Fix Border collapsing with colpsan / rowspan cells

third_party/WebKit/Source/core/paint/TableCollapsedBorderPainter.cpp

+// Copyright 2014 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.
+#include "core/paint/TableCollapsedBorderPainter.h"
+#include <algorithm>
+#include "core/layout/LayoutTableCell.h"
+#include "core/layout/LayoutTableCol.h"
+#include "core/paint/BlockPainter.h"
+#include "core/paint/BoxPainter.h"
+#include "core/paint/LayoutObjectDrawingRecorder.h"
+#include "core/paint/ObjectPainter.h"
+#include "core/paint/PaintInfo.h"
+#include "platform/graphics/GraphicsContextStateSaver.h"
+
+namespace blink {
+// Comparator: returns
+// -1 => e1 <  e2
+//  0 => e1 == e2
+//  1 => e1 >  e2
+static int CompareEdges(const TableCollapsedBorderPainter::EdgeRecord& e1,
+                        const TableCollapsedBorderPainter::EdgeRecord& e2) {
+  // if (!e1.border_) {
+  //     if (!e2.border_)
+  //         return 0;
+  //     else
+  //         return -1;
+  // }
+  // if (!e2.border_)
+  //     return 1;
+  EBorderStyle e1_style = e1.border_.Style();
+  EBorderStyle e2_style = e2.border_.Style();
+  // RULES: https://www.w3.org/TR/CSS2/tables.html#border-conflict-resolution
+  // 1) Hidden edges win
+  // 2) None edges lose
+  // 3) Wider border-width win
+  // 4) Louder border-style win
+  // 5) Higher precedence wins
+  // Rule #1
+  if (e1_style == kBorderStyleHidden) {
+    if (e2_style == kBorderStyleHidden)
+      return 0;
+    // else
+    return 1;
+  }
+  if (e2_style == kBorderStyleHidden)
+    return -1;
+  // Rule #2
+  if (e1_style == kBorderStyleNone) {
+    if (e2_style == kBorderStyleNone)
+      return 0;
+    // else
+    return -1;
+  }
+  if (e2_style == kBorderStyleNone)
+    return 1;
+  // Rule #3
+  if (e1.border_.Width() < e2.border_.Width())
+    return -1;
+  // else
+  if (e2.border_.Width() < e1.border_.Width())
+    return 1;
+  // Rule #4
+  if (e1_style > e2_style)
+    return 1;
+  // else
+  if (e2_style > e1_style)
+    return -1;
+  // Rule #5
+  if (e1.precedence_ != e2.precedence_)
+    return e1.precedence_ < e2.precedence_ ? -1 : 1;
+  return 0;
+}
+
+// Like CompareEdges, except that HIDDEN edges lose
+static int CompareIntersectionEdges(
+    const TableCollapsedBorderPainter::EdgeRecord& e1,
+    const TableCollapsedBorderPainter::EdgeRecord& e2) {
+  EBorderStyle e1_style = e1.border_.Style();
+  EBorderStyle e2_style = e2.border_.Style();
+  // Rule #1
+  if (e1_style == kBorderStyleHidden) {
+    if (e2_style == kBorderStyleHidden)
+      return 0;
+    // else
+    return -1;
+  }
+  if (e2_style == kBorderStyleHidden)
+    return 1;
+  return CompareEdges(e1, e2);
+}
+
+static std::string DirectionToStr(
+    TableCollapsedBorderPainter::EdgeDirection dir) {
+  switch (dir) {
+    case TableCollapsedBorderPainter::North:
+      return "North";
+    case TableCollapsedBorderPainter::West:
+      return "West";
+    case TableCollapsedBorderPainter::East:
+      return "East";
+    case TableCollapsedBorderPainter::South:
+      return "South";
+    case TableCollapsedBorderPainter::None:
+      return "None";
+  }
+}
+
+static std::string PrecedenceToStr(EBorderPrecedence p) {
+  switch (p) {
+    case kBorderPrecedenceOff:
+      return "OFF";
+    case kBorderPrecedenceTable:
+      return "TABLE";
+    case kBorderPrecedenceColumnGroup:
+      return "COLGROUP";
+    case kBorderPrecedenceColumn:
+      return "COL";
+    case kBorderPrecedenceRowGroup:
+      return "ROWGROUP";
+    case kBorderPrecedenceRow:
+      return "ROW";
+    case kBorderPrecedenceCell:
+      return "CELL";
+  }
+}
+
+void TableCollapsedBorderPainter::ShowEdge(unsigned row,
+                                           unsigned col,
+                                           EdgeDirection direction,
+                                           EBorderPrecedence precedence,
+                                           const BorderValue& border,
+                                           Color resolved_color) const {
+  Color c = border.GetColor().Resolve(resolved_color);
+  LOG(INFO) << "[" << row << " " << col << " " << DirectionToStr(direction)
+            << "] " << PrecedenceToStr(precedence) << " " << border.Width()
+            << " " << c.SerializedAsCSSComponentValue().Ascii().data();
+}
+
+void TableCollapsedBorderPainter::ShowEdges(bool show_hidden) const {
+  LOG(INFO) << "edges";
+  for (auto r = start_visible_row_; r <= end_visible_row_; r++) {
+    LOG(INFO) << "row:" << r;
+    for (auto c = start_visible_column_; c < end_visible_column_; c++) {
+      auto edgeIdx = EdgeToIndex(r, c, East);
+      if (edgeIdx != npos) {
+        EdgeRecord edge = edges_[edgeIdx];
+        if (show_hidden || edge.precedence_ != kBorderPrecedenceOff) {
+          ShowEdge(r, c, East, edge.precedence_, edge.border_,
+                   edge.resolved_color_);
+        }
+      }
+      edgeIdx = EdgeToIndex(r, c, South);
+      if (edgeIdx != npos) {
+        EdgeRecord edge = edges_[edgeIdx];
+        if (show_hidden || edge.precedence_ != kBorderPrecedenceOff) {
+          ShowEdge(r, c, South, edge.precedence_, edge.border_,
+                   edge.resolved_color_);
+        }
+      }
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::ShowVisibleEdges(
+    const VisibleEdgeContainer& edges) const {
+  LOG(INFO) << "visedges";
+  for (auto edge = edges.begin(); edge < edges.end(); edge++) {
+    ShowEdge((*edge).m_row, (*edge).m_column, (*edge).direction_,
+             (*edge).precedence_, (*edge).border_, (*edge).resolved_color_);
+  }
+}
+
+void TableCollapsedBorderPainter::ShowIntersection(unsigned row,
+                                                   unsigned col) const {
+  auto i = IntersectionToIndex(row, col);
+  if (i != npos) {
+    const Intersection in = intersections_[i];
+    if (in.direction_ != None) {
+      LOG(INFO) << "[" << row << ", " << col << "] " << in.width_.ToInt() << " "
+                << in.height_.ToInt()
+                << " Win:" << DirectionToStr(in.direction_);
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::ShowIntersections() const {
+  LOG(INFO) << "intersections";
+  for (auto r = start_visible_row_; r <= end_visible_row_; r++) {
+    for (auto c = start_visible_column_; c < end_visible_column_; c++) {
+      ShowIntersection(r, c);
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::PaintBorders(
+    const PaintInfo& paint_info,
+    const LayoutPoint& paint_offset,
+    const CellSpan& dirty_rows,
+    const CellSpan& dirty_columns,
+    const TableCollapsedBorderPainter& previous_painter) {
+  InitEdges(dirty_rows, dirty_columns, previous_painter);
+  // draw all the edges
+  // initial algorithm: just draw everything
+  // later algorithms: draw continuous lines if possible
+  InitIntersections();
+  PaintEdges(paint_info, paint_offset, dirty_rows, dirty_columns);
+}
+
+void TableCollapsedBorderPainter::InitEdges(
+    const CellSpan& dirty_rows,
+    const CellSpan& dirty_columns,
+    const TableCollapsedBorderPainter& previous_painter) {
+  // Initialize sizes
+  // number of rows/cols in the section
+  num_rows_ = layout_table_section_->NumRows();
+  num_effective_columns_ =
+      layout_table_section_->Table()->NumEffectiveColumns();
+  // Coordinates of intersections whose edges we'd like to measure.
