm
   // Returns kIndefiniteSize in all other cases.
   LayoutUnit CalculateMinimumBlockSize(const NGMarginStrut& end_margin_strut);
 
+  // Border + padding sum, resolved from the node's computed style.
   const NGBoxStrut border_padding_;
+
+  // Border + scrollbar + padding sum for the fragment to be generated (most
+  // importantly, for non-first fragments, leading block border + scrollbar +
+  // padding is zero).
   NGBoxStrut border_scrollbar_padding_;
 
   LogicalSize child_available_size_;

third_party/blink/renderer/core/layout/ng/ng_column_layout_algorithm.cc

@@ -95,6 +95,7 @@ NGColumnLayoutAlgorithm::NGColumnLayoutAlgorithm(
                       params.fragment_geometry.padding),
       border_scrollbar_padding_(border_padding_ +
                                 params.fragment_geometry.scrollbar) {
+  AdjustForFragmentation(BreakToken(), &border_scrollbar_padding_);
   container_builder_.SetIsNewFormattingContext(
       params.space.IsNewFormattingContext());
   container_builder_.SetInitialFragmentGeometry(params.fragment_geometry);
@@ -135,9 +136,7 @@ scoped_refptr<const NGLayoutResult> NGColumnLayoutAlgorithm::Layout() {
 
   container_builder_.SetIsBlockFragmentationContextRoot();
 
-  // Omit leading border+padding+scrollbar for all fragments but the first.
-  if (!IsResumingLayout(BreakToken()))
-    intrinsic_block_size_ = border_scrollbar_padding_.block_start;
+  intrinsic_block_size_ = border_scrollbar_padding_.block_start;
 
   if (!LayoutChildren()) {
     // We need to discard this layout and do it again. We found an earlier break
@@ -376,8 +375,8 @@ scoped_refptr<const NGLayoutResult> NGColumnLayoutAlgorithm::LayoutRow(
   // fragmentation context.
   if (is_constrained_by_outer_fragmentation_context_ &&
       column_size.block_size != kIndefiniteSize) {
-    column_size.block_size -= ConsumedBlockSizeInContentBox(
-        border_scrollbar_padding_.block_start, BreakToken());
+    if (BreakToken())
+      column_size.block_size -= BreakToken()->ConsumedBlockSize();
 
     // Subtract the space already taken in the current fragment (spanners and
     // earlier column rows).
@@ -858,14 +857,6 @@ LayoutUnit NGColumnLayoutAlgorithm::ConstrainColumnBlockSize(
   return size - extra;
 }
 
-LayoutUnit NGColumnLayoutAlgorithm::CurrentContentBlockOffset() const {
-  // If we're past the block-start border and padding, this is simple:
-  if (IsResumingLayout(BreakToken()))
-    return intrinsic_block_size_;
-  // Otherwise subtract those.
-  return intrinsic_block_size_ - border_scrollbar_padding_.block_start;
-}
-
 void NGColumnLayoutAlgorithm::FinishAfterBreakBeforeSpanner(
     scoped_refptr<const NGBlockBreakToken> next_column_token) {
   // We broke before the spanner. We're done here. Take up the remaining space

third_party/blink/renderer/core/layout/ng/ng_column_layout_algorithm.h

@@ -62,7 +62,9 @@ class CORE_EXPORT NGColumnLayoutAlgorithm
                                     LayoutUnit current_column_size) const;
 
   LayoutUnit ConstrainColumnBlockSize(LayoutUnit size) const;
-  LayoutUnit CurrentContentBlockOffset() const;
+  LayoutUnit CurrentContentBlockOffset() const {
+    return intrinsic_block_size_ - border_scrollbar_padding_.block_start;
+  }
 
   // Finalize layout after breaking before a spanner.
   void FinishAfterBreakBeforeSpanner(
@@ -87,8 +89,14 @@ class CORE_EXPORT NGColumnLayoutAlgorithm
   // When set, this will specify where to break before or inside.
   const NGEarlyBreak* early_break_ = nullptr;
 
