Update our treatment of repeating headers in tables

third_party/WebKit/Source/core/layout/LayoutTableSection.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009, 2010, 2013 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
@@ skipping 79 matching lines @@
     : LayoutTableBoxComponent(element),
       c_col_(0),
       c_row_(0),
       outer_border_start_(0),
       outer_border_end_(0),
       outer_border_before_(0),
       outer_border_after_(0),
       needs_cell_recalc_(false),
       force_full_paint_(false),
       has_multiple_cell_levels_(false),
-      has_spanning_cells_(false) {
+      has_spanning_cells_(false),
+      is_repeating_header_group_(false) {
   // init LayoutObject attributes
   SetInline(false);  // our object is not Inline
 }
 
 LayoutTableSection::~LayoutTableSection() {}
 
 void LayoutTableSection::StyleDidChange(StyleDifference diff,
                                         const ComputedStyle* old_style) {
   DCHECK(Style()->Display() == EDisplay::kTableFooterGroup ||
          Style()->Display() == EDisplay::kTableRowGroup ||
@@ skipping 1928 matching lines @@
     }
 
     if (!row_is_at_top_of_column)
       return;
   }
   // We need to push this row to the next fragmentainer. If there are repeated
   // table headers, we need to make room for those at the top of the next
   // fragmentainer, above this row. Otherwise, this row will just go at the top
   // of the next fragmentainer.
 
-  LayoutTableSection* header = Table()->Header();
-  if (row_object.IsFirstRowInSectionAfterHeader())
-    Table()->SetRowOffsetFromRepeatingHeader(LayoutUnit());
   // Border spacing from the previous row has pushed this row just past the top
   // of the page, so we must reposition it to the top of the page and avoid any
   // repeating header.
   if (row_is_at_top_of_column && offset_from_top_of_page)
     pagination_strut -= offset_from_top_of_page.ToInt();
 
   // If we have a header group we will paint it at the top of each page,
   // move the rows down to accomodate it.
+  LayoutTableSection* header = Table()->Header();
   if (header && header != this)
     pagination_strut += Table()->RowOffsetFromRepeatingHeader().ToInt();
   row_object.SetPaginationStrut(LayoutUnit(pagination_strut));
 
   // We have inserted a pagination strut before the row. Adjust the logical top
   // and re-lay out. We no longer want to break inside the row, but rather
   // *before* it. From the previous layout pass, there are most likely
   // pagination struts inside some cell in this row that we need to get rid of.
   row_object.SetLogicalTop(row_object.LogicalTop() + pagination_strut);
   layouter.SetChildNeedsLayout(&row_object);
   row_object.LayoutIfNeeded();
 
   // It's very likely that re-laying out (and nuking pagination struts inside
   // cells) gave us a new height.
   row_object.SetLogicalHeight(LayoutUnit(LogicalHeightForRow(row_object)));
 }
 
-bool LayoutTableSection::IsRepeatingHeaderGroup() const {
-  if (GetPaginationBreakability() == LayoutBox::kAllowAnyBreaks)
+bool LayoutTableSection::HeaderGroupShouldRepeat() const {
+  if (Table()->Header() != this)
     return false;
-  // TODO(rhogan): Should we paint a header repeatedly if it's self-painting?
+
+  if (GetPaginationBreakability() == kAllowAnyBreaks)
+    return false;
+  // TODO(rhogan): Sections can be self-painting.
   if (HasSelfPaintingLayer())
     return false;
-  LayoutUnit page_height = Table()->PageLogicalHeightForOffset(LayoutUnit());
+  LayoutUnit page_height = PageLogicalHeightForOffset(LayoutUnit());
+  // If we don't know the page height yet, just assume we fit.
   if (!page_height)
-    return false;
+    return true;
 
   if (LogicalHeight() > page_height)
     return false;
 
-  // If the first row of the section after the header group doesn't fit on the
-  // page, then don't repeat the header on each page.
-  // See https://drafts.csswg.org/css-tables-3/#repeated-headers
-  LayoutTableSection* section_below = Table()->SectionBelow(this);
-  if (!section_below)
-    return true;
-  if (LayoutTableRow* first_row = section_below->FirstRow()) {
-    if (first_row->PaginationStrut() ||
-        first_row->LogicalHeight() > page_height)
-      return false;
-  }
+  // See https://drafts.csswg.org/css-tables-3/#repeated-headers which says
+  // a header/footer can repeat if it takes up less than a quarter of the page.
+  if (LogicalHeight() > 0 && page_height / LogicalHeight() < 4)
+    return false;
 
   return true;
 }
 
 bool LayoutTableSection::MapToVisualRectInAncestorSpaceInternal(
     const LayoutBoxModelObject* ancestor,
     TransformState& transform_state,
     VisualRectFlags flags) const {
   if (ancestor == this)
     return true;
   // Repeating table headers are painted once per fragmentation page/column.
   // This does not go through the regular fragmentation machinery, so we need
   // special code to expand the invalidation rect to contain all positions of
   // the header in all columns.
   // Note that this is in flow thread coordinates, not visual coordinates. The
   // enclosing LayoutFlowThread will convert to visual coordinates.
-  if (Table()->Header() == this && IsRepeatingHeaderGroup()) {
+  if (IsRepeatingHeaderGroup()) {
     transform_state.Flatten();
     FloatRect rect = transform_state.LastPlanarQuad().BoundingBox();
     rect.SetHeight(Table()->LogicalHeight());
     transform_state.SetQuad(FloatQuad(rect));
   }
   return LayoutTableBoxComponent::MapToVisualRectInAncestorSpaceInternal(
       ancestor, transform_state, flags);
 }
 
 bool LayoutTableSection::PaintedOutputOfObjectHasNoEffectRegardlessOfSize()
     const {
   // LayoutTableSection paints background from columns.
   if (Table()->HasColElements())
     return false;
   return LayoutTableBoxComponent::
       PaintedOutputOfObjectHasNoEffectRegardlessOfSize();
 }
 
 }  // namespace blink