+  // Measurement area is dirty_rows x dirtyCols + single-cell wide border zone
+  // above/left of dirty area.
+  //
+  // Border zone is needed to measure intersections inside dirty area correctly.
+  //
+  // Number of intersections inside n-rows is n+1, inside m-cols is m+1
+  // start and end. End points to one beyond, equivalent to iterator's .end()
+  start_visible_row_ = dirty_rows.Start() == 0 ? 0 : dirty_rows.Start() - 1;
+  start_visible_column_ =
+      dirty_columns.Start() == 0 ? 0 : dirty_columns.Start() - 1;
+  end_visible_row_ = dirty_rows.end() + 1;
+  end_visible_column_ = dirty_columns.end() + 1;
+  unsigned edgeRowCount = end_visible_row_ - start_visible_row_;
+  unsigned edgeColumnCount = end_visible_column_ - start_visible_column_;
+  edges_.Resize(2 * edgeRowCount * edgeColumnCount);
+  PopulateEdges(dirty_rows, dirty_columns, previous_painter);
+  // ShowEdges();
+}
+
+void TableCollapsedBorderPainter::InitIntersections() {
+  max_intersection_width_ = 0;
+  max_intersection_height_ = 0;
+  intersections_.Resize((end_visible_row_ - start_visible_row_) *
+                        (end_visible_column_ - start_visible_column_));
+  for (unsigned r = start_visible_row_; r < end_visible_row_; r++) {
+    for (unsigned c = start_visible_column_; c < end_visible_column_; c++) {
+      InitIntersection(r, c);
+    }
+  }
+  // ShowIntersections();
+}
+
+void TableCollapsedBorderPainter::InitIntersection(unsigned row, unsigned col) {
+  EdgeRecord edges[None];
+  for (int d = North; d < None; d++) {
+    unsigned index = EdgeToIndex(row, col, (EdgeDirection)d);
+    if (index != npos)
+      edges[d] = edges_[index];
+  }
+  EdgeDirection winner = North;
+  for (int d = West; d < None; d++) {
+    if (CompareIntersectionEdges(edges[winner], edges[d]) == -1)
+      winner = (EdgeDirection)d;
+  }
+  unsigned index = IntersectionToIndex(row, col);
+  // only set if our winner is really an edge
+  if (edges[winner].precedence_ != kBorderPrecedenceOff) {
+    unsigned width = 0;
+    unsigned height = 0;
+    if (winner == North || winner == South) {
+      width = edges[winner].border_.Width();
+      if (CompareIntersectionEdges(edges[East], edges[West]) < 1)  // West won
+        height = edges[West].border_.Width();
+      else
+        height = edges[East].border_.Width();
+    } else {  // winner == East || West
+      height = edges[winner].border_.Width();
+      if (CompareIntersectionEdges(edges[North], edges[South]) <
+          1)  // South won
+        width = edges[South].border_.Width();
+      else
+        width = edges[North].border_.Width();
+    }
+    max_intersection_height_ = std::max(max_intersection_height_, height);
+    max_intersection_width_ = std::max(max_intersection_width_, width);
+    intersections_[index] =
+        Intersection(LayoutUnit(width), LayoutUnit(height), winner);
+    // LOG(INFO) << "In: " << row << " " << col << ": " << width << "px " <<
+    // height << "px " << DirectionToStr(winner);
+  }
+}
+
+void TableCollapsedBorderPainter::PopulateEdges(
+    const CellSpan& dirty_rows,
+    const CellSpan& dirty_columns,
+    const TableCollapsedBorderPainter& previous_painter) {
+  VisibleEdgeContainer edges;
+  // Iterate everything in reverse priority order
+  // populate adjacent edges from adjacent section
+  GetVisibleEdgesSiblingSection(edges, previous_painter);
+  MergeVisibleEdges(edges);
+  LayoutTable* table = layout_table_section_->Table();
+  // populate <table>
+  GetVisibleEdgesTable(edges, layout_table_section_->Table());
+  MergeVisibleEdges(edges);
+  // populate <colgroup>
+  Vector<const LayoutTableCol*> colgroups;
+  for (LayoutTableCol* colgroup = table->FirstColumn(); colgroup;
+       colgroup = colgroup->NextColumn())
+    colgroups.push_back(colgroup);
+  for (auto col_group = colgroups.rbegin(); col_group != colgroups.rend();
+       col_group++) {
+    if ((*col_group)->IsTableColumnGroup()) {
+      GetVisibleEdgesColgroup(edges, *col_group);
+      MergeVisibleEdges(edges);
+    }
+  }
+  // populate <col>
+  for (auto col = colgroups.rbegin(); col != colgroups.rend(); col++) {
+    if ((*col)->IsTableColumn()) {
+      GetVisibleEdgesCol(edges, *col);
+      MergeVisibleEdges(edges);
+    }
+  }
+  // populate <tbody>
+  GetVisibleEdgesSection(edges);
+  MergeVisibleEdges(edges);
+  // populate <tr>
+  for (int r = dirty_rows.end() - 1; r >= (int)dirty_rows.Start(); r--) {
+    const LayoutTableRow* row = layout_table_section_->RowLayoutObjectAt(r);
+    if (row) {
+      GetVisibleEdgesRow(edges, row);
+      MergeVisibleEdges(edges);
+    }
+  }
+  // populate <td>, iterate in reverse
+  TextDirection direction = layout_table_section_->Style()->Direction();
+  for (int r = dirty_rows.end() - 1; r >= (int)dirty_rows.Start(); r--) {
+    for (int c = dirty_columns.end() - 1; c >= (int)dirty_columns.Start();
+         c--) {
+      // HashSet for primary cell to eliminate duplicates
+      const LayoutTableCell* cell = layout_table_section_->PrimaryCellAt(r, c);
+      if (cell) {
+        GetVisibleEdgesCell(edges, cell, direction);
+        MergeVisibleEdges(edges);
+      }
+    }
+  }
+  // ShowEdges();
+}
+
+// Gets edges of the neighboring section
+void TableCollapsedBorderPainter::GetVisibleEdgesSiblingSection(
+    VisibleEdgeContainer& edges,
+    const TableCollapsedBorderPainter& previous_painter) {
+  edges.clear();
+  bool is_above =
+      previous_painter.layout_table_section_ ==
+      layout_table_section_->Table()->SectionAbove(layout_table_section_);
+  bool is_below =
+      previous_painter.layout_table_section_ ==
