Repeat footers in paginated context

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

Index: third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp b/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
index 275532bb4fd737759e67a6f72a4a27292d04d4dc..41201952a566eb3f86b48a4f1de8bb997dda9086 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
@@ -1244,7 +1244,12 @@ void LayoutTableSection::LayoutRows() {
 int LayoutTableSection::PaginationStrutForRow(LayoutTableRow* row,
                                               LayoutUnit logical_offset) const {
   DCHECK(row);
-  if (row->GetPaginationBreakability() == kAllowAnyBreaks)
+  const LayoutTableSection* footer = Table()->Footer();
+  bool make_room_for_repeating_footer = footer && footer != this &&
+                                        footer->IsRepeatingFooterGroup(this) &&
+                                        row->RowIndex();
+  if (!make_room_for_repeating_footer &&
+      row->GetPaginationBreakability() == kAllowAnyBreaks)
     return 0;
   LayoutUnit page_logical_height = PageLogicalHeightForOffset(logical_offset);
   if (!page_logical_height)
@@ -1254,6 +1259,9 @@ int LayoutTableSection::PaginationStrutForRow(LayoutTableRow* row,
   if (row_logical_height > page_logical_height)
     return 0;
 
+  if (make_room_for_repeating_footer)
+    row_logical_height += footer->LogicalHeight();
+
   LayoutUnit remaining_logical_height = PageRemainingLogicalHeightForOffset(
       logical_offset, LayoutBlock::kAssociateWithLatterPage);
   if (remaining_logical_height >= row_logical_height)
@@ -2079,8 +2087,9 @@ void LayoutTableSection::AdjustRowForPagination(LayoutTableRow& row_object,
           offset_from_top_of_page <= Table()->VBorderSpacing();
     }
 
-    if (!row_is_at_top_of_column)
+    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
@@ -2096,6 +2105,19 @@ void LayoutTableSection::AdjustRowForPagination(LayoutTableRow& row_object,
   if (row_is_at_top_of_column && offset_from_top_of_page)
     pagination_strut -= offset_from_top_of_page.ToInt();
 
+  LayoutTableSection* footer = Table()->Footer();
+  if (footer && footer != this && header != this &&
+      footer->IsRepeatingFooterGroup(this)) {
+    LayoutUnit offset_from_top = LogicalTop() + row_object.LogicalTop();
+    unsigned page =
+        FloorToInt(offset_from_top / PageLogicalHeightForOffset(LogicalTop()));
+    LayoutUnit remaining_logical_height = PageRemainingLogicalHeightForOffset(
+        row_object.LogicalTop(), kAssociateWithLatterPage);
+    if (remaining_logical_height >=
+        (footer->LogicalHeight() - Table()->VBorderSpacing()))
+      Table()->SetPositionOfRepeatingFooterGroupOnPage(page, offset_from_top);
+  }
+
   // If we have a header group we will paint it at the top of each page,
   // move the rows down to accomodate it.
   if (header && header != this)
@@ -2116,21 +2138,26 @@ void LayoutTableSection::AdjustRowForPagination(LayoutTableRow& row_object,
 }
 
 bool LayoutTableSection::IsRepeatingHeaderGroup() const {
-  if (GetPaginationBreakability() == LayoutBox::kAllowAnyBreaks)
+  if (GetPaginationBreakability() == kAllowAnyBreaks)
     return false;
-  // TODO(rhogan): Should we paint a header repeatedly if it's self-painting?
+
+  // TODO(rhogan): Sections can be self-painting.
   if (HasSelfPaintingLayer())
     return false;
-  LayoutUnit page_height = Table()->PageLogicalHeightForOffset(LayoutUnit());
+
+  LayoutUnit page_height = PageLogicalHeightForOffset(LogicalTop());
   if (!page_height)
     return false;
 
-  if (LogicalHeight() > page_height)
+  // 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;
 
-  // 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
+  // TODO(crbug.com/710387): If the first row of the section after the header
+  // group doesn't fit on the page, then we don't repeat the header on each page
+  // and by extension only support repeating headers on the innermost table in a
+  // set of nested tables.
   LayoutTableSection* section_below = Table()->SectionBelow(this);
   if (!section_below)
     return true;
@@ -2143,23 +2170,50 @@ bool LayoutTableSection::IsRepeatingHeaderGroup() const {
   return true;
 }
 
+bool LayoutTableSection::IsRepeatingFooterGroup(
+    const LayoutTableSection* section_for_page) const {
+  if (GetPaginationBreakability() == kAllowAnyBreaks)
+    return false;
+
+  // TODO(rhogan): Sections can be self-painting.
+  if (HasSelfPaintingLayer())
+    return false;
+
+  // Get the page height for the section that we want to repeat the footer on
+  // so we can see if it fits.
+  LayoutUnit page_height = section_for_page
+                               ? section_for_page->PageLogicalHeightForOffset(
+                                     section_for_page->LogicalTop())

[mstensho (USE GERRIT), 2017/05/10 10:59:03]

First of all, you should probably pass LayoutUnit() here, since the logical
offset parameter in PageLogicalHeightForOffset() is relative to |this|.

It's actually still wrong, though, since you really need the logical offset that
maps to the exact column that you're currently considering. That's only an issue
when we have non-uniform column heights, though (e.g. when printing a multicol
container that crosses page boundaries). I don't think it's super-important to
handle this. Repeated headers and footers are first and foremost useful when
paginating, and not so much inside multicol.

But since this won't work correctly anyway, wouldn't it be better to calculate
(at the beginning of layout) and store a bool is_repeating_footer_group_, so
that we give the same answer every time? The way it works right now, the answer
depends on whether section_for_page is specified or not. It is specified during
layout, but not during painting. I can't see why we'd want this discrepancy.

+                               : PageLogicalHeightForOffset(LogicalTop());

[mstensho (USE GERRIT), 2017/05/10 10:59:03]

Ditto - LayoutUnit() is better. Getting rid of this code altogether would be
even better. :)

+  if (!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()) {
+
+  // Repeating table headers and footers are painted once per fragmentation
+  // page/column. So we need to use the rect for the entire table because
+  // the repeating headers/footers will appear throughout it.
+  if ((Table()->Header() == this && IsRepeatingHeaderGroup()) ||
+      (Table()->Footer() == this && IsRepeatingFooterGroup())) {
     transform_state.Flatten();
     FloatRect rect = transform_state.LastPlanarQuad().BoundingBox();
     rect.SetHeight(Table()->LogicalHeight());
     transform_state.SetQuad(FloatQuad(rect));
+    return Table()->MapToVisualRectInAncestorSpaceInternal(
+        ancestor, transform_state, flags);
   }
   return LayoutTableBoxComponent::MapToVisualRectInAncestorSpaceInternal(
       ancestor, transform_state, flags);