Repeat footers in paginated context

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1121 matching lines @@
   line_box.SetIsFirstAfterPageBreak(false);
   LayoutState* layout_state = View()->GetLayoutState();
   if (!layout_state->IsPaginated())
     return;
   if (!IsPageLogicalHeightKnown())
     return;
   LayoutUnit page_logical_height = PageLogicalHeightForOffset(logical_offset);
   LayoutUnit remaining_logical_height = PageRemainingLogicalHeightForOffset(
       logical_offset, kAssociateWithLatterPage);
   int line_index = LineCount(&line_box);
-  if (remaining_logical_height < line_height ||
+  // We need to detect if we overlap a repeating footer and if so take the
+  // full remaining logical height as our strut to the next page.
+  LayoutUnit remaining_logical_height_including_footer =
+      remaining_logical_height - layout_state->HeightOffsetForTableFooters();
+  if (remaining_logical_height_including_footer < line_height ||
       (ShouldBreakAtLineToAvoidWidow() &&
        LineBreakToAvoidWidow() == line_index)) {
     LayoutUnit pagination_strut = CalculatePaginationStrutToFitContent(
         logical_offset, remaining_logical_height, line_height);
     LayoutUnit new_logical_offset = logical_offset + pagination_strut;
     // Moving to a different page or column may mean that its height is
     // different.
     page_logical_height = PageLogicalHeightForOffset(new_logical_offset);
     if (line_height > page_logical_height) {
       // Too tall to fit in one page / column. Give up. Don't push to the next
@@ skipping 86 matching lines @@
     return logical_offset;
   LayoutUnit child_logical_height = LogicalHeightForChild(child);
   // Floats' margins do not collapse with page or column boundaries.
   if (child.IsFloating())
     child_logical_height +=
         MarginBeforeForChild(child) + MarginAfterForChild(child);
   if (!IsPageLogicalHeightKnown())
     return logical_offset;
   LayoutUnit remaining_logical_height = PageRemainingLogicalHeightForOffset(
       logical_offset, kAssociateWithLatterPage);
-  if (remaining_logical_height >= child_logical_height)
+  LayoutUnit remaining_logical_height_including_footer =
+      remaining_logical_height -
+      View()->GetLayoutState()->HeightOffsetForTableFooters();
+  if (remaining_logical_height_including_footer >= child_logical_height)

[mstensho (USE GERRIT), 2017/07/17 10:38:08]

Why can't PageRemainingLogicalHeightForOffset() do this job? Look at all the
call sites for PageRemainingLogicalHeightForOffset(). And we only care about
footers at two of these sites?

[rhogan, 2017/07/24 18:56:06]

Because, as well as deciding whether the line or block fits on the page,
PageRemainingLogicalHeightForOffset() is used to figure out the strut we need to
apply to reach the top of the next page. When we have a footer it can be used
for the latter but not the former - we need to adjust its value by the height of
the footer in order to that.

[mstensho (USE GERRIT), 2017/07/25 08:59:32]

Ah, true.

PageRemainingLogicalHeightForOffset() should definitely take footers into
account. Otherwise it's not really answering how much space we have left.

Maybe CalculatePaginationStrutToFitContent() should always be used to calculate
the strut. Then it probably shouldn't take this |strut_to_next_page| parameter
anymore, since it's going to be impossible for the caller to calculate it.

How about this: https://chromium-review.googlesource.com/c/583619/

Then, afterwards, you can fix PageRemainingLogicalHeightForOffset() and
CalculatePaginationStrutToFitContent() to deal correctly with footers?

     return logical_offset;  // It fits fine where it is. No need to break.
   LayoutUnit pagination_strut = CalculatePaginationStrutToFitContent(
       logical_offset, remaining_logical_height, child_logical_height);
   if (pagination_strut == remaining_logical_height &&
       remaining_logical_height == PageLogicalHeightForOffset(logical_offset)) {
     // Don't break if we were at the top of a page, and we failed to fit the
     // content completely. No point in leaving a page completely blank.
     return logical_offset;
   }
 
@@ skipping 3493 matching lines @@
   return LayoutBlock::DeprecatedInvalidatePaint(paint_invalidation_state);
 }
 
 void LayoutBlockFlow::InvalidateDisplayItemClients(
     PaintInvalidationReason invalidation_reason) const {
   BlockFlowPaintInvalidator(*this).InvalidateDisplayItemClients(
       invalidation_reason);
 }
 
 }  // namespace blink