+      layout_table_section_->Table()->SectionBelow(layout_table_section_);
+  if (!is_above && !is_below) {
+    // Happens if we are the first section
+    // LOG(INFO) << "not sure where sibling section is";
+    return;
+  }
+  unsigned siblingRow = is_above ? previous_painter.num_rows_ : 0;
+  unsigned my_row = is_above ? 0 : num_rows_;
+  for (unsigned c = previous_painter.start_visible_column_;
+       c <= previous_painter.end_visible_column_; c++) {
+    auto sibling_index = previous_painter.EdgeToIndex(siblingRow, c, East);
+    auto my_index = EdgeToIndex(my_row, c, East);
+    if (sibling_index != npos && my_index != npos) {
+      EdgeRecord sibling_edge = previous_painter.edges_[sibling_index];
+      edges.push_back(VisibleEdgeRecord(my_row, c, East, sibling_edge.border_,
+                                        sibling_edge.precedence_,
+                                        sibling_edge.resolved_color_));
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::GetVisibleEdgesTable(
+    VisibleEdgeContainer& edges,
+    const LayoutTable* table) {
+  edges.clear();
+  Color resolved_color = table->ResolveColor(CSSPropertyColor);
+  const ComputedStyle* border_style = table->Style();
+  const BorderValue* top_border = &border_style->BorderTop();
+  const BorderValue* right_border = &border_style->BorderRight();
+  const BorderValue* bottom_border = &border_style->BorderBottom();
+  const BorderValue* left_border = &border_style->BorderLeft();
+  RotateBorders(layout_table_section_->Style()->Direction(),
+                table->Style()->GetWritingMode(), &top_border, &right_border,
+                &bottom_border, &left_border);
+  // top row, only if we abut table top
+  if (this->layout_table_section_ == table->TopNonEmptySection()) {
+    FillHorizontalEdges(edges, 0, 0, num_effective_columns_, *top_border,
+                        kBorderPrecedenceTable, resolved_color);
+  }
+  // bottom row, only if we abut table bottom
+  if (this->layout_table_section_ == table->BottomNonEmptySection()) {
+    FillHorizontalEdges(edges, num_rows_, 0, num_effective_columns_,
+                        *bottom_border, kBorderPrecedenceTable, resolved_color);
+  }
+  FillVerticalEdges(edges, 0, 0, num_rows_, *left_border,
+                    kBorderPrecedenceTable, resolved_color);
+  FillVerticalEdges(edges, num_effective_columns_, 0, num_rows_, *right_border,
+                    kBorderPrecedenceTable, resolved_color);
+}
+
+void TableCollapsedBorderPainter::GetVisibleEdgesSection(
+    VisibleEdgeContainer& edges) {
+  edges.clear();
+  Color resolved_color = layout_table_section_->ResolveColor(CSSPropertyColor);
+  // Traverse all the section edges, and assign them
+  FillVisibleRect(edges, 0, 0, num_rows_, num_effective_columns_,
+                  layout_table_section_->Style(), TextDirection::kLtr,
+                  layout_table_section_->Style()->GetWritingMode(),
+                  resolved_color, kBorderPrecedenceRowGroup);
+}
+
+void TableCollapsedBorderPainter::GetVisibleEdgesColgroup(
+    VisibleEdgeContainer& edges,
+    const LayoutTableCol* colgroup) {
+  edges.clear();
+  Color resolved_color = colgroup->ResolveColor(CSSPropertyColor);
+  Vector<unsigned> indexes = colgroup->GetEffectiveColumnIndexes();
+  if (indexes.size() > 0) {
+    unsigned start_col_index = indexes[0];
+    unsigned end_col_index = indexes.back() + 1;
+    FillVisibleRect(edges, 0, start_col_index, num_rows_, end_col_index,
+                    colgroup->Style(), colgroup->Style()->Direction(),
+                    colgroup->Style()->GetWritingMode(), resolved_color,
+                    kBorderPrecedenceColumnGroup);
+  }
+}
+
+void TableCollapsedBorderPainter::GetVisibleEdgesCol(
+    VisibleEdgeContainer& edges,
+    const LayoutTableCol* col) {
+  edges.clear();
+  Color resolved_color = col->ResolveColor(CSSPropertyColor);
+  LayoutTable* table = layout_table_section_->Table();
+  if (!table)
+    return;
+  Vector<unsigned> indexes = col->GetEffectiveColumnIndexes();
+  if (indexes.size() > 0) {
+    // fill multiple virtual columns
+    for (auto idx = indexes.rbegin(); idx != indexes.rend(); ++idx) {
+      FillVisibleRect(edges, 0, *idx, num_rows_, *idx + 1, col->Style(),
+                      col->Style()->Direction(), col->Style()->GetWritingMode(),
+                      resolved_color, kBorderPrecedenceColumn);
+    }
+  }
+  // unsigned startAbsoluteColIndex = table->colElementToAbsoluteColumn(col);
+  // unsigned endAbsoluteColIndex = startAbsoluteColIndex + col->span();
+  // unsigned start_col_index =
+  // table->absolute_columnToEffectiveColumn(startAbsoluteColIndex); unsigned
+  // end_col_index =
+  // table->absolute_columnToEffectiveColumn(endAbsoluteColIndex);
+  // // We replicat column span times. Weird, but that is the standard:
+  // // "For the purposes of the CSS table model, the col element is expected to
+  // be treated as if it was present as many times as its span attribute
+  // specifies." for (auto tmpEnd = end_col_index; tmpEnd > start_col_index;
+  // tmpEnd--) {
+  //     FillVisibleRect(edges, 0, tmpEnd - 1, num_rows_, tmpEnd, col->Style(),
+  //         col->Style()->Direction(), col->Style()->GetWritingMode(),
+  //         resolved_color, BorderPrecedenceColumn);
+  // }
+}
+
+void TableCollapsedBorderPainter::GetVisibleEdgesRow(
+    VisibleEdgeContainer& edges,
+    const LayoutTableRow* row) {
+  edges.clear();
+  Color resolved_color = row->ResolveColor(CSSPropertyColor);
+  unsigned rowIndex = row->RowIndex();
+  // We get direction from section because row direction only applies to cells,
+  // not the entire row.