+  // Border + padding sum, resolved from the node's computed style.
   const NGBoxStrut border_padding_;
-  const NGBoxStrut border_scrollbar_padding_;
+
+  // Border + scrollbar + padding sum for the fragment to be generated (most
+  // importantly, for non-first fragments, leading block border + scrollbar +
+  // padding is zero).
+  NGBoxStrut border_scrollbar_padding_;
+
   LogicalSize content_box_size_;
   int used_column_count_;
   LayoutUnit column_inline_size_;

third_party/blink/renderer/core/layout/ng/ng_fragmentation_utils.h

@@ -5,6 +5,7 @@
 #ifndef THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_NG_NG_FRAGMENTATION_UTILS_H_
 #define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_NG_NG_FRAGMENTATION_UTILS_H_
 
+#include "third_party/blink/renderer/core/layout/ng/geometry/ng_box_strut.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_block_break_token.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_block_node.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_box_fragment_builder.h"
@@ -72,6 +73,18 @@ inline LayoutUnit FragmentainerSpaceAtBfcStart(const NGConstraintSpace& space) {
   return space.FragmentainerBlockSize() - space.FragmentainerOffsetAtBfc();
 }
 
+// Adjust the border+scrollbar+padding strut for fragmentation. Leading
+// border+scrollbar+padding should only take up space in the first fragment
+// generated from a node.
+inline void AdjustForFragmentation(const NGBlockBreakToken* break_token,
+                                   NGBoxStrut* border_scrollbar_padding) {
+  if (LIKELY(!break_token))
+    return;
+  if (break_token->IsBreakBefore())
+    return;
+  border_scrollbar_padding->block_start = LayoutUnit();
+}
+
 // Set up a child's constraint space builder for block fragmentation. The child
 // participates in the same fragmentation context as parent_space. If the child
 // establishes a new formatting context, new_bfc_block_offset must be set to the

third_party/blink/renderer/core/layout/ng/ng_length_utils.cc

@@ -8,7 +8,6 @@
 #include "base/optional.h"
 #include "third_party/blink/renderer/core/layout/layout_box.h"
 #include "third_party/blink/renderer/core/layout/layout_table_cell.h"
-#include "third_party/blink/renderer/core/layout/ng/ng_block_break_token.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_block_node.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_constraint_space.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_constraint_space_builder.h"
@@ -1272,18 +1271,4 @@ base::Optional<MinMaxSize> CalculateMinMaxSizesIgnoringChildren(
   return base::nullopt;
 }
 
-LayoutUnit ConsumedBlockSizeInContentBox(
-    LayoutUnit border_scrollbar_padding_block_start,
-    const NGBlockBreakToken* break_token) {
-  if (!break_token)
-    return LayoutUnit();
-  LayoutUnit consumed_block_size =
-      break_token->ConsumedBlockSize() - border_scrollbar_padding_block_start;
-  // There are no valid break points inside borders and padding, but if the
-  // fragmentainer is actually shorter than the space taken up bby borders
-  // and/or padding, we may end up slicing them into multiple fragmentainers
-  // anyway - in which case the size we just calculated becomes negative.
-  return consumed_block_size.ClampNegativeToZero();
-}
-
 }  // namespace blink

third_party/blink/renderer/core/layout/ng/ng_length_utils.h

@@ -24,7 +24,6 @@ class ComputedStyle;
 class Length;
 struct MinMaxSizeInput;
 class NGConstraintSpace;
-class NGBlockBreakToken;
 class NGBlockNode;
 class NGLayoutInputNode;
 
@@ -483,11 +482,6 @@ base::Optional<MinMaxSize> CalculateMinMaxSizesIgnoringChildren(
     const NGBoxStrut& border_scrollbar_padding,
     NGMinMaxSizeType);
 
-// Return the sum of the block-size of the content-boxes in all preceding
-// fragments.
-LayoutUnit ConsumedBlockSizeInContentBox(
-    LayoutUnit border_scrollbar_padding_block_start,
-    const NGBlockBreakToken*);
 
 }  // namespace blink