+  FillVisibleRect(edges, rowIndex, 0, rowIndex + 1, num_effective_columns_,
+                  row->Style(), layout_table_section_->Style()->Direction(),
+                  row->Style()->GetWritingMode(), resolved_color,
+                  kBorderPrecedenceRow);
+}
+
+void TableCollapsedBorderPainter::GetVisibleEdgesCell(
+    VisibleEdgeContainer& edges,
+    const LayoutTableCell* cell,
+    TextDirection direction) {
+  edges.clear();
+  Color resolved_color = cell->ResolveColor(CSSPropertyColor);
+  if (!cell->Parent()) {
+    LOG(INFO) << "DETACHED CELL";
+    return;
+  }
+  const LayoutTable* table = layout_table_section_->Table();
+  unsigned start_row = cell->Parent() ? cell->RowIndex() : 65000;
+  unsigned absolute_col = cell->AbsoluteColumnIndex();
+  unsigned eff_start_col = table->AbsoluteColumnToEffectiveColumn(absolute_col);
+  unsigned eff_end_col =
+      table->AbsoluteColumnToEffectiveColumn(absolute_col + cell->ColSpan());
+  unsigned end_row = std::min(start_row + cell->RowSpan(), num_rows_);
+  // LOG(INFO) << "m_columns: " << table->effective_columns().size()
+  //      << " start_row: " << start_row << " end_row: " << end_row
+  //      << " startCol: " << eff_start_col << " endCol:" << eff_end_col
+  //      << " abscol:" << absolute_col;
+  // Fill border
+  // cell's direction is LTR because we do not rotate cell's borders
+  FillVisibleRect(edges, start_row, eff_start_col, end_row, eff_end_col,
+                  cell->Style(), direction, cell->Style()->GetWritingMode(),
+                  resolved_color, kBorderPrecedenceCell);
+  // Hide row inner edges
+  for (unsigned row = start_row + 1; row < end_row; row++) {
+    if (row >= start_visible_row_ && row < end_visible_row_) {
+      for (unsigned effCol = eff_start_col; effCol < eff_end_col; effCol++) {
+        if (effCol >= start_visible_column_ && effCol < end_visible_column_) {
+          edges.push_back(VisibleEdgeRecord(row, effCol, East, hidden_border_,
+                                            kBorderPrecedenceCell,
+                                            resolved_color, true));
+        }
+      }
+    }
+  }
+  // Hide col inner edges
+  for (unsigned effCol = eff_start_col + 1; effCol < eff_end_col; effCol++) {
+    if (effCol >= start_visible_column_ && effCol < end_visible_column_) {
+      for (unsigned row = start_row; row < end_row; row++) {
+        if (row >= start_visible_row_ && row < end_visible_row_) {
+          edges.push_back(VisibleEdgeRecord(row, effCol, South, hidden_border_,
+                                            kBorderPrecedenceCell,
+                                            resolved_color, true));
+        }
+      }
+    }
+  }
+  // ShowVisibleEdges(edges);
+}
+
+void TableCollapsedBorderPainter::RotateBorders(
+    TextDirection text_direction,
+    WritingMode writing_mode,
+    const BorderValue** top,
+    const BorderValue** right,
+    const BorderValue** bottom,
+    const BorderValue** left) const {
+  bool is_ltr = blink::IsLeftToRightDirection(text_direction);
+  if (blink::IsHorizontalWritingMode(writing_mode)) {
+    if (is_ltr) {
+    }  // do nothing
+    else {
+      std::swap(*right, *left);
+    }
+  } else if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+    if (is_ltr) {
+      auto tmp = *top;
+      *top = *right;
+      *right = *bottom;
+      *bottom = *left;
+      *left = tmp;
+    } else {
+      std::swap(*top, *right);
+      std::swap(*bottom, *left);
+    }
+  } else {  // IsFlippedLinesWritingMode
+    if (is_ltr) {
+      std::swap(*bottom, *right);
+      std::swap(*left, *top);
+    } else {
+      auto tmp = *top;
+      *top = *left;
+      *left = *bottom;
+      *bottom = *right;
+      *right = tmp;
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::FillVisibleRect(
+    VisibleEdgeContainer& edges,
+    unsigned start_row,
+    unsigned start_column,
+    unsigned end_row,
+    unsigned end_column,
+    const ComputedStyle* border_style,
+    TextDirection text_direction,
+    WritingMode writing_mode,
+    Color resolved_color,
+    EBorderPrecedence precedence) {
+  const BorderValue* top_border = &border_style->BorderTop();
+  const BorderValue* bottom_border = &border_style->BorderBottom();
+  const BorderValue* right_border = &border_style->BorderRight();
+  const BorderValue* left_border = &border_style->BorderLeft();
+  RotateBorders(text_direction, writing_mode, &top_border, &right_border,
+                &bottom_border, &left_border);
+  FillHorizontalEdges(edges, start_row, start_column, end_column, *top_border,
+                      precedence, resolved_color);
+  FillHorizontalEdges(edges, end_row, start_column, end_column, *bottom_border,
+                      precedence, resolved_color);
+  FillVerticalEdges(edges, start_column, start_row, end_row, *left_border,
+                    precedence, resolved_color);
+  FillVerticalEdges(edges, end_column, start_row, end_row, *right_border,
+                    precedence, resolved_color);
+}
+
+void TableCollapsedBorderPainter::FillHorizontalEdges(
+    VisibleEdgeContainer& edges,
+    unsigned row,
+    unsigned start_column,
+    unsigned end_column,
+    const BorderValue& border,
+    EBorderPrecedence precedence,
+    Color resolved_color) {
+  if (border.Style() == kBorderStyleNone)
+    return;
+  if (row >= start_visible_row_ && row < end_visible_row_) {
+    for (unsigned c = start_column; c < end_column; c++) {
+      // FIXME: modify for loop instead of comparing guard
+      if (c >= start_visible_column_ && c < end_visible_column_) {
+        edges.push_back(VisibleEdgeRecord(row, c, East, border, precedence,
+                                          resolved_color));
+      }
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::FillVerticalEdges(
+    VisibleEdgeContainer& edges,
+    unsigned column,
+    unsigned start_row,
+    unsigned end_row,
+    const BorderValue& border,
+    EBorderPrecedence precedence,
+    Color resolved_color) {
+  if (border.Style() == kBorderStyleNone)
+    return;
+  if (column >= start_visible_column_ && column < end_visible_column_) {
+    for (unsigned r = start_row; r < end_row; r++) {
+      // FIXME: modify for loop instead of comparing guard
+      if (r >= start_visible_row_ && r < end_visible_row_) {
+        edges.push_back(VisibleEdgeRecord(r, column, South, border, precedence,
+                                          resolved_color));
+      }
+    }
+  }
+}
+
+void TableCollapsedBorderPainter::MergeVisibleEdges(
+    VisibleEdgeContainer& edges) {
+  for (auto edge = edges.begin(); edge < edges.end(); edge++) {
+    unsigned idx =
+        EdgeToIndex((*edge).m_row, (*edge).m_column, (*edge).direction_);
+    DCHECK(idx != npos);
+    EdgeRecord edge_record((*edge).border_, (*edge).precedence_,
+                           (*edge).resolved_color_);
+    if ((*edge).force_removal_)
+      edges_[idx] = edge_record;
+    // if both edges are same priority, new edge wins
+    if (CompareEdges(edges_[idx], edge_record) != 1)
+      edges_[idx] = edge_record;
+  }
+}
+
+static EBorderStyle CollapsedBorderStyle(EBorderStyle style) {
+  if (style == kBorderStyleOutset)
+    return kBorderStyleGroove;
+  if (style == kBorderStyleInset)
+    return kBorderStyleRidge;
+  return style;
+}
+
+void TableCollapsedBorderPainter::PaintEdges(const PaintInfo& paint_info,
+                                             const LayoutPoint& paint_offset,
+                                             const CellSpan& rows,
+                                             const CellSpan& cols) {
+  // see TableCellPainter::paintCollapsedBorders
+  LayoutRect paint_rect = layout_table_section_->GetCellPhysicalPosition(
+      rows.Start(), cols.Start());
+  paint_rect.Unite(layout_table_section_->GetCellPhysicalPosition(
+      rows.end() > 0 ? rows.end() - 1 : 0,
+      cols.end() > 0 ? cols.end() - 1 : 0));
+  // paint_rect size calculation is not exact, we expand by maxborder, instead
+  // of exact border
+  paint_rect.Expand(LayoutSize(LayoutUnit(max_intersection_width_ * 2),
+                               LayoutUnit(max_intersection_height_ * 2)));
+  paint_rect.MoveBy(paint_offset);
+  LayoutPoint location = layout_table_section_->Location();
+  paint_rect.MoveBy(location);
+  if (LayoutObjectDrawingRecorder::UseCachedDrawingIfPossible(
+          paint_info.context, *layout_table_section_,
+          DisplayItem::kTableCollapsedBorderBase))
+    return;
+  LayoutObjectDrawingRecorder recorder(
+      paint_info.context, *layout_table_section_,
+      DisplayItem::kTableCollapsedBorderBase, paint_rect);
+  // Paint edges carefully to get them all
+  // Every row paint    : ┌┌┌┌┌, then |
+  // Bottom border paint: _____
+  WritingMode writing_mode = layout_table_section_->Style()->GetWritingMode();
+  TextDirection text_direction = layout_table_section_->Style()->Direction();
+  for (unsigned r = rows.Start(); r < rows.end(); r++) {
+    // const LayoutTableRow * row = layout_table_section_->rowLayoutObjectAt(r);
+    // if (row)
+    //     text_direction = row->Style()->Direction();
+    for (unsigned c = cols.Start(); c < cols.end(); c++) {
+      PaintOneEdge(paint_info, paint_offset, r, c, East, writing_mode,
+                   text_direction);
+      PaintOneEdge(paint_info, paint_offset, r, c, South, writing_mode,
+                   text_direction);
+    }
+    // paint the last column on edge
+    PaintOneEdge(paint_info, paint_offset, r, cols.end(), South, writing_mode,
+                 text_direction);
+  }
+  // Paint the last row
+  for (unsigned c = cols.Start(); c < cols.end(); c++) {
+    PaintOneEdge(paint_info, paint_offset, rows.end(), c, East, writing_mode,
+                 text_direction);
+  }
+}
+
+// Returns a rect that encloses 'direction' border of the cell_rect
+LayoutRect TableCollapsedBorderPainter::CellRectAsBorder(
+    const LayoutRect& cell_rect,
+    BoxSide side,
+    unsigned border_width,
+    WritingMode writing_mode,
+    TextDirection text_direction) {
+  LayoutUnit small_half(border_width / 2);  // C++ always rounds down
+  // unsigned bigHalf = border_width - small_half;
+  LayoutUnit top_offset;
+  LayoutUnit left_offset;
+  /* Tricky: if the border width is odd, we need a consistent way of
+   *      distributing the extra pixel. The rule is:
+   *           - south and east edges always get the extra pixel on the inside
+   *                  of the cell
+   *                       */
+  bool is_ltr = blink::IsLeftToRightDirection(text_direction);
+  if (blink::IsHorizontalWritingMode(writing_mode)) {
+    if (is_ltr) {
+      top_offset = small_half;
+      left_offset = small_half;
+    } else {
+      top_offset = small_half;
+      left_offset = small_half;
+    }
+  } else {  // vertical
+    if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+      if (is_ltr) {
+        top_offset = small_half;
+        left_offset = small_half;
+      } else {
+        top_offset = small_half;
+        left_offset = small_half;
+      }
+    } else {  // flippedLines
+      if (is_ltr) {
+        top_offset = small_half;
+        left_offset = small_half;
+      } else {
+        top_offset = small_half;
+        left_offset = small_half;
+      }
+    }
+  }
+  switch (side) {
+    case kBSTop:
+      return LayoutRect(
+          LayoutPoint(cell_rect.X(), cell_rect.Y() - top_offset),
+          LayoutSize(cell_rect.Width(), LayoutUnit(border_width)));
+    case kBSBottom:
+      return LayoutRect(
+          LayoutPoint(cell_rect.X(), cell_rect.MaxY() - top_offset),
+          LayoutSize(cell_rect.Width(), LayoutUnit(border_width)));
+    case kBSLeft:
+      return LayoutRect(
+          LayoutPoint(cell_rect.X() - left_offset, cell_rect.Y()),
+          LayoutSize(LayoutUnit(border_width), cell_rect.Height()));
+    case kBSRight:
+      return LayoutRect(
+          LayoutPoint(cell_rect.MaxX() - left_offset, cell_rect.Y()),
+          LayoutSize(LayoutUnit(border_width), cell_rect.Height()));
+  }
+}
+
+//
+LayoutRect TableCollapsedBorderPainter::EdgePaintPosition(
+    unsigned row,
+    unsigned col,
+    unsigned border_width,
+    EdgeDirection direction,
+    WritingMode writing_mode,
+    TextDirection text_direction) {
+  // Compute edge's size from size of the cell
+  LayoutRect position;
+  bool is_ltr = blink::IsLeftToRightDirection(text_direction);
+  BoxSide side = kBSLeft;
+  LayoutRect cell_rect;
+  // If this is the last row intersection, get size from cell in next to last
+  if (row == num_rows_) {
+    DCHECK(direction == East);
+    cell_rect = GetCellPhysicalPosition(row - 1, col);
+    if (blink::IsHorizontalWritingMode(writing_mode)) {
+      side = kBSBottom;
+    } else if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+      side = kBSLeft;
+    } else {
+      side = kBSRight;
+    }
+  } else if (col == num_effective_columns_) {
+    // If this is the last column, get size from the cell before
+    DCHECK(direction == South);
+    cell_rect = GetCellPhysicalPosition(row, col - 1);
+    if (blink::IsHorizontalWritingMode(writing_mode)) {
+      side = is_ltr ? kBSRight : kBSLeft;
+    } else if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+      side = is_ltr ? kBSBottom : kBSTop;
+    } else {
+      side = is_ltr ? kBSBottom : kBSTop;
+    }
+  } else {
+    cell_rect = GetCellPhysicalPosition(row, col);
+    if (direction == East) {
+      if (blink::IsHorizontalWritingMode(writing_mode)) {
+        side = kBSTop;
+      } else if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+        side = kBSRight;
+      } else {
+        side = kBSLeft;
+      }
+    } else {  // direction == South
+      if (blink::IsHorizontalWritingMode(writing_mode)) {
+        side = is_ltr ? kBSLeft : kBSRight;
+      } else if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+        side = is_ltr ? kBSTop : kBSBottom;
+      } else {  // flippedLines
+        side = is_ltr ? kBSTop : kBSBottom;
+      }
+    }
+  }
+  return CellRectAsBorder(cell_rect, side, border_width, writing_mode,
+                          text_direction);
+}
+
+// Paints an edge starting from intersection[row, col] in direction
+void TableCollapsedBorderPainter::PaintOneEdge(const PaintInfo& paint_info,
+                                               const LayoutPoint& paint_offset,
+                                               unsigned row,
+                                               unsigned col,
+                                               EdgeDirection direction,
+                                               WritingMode writing_mode,
+                                               TextDirection text_direction) {
+  DCHECK(direction == South || direction == East);
+  unsigned idx = EdgeToIndex(row, col, direction);
+  DCHECK(idx != npos);
+  const BorderValue& border = edges_[idx].border_;
+  if (border.Style() == kBorderStyleHidden || !border.NonZero())
+    return;
+  LayoutTableSection* section_above =
+      layout_table_section_->Table()->SectionAbove(layout_table_section_,
+                                                   kSkipEmptySections);
+  if (!row && direction == East && section_above) {
+    return;
+  }
+  // EdgeRecord edge = edges_[idx];
+  // ShowEdge(row, col, direction, edge.precedence_, edge.border_,
+  //    border.Color().Resolve(edges_[idx].resolved_color_));
+  LayoutRect position = EdgePaintPosition(row, col, border.Width(), direction,
+                                          writing_mode, text_direction);
+  AdjustForIntersections(position, row, col, direction, writing_mode,
+                         text_direction);
+  // Offset by section_location
+  LayoutPoint section_location = layout_table_section_->Location();
+  position.MoveBy(section_location);
+  position.MoveBy(paint_offset);
+  BoxSide side;
+  if (blink::IsHorizontalWritingMode(writing_mode))
+    side = direction == East ? kBSTop : kBSLeft;
+  else
+    side = direction == East ? kBSLeft : kBSTop;
+  ObjectPainter::DrawLineForBoxSide(
+      paint_info.context, position.X(), position.Y(), position.MaxX(),
+      position.MaxY(),  // left, top, right, bottom,
+      side, border.GetColor().Resolve(edges_[idx].resolved_color_),
+      CollapsedBorderStyle(border.Style()), 0, 0, true);
+}
+
+void TableCollapsedBorderPainter::AdjustForIntersections(
+    LayoutRect& position,
+    unsigned row,
+    unsigned col,
+    EdgeDirection direction,
+    WritingMode writing_mode,
+    TextDirection text_direction) {
+  DCHECK(direction == South || direction == East);
+  const Intersection* start_intersection = nullptr;
+  const Intersection* end_intersection = nullptr;
+  bool winner_start = false;
+  bool winner_end = false;
+  // START intersection
+  unsigned index = IntersectionToIndex(row, col);
+  if (index != npos) {
+    start_intersection = &intersections_[index];
+    winner_start = start_intersection->direction_ == direction;
+  }
+  // END intersection
+  if (direction == South)
+    row += 1;
+  else
+    col += 1;
+  index = IntersectionToIndex(row, col);
+  if (index != npos) {
+    end_intersection = &intersections_[index];
+    if (direction == South)
+      winner_end = end_intersection->direction_ == North;
+    else
+      winner_end = end_intersection->direction_ == West;
+  }
+  bool is_ltr = blink::IsLeftToRightDirection(text_direction);
+  if (blink::IsHorizontalWritingMode(writing_mode)) {
+    AdjustForIntersectionsHorizontal(position, direction, is_ltr,
+                                     start_intersection, winner_start,
+                                     end_intersection, winner_end);
+  } else if (blink::IsFlippedBlocksWritingMode(writing_mode)) {
+    AdjustForIntersectionsFlippedBlocks(position, direction, is_ltr,
+                                        start_intersection, winner_start,
+                                        end_intersection, winner_end);
+  } else if (blink::IsFlippedLinesWritingMode(writing_mode)) {
+    AdjustForIntersectionsFlippedLines(position, direction, is_ltr,
+                                       start_intersection, winner_start,
+                                       end_intersection, winner_end);
+  } else {
+    DCHECK(false);
+  }
+}
+
+/*
+ * writing-mode: HORIZONTAL-TB
+ *             N
+ *             compass: W--+--E  intersection:   <--width -->
+ *                         S
+ *                             start intersection
+ *                                   South edge, win : expand top by height/2
+ *                                         South edge, lose: shrink top by
+ * height/2 East edge, win  : expand left by width/2 East edge, lose : shrink
+ * left by width/2 end
+ * intersection South
+ * edge, win :
+ * expand bottom by height/2 South edge lose : shrink bottom by height/2 East
+ * edge, win  : expand right by width/2 East edge, lose : shrink right
+ * by
+ * width/2 writing-mode: HORIZONTAL(RTL)
+ *                                                                                             N
+ *                                                                                             compass:
+ * E--+--W     intersection: <-- width -->
+ *                                                                                                         S
+ *                                                                                                         same
+ * as HORIZONTAL-TB in South direction start intersection South: same as LTR
+ *                                                                                                                             East
+ * edge, win  : expand right by width/2 East
+ * edge, lose : shrink right by
+ * width/2 end intersection South: same as LTR East
+ * edge, win  : expand left by width/2 East edge, lose : shrink left by width/2
+ *                                                                                                                                                                 */
+void TableCollapsedBorderPainter::AdjustForIntersectionsHorizontal(
+    LayoutRect& position,
+    EdgeDirection direction,
+    bool is_ltr,
+    const Intersection* start_intersection,
+    bool winner_start,
+    const Intersection* end_intersection,
+    bool winner_end) {
+  if (start_intersection) {
+    if (direction == South) {
+      unsigned small_delta = start_intersection->height_.ToUnsigned() / 2;
+      unsigned big_delta =
+          start_intersection->height_.ToUnsigned() - small_delta;
+      if (winner_start) {
+        position.ExpandEdges(LayoutUnit(small_delta), LayoutUnit(0),
+                             LayoutUnit(0), LayoutUnit(0));
+      } else {
+        position.ContractEdges(LayoutUnit(big_delta), LayoutUnit(0),
+                               LayoutUnit(0), LayoutUnit(0));
+      }
+    } else {  // East
+      unsigned small_delta = start_intersection->width_.ToUnsigned() / 2;
+      unsigned big_delta =
+          start_intersection->width_.ToUnsigned() - small_delta;
+      if (is_ltr) {
+        if (winner_start) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(small_delta));
+        } else {
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                                 LayoutUnit(big_delta));
+        }
+      } else {  // RTL
+        if (winner_start) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(small_delta),
+                               LayoutUnit(0), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(big_delta),
+                                 LayoutUnit(0), LayoutUnit(0));
+        }
+      }
+    }
+  }
+  if (end_intersection) {
+    if (direction == South) {
+      unsigned small_delta = end_intersection->height_.ToUnsigned() / 2;
+      unsigned big_delta = end_intersection->height_.ToUnsigned() - small_delta;
+      if (winner_end) {
+        position.ExpandEdges(LayoutUnit(0), LayoutUnit(0),
+                             LayoutUnit(big_delta), LayoutUnit(0));
+      } else {
+        position.ContractEdges(LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(small_delta), LayoutUnit(0));
+      }
+    } else {  // East
+      unsigned small_delta = end_intersection->width_.ToUnsigned() / 2;
+      unsigned big_delta = end_intersection->width_.ToUnsigned() - small_delta;
+      if (is_ltr) {
+        if (winner_end) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(big_delta),
+                               LayoutUnit(0), LayoutUnit(0));
+        } else {  // loser
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(small_delta),
+                                 LayoutUnit(0), LayoutUnit(0));
+        }
+      } else {  // RTL
+        if (winner_end) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(big_delta));
+        } else {
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                                 LayoutUnit(small_delta));
+        }
+      }
+    }
+  }
+}
+
+/*
+ * writing-mode: VERTICAL-RL (flipped blocks)
+ *                       W
+ *                       compass: vertical: S--+--N  intersection: <--- height
+ * ---->
+ *                                             E
+ *                                                 start intersection
+ *                                                       South edge, win :
+ * expand right by height/2 South edge, lose: shrink right by height/2 East
+ * edge, win
+ * : expand top by width/2 East edge, lose : shrink top by width/2 end
+ * intersection South edge, win : expand left by height/2 South
+ * edge, lose:
+ * shrink left by height/2 East edge, win  :
+ * expand bottom by
+ * width/2 East edge, lose : shrink bottom by width/2
+ *                                                                                                     writing-mode:
+ * VERTICAL-RL RTL
+ *                                                                                                                           E
+ *                                                                                                                           compass:
+ * vertical: S--+--N  intersection: <--- height ---->
+ *                                                                                                                                                 W
+ *                                                                                                                                                     start
+ * intersection South edge, win : expand right by height/2 South
+ * edge, lose:
+ * shrink right by height/2 East
+ * edge, win  : expand bottom by
+ * width/2 East
+ * edge, lose : shrink bottom by
+ * width/2 end intersection South
+ * edge, win :
+ * expand left by height/2 South edge, lose: shrink left by height/2
+ *                                                                                                                                                                                                   East
+ * edge, win  : expand top by width/2 East edge, lose : shrink top by width/2
+ *                                                                                                                                                                                                         */
+void TableCollapsedBorderPainter::AdjustForIntersectionsFlippedBlocks(
+    LayoutRect& position,
+    EdgeDirection direction,
+    bool is_ltr,
+    const Intersection* start_intersection,
+    bool winner_start,
+    const Intersection* end_intersection,
+    bool winner_end) {
+  if (start_intersection) {
+    if (direction == South) {
+      unsigned small_delta = start_intersection->height_.ToUnsigned() / 2;
+      unsigned big_delta =
+          start_intersection->height_.ToUnsigned() - small_delta;
+      if (winner_start) {
+        position.ExpandEdges(LayoutUnit(0), LayoutUnit(small_delta),
+                             LayoutUnit(0), LayoutUnit(0));
+      } else {
+        position.ContractEdges(LayoutUnit(0), LayoutUnit(big_delta),
+                               LayoutUnit(0), LayoutUnit(0));
+      }
+    } else {  // East
+      unsigned small_delta = start_intersection->width_.ToUnsigned() / 2;
+      unsigned big_delta =
+          start_intersection->width_.ToUnsigned() - small_delta;
+      if (is_ltr) {
+        if (winner_start) {
+          position.ExpandEdges(LayoutUnit(small_delta), LayoutUnit(0),
+                               LayoutUnit(0), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(big_delta), LayoutUnit(0),
+                                 LayoutUnit(0), LayoutUnit(0));
+        }
+      } else {  // RTL
+        if (winner_start) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(big_delta), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(0),
+                                 LayoutUnit(small_delta), LayoutUnit(0));
+        }
+      }
+    }
+  }
+  if (end_intersection) {
+    if (direction == South) {
+      unsigned small_delta = end_intersection->height_.ToUnsigned() / 2;
+      unsigned big_delta = end_intersection->height_.ToUnsigned() - small_delta;
+      if (winner_end) {
+        position.ExpandEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                             LayoutUnit(big_delta));
+      } else {
+        position.ContractEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(small_delta));
+      }
+    } else {  // East
+      unsigned small_delta = end_intersection->width_.ToUnsigned() / 2;
+      unsigned big_delta = end_intersection->width_.ToUnsigned() - small_delta;
+      if (is_ltr) {
+        if (winner_end) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(big_delta), LayoutUnit(0));
+        } else {  // loser
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(0),
+                                 LayoutUnit(small_delta), LayoutUnit(0));
+        }
+      } else {  // RTL
+        if (winner_end) {
+          position.ExpandEdges(LayoutUnit(big_delta), LayoutUnit(0),
+                               LayoutUnit(0), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(small_delta), LayoutUnit(0),
+                                 LayoutUnit(0), LayoutUnit(0));
+        }
+      }
+    }
+  }
+}
+
+/*
+ * writing-mode: VERTICAL-LR (flipped lines)
+ *                     W
+ *                     compass: rotated N--+--S
+ *                                         E
+ *                                             start intersection
+ *                                                     East edge, win  : expand
+ * top by width/2 East edge, lose : shrink top by width/2 South edge, win :
+ * expand
+ * left by height/2 South edge, lose: shrink left by height/2 end intersection
+ *                                                                                         East
+ * edge, win  : expand bottom by width/2 East edge, lose
+ * : shrink bottom by
+ * width/2 South edge, win : expand right by height/2 South
+ * edge lose : shrink right by height/2 writing-mode: VERTICAL-LR, DIRECTION RTL
+ *                                                                                                                            E
+ *                                                                                                                            compass:
+ * N-+-S     intersection <--height -->
+ *                                                                                                                                       W
+ *                                                                                                                                           start
+ * intersection East edge. win : expand bottom by width / 2 East
+ * edge, lose:
+ * shrink bottom by width / 2 end intersection East
+ * edge, win :
+ * expand top by width / 2 East edge, lose: expand top by width / 2
+ *                                                                                                                                                                               */
+void TableCollapsedBorderPainter::AdjustForIntersectionsFlippedLines(
+    LayoutRect& position,
+    EdgeDirection direction,
+    bool is_ltr,
+    const Intersection* start_intersection,
+    bool winner_start,
+    const Intersection* end_intersection,
+    bool winner_end) {
+  if (start_intersection) {
+    if (direction == South) {
+      unsigned small_delta = start_intersection->height_.ToUnsigned() / 2;
+      unsigned big_delta =
+          start_intersection->height_.ToUnsigned() - small_delta;
+      if (winner_start) {
+        position.ExpandEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                             LayoutUnit(small_delta));
+      } else {
+        position.ContractEdges(LayoutUnit(0), LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(big_delta));
+      }
+    } else {  // East
+      unsigned small_delta = start_intersection->width_.ToUnsigned() / 2;
+      unsigned big_delta =
+          start_intersection->width_.ToUnsigned() - small_delta;
+      if (is_ltr) {
+        if (winner_start) {
+          position.ExpandEdges(LayoutUnit(small_delta), LayoutUnit(0),
+                               LayoutUnit(0), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(big_delta), LayoutUnit(0),
+                                 LayoutUnit(0), LayoutUnit(0));
+        }
+      } else {  // RTL
+        if (winner_start) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(small_delta), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(0),
+                                 LayoutUnit(big_delta), LayoutUnit(0));
+        }
+      }
+    }
+  }
+  if (end_intersection) {
+    if (direction == South) {
+      unsigned small_delta = end_intersection->height_.ToUnsigned() / 2;
+      unsigned big_delta = end_intersection->height_.ToUnsigned() - small_delta;
+      if (winner_end) {
+        position.ExpandEdges(LayoutUnit(0), LayoutUnit(big_delta),
+                             LayoutUnit(0), LayoutUnit(0));
+      } else {
+        position.ContractEdges(LayoutUnit(0), LayoutUnit(small_delta),
+                               LayoutUnit(0), LayoutUnit(0));
+      }
+    } else {  // East
+      unsigned small_delta = end_intersection->width_.ToUnsigned() / 2;
+      unsigned big_delta = end_intersection->width_.ToUnsigned() - small_delta;
+      if (is_ltr) {
+        if (winner_end) {
+          position.ExpandEdges(LayoutUnit(0), LayoutUnit(0),
+                               LayoutUnit(big_delta), LayoutUnit(0));
+        } else {  // loser
+          position.ContractEdges(LayoutUnit(0), LayoutUnit(0),
+                                 LayoutUnit(small_delta), LayoutUnit(0));
+        }
+      } else {  // RTL
+        if (winner_end) {
+          position.ExpandEdges(LayoutUnit(big_delta), LayoutUnit(0),
+                               LayoutUnit(0), LayoutUnit(0));
+        } else {
+          position.ContractEdges(LayoutUnit(small_delta), LayoutUnit(0),
+                                 LayoutUnit(0), LayoutUnit(0));
+        }
+      }
+    }
+  }
+}
+
+// returns edge index for position, TableCollapsedBorderPainter::npos if out of
+// range topLeft intersection is 0, 0, bottomRight is numRows+1, numColumns + 1
+unsigned TableCollapsedBorderPainter::EdgeToIndex(
+    unsigned intersection_row,
+    unsigned intersection_column,
+    EdgeDirection direction) const {
+  /*  Edges map to edges_ like this:
+   *      - each intersection 'stores' only two edges: east and south edges
+   *          - to map edge to index:
+   *                - find intersection so that requested edge is east or south
+   *                      - edge is row * cols * 2 + (east ? 0 : 1)
+   *                          - for example:
+   *                                - North edge at intersection 5, 3, is also
+   * South edge at intersection 4, 3 - its index is 4 (rows) * 3 (cols) * 2 + 1
+   * (for South)
+   *                                      */
+  switch (direction) {
+    case North:
+      intersection_row -= 1;
+      direction = South;
+      break;
+    case West:
+      intersection_column -= 1;
+      direction = East;
+      break;
+    case South:
+    case East:
+    case None:
+      break;
+  }
+  // Check if we are inside the covered area
+  if (intersection_row < start_visible_row_ ||
+      intersection_column < start_visible_column_ ||
+      intersection_row >= end_visible_row_ ||
+      intersection_column >= end_visible_column_) {
+    // LOG(ERROR) << "GOT AN NPOS";
+    return TableCollapsedBorderPainter::npos;
+  }
+  unsigned index = (intersection_row - start_visible_row_) *
+                   (end_visible_column_ - start_visible_column_) * 2;
+  index += (intersection_column - start_visible_column_) * 2;
+  return direction == East ? index
+                           : index + 1;  // each vertex holds [East, South]
+}
+
+unsigned TableCollapsedBorderPainter::IntersectionToIndex(
+    unsigned row,
+    unsigned column) const {
+  if (row < start_visible_row_ || column < start_visible_column_ ||
+      row >= end_visible_row_ || column >= end_visible_column_)
+    return TableCollapsedBorderPainter::npos;
+  return (row - start_visible_row_) *
+             (end_visible_column_ - start_visible_column_) +
+         column;
+}
+}
+// blink