Display table header groups at the top of each page

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

Index: third_party/WebKit/Source/core/paint/TablePainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/TablePainter.cpp b/third_party/WebKit/Source/core/paint/TablePainter.cpp
index 0e1ea132e9dc1facd49a7aaa19d08bcd1fdf3c12..d2da724433ca7a4b21516e4e625e25b2595656bd 100644
--- a/third_party/WebKit/Source/core/paint/TablePainter.cpp
+++ b/third_party/WebKit/Source/core/paint/TablePainter.cpp
@@ -6,6 +6,7 @@
 
 #include "core/layout/LayoutTable.h"
 #include "core/layout/LayoutTableSection.h"
+#include "core/layout/LayoutView.h"
 #include "core/style/CollapsedBorderValue.h"
 #include "core/paint/BoxClipper.h"
 #include "core/paint/BoxPainter.h"
@@ -17,6 +18,32 @@
 
 namespace blink {
 
+void TablePainter::paintRepeatingHeaderGroup(const PaintInfo& paintInfo, const LayoutPoint& paintOffset, LayoutBox* child, const CollapsedBorderValue& currentBorderValue, ItemToPaint itemToPaint)

[Xianzhu, 2016/05/31 02:11:33]

Pass paintInfoForDescendants from caller, then you can avoid
paintInfo.forDescendants()) in this function. 

[Xianzhu, 2016/06/01 19:19:39]

s/LayoutBox* child/const LayoutTableSection& headerSection/

+{
+    if (m_layoutTable.header() != child)
+        return;
+    if (child->getPaginationBreakability() == LayoutTableBoxComponent::AllowAnyBreaks)

[Xianzhu, 2016/05/31 02:11:33]

Use LayoutBox::AllowAnyBreaks.

+        return;
+    LayoutUnit printedPageLogicalHeight = child->view() ? child->view()->pageLogicalHeight() : LayoutUnit();
+    LayoutUnit pageHeight = std::max(printedPageLogicalHeight, m_layoutTable.flowThreadContainingBlock() ? m_layoutTable.pageLogicalHeightForOffset(LayoutUnit()) : LayoutUnit());
+    if (!pageHeight)
+        return;
+
+    int pages = static_cast<int>(ceilf(m_layoutTable.logicalHeight() / pageHeight));
+    LayoutPoint paginationOffset = paintOffset;
+    paginationOffset += LayoutPoint(0, pageHeight - m_layoutTable.pageLogicalOffset());
+    for (int i = 1; i < pages; i++) {
+        LayoutPoint childPoint = m_layoutTable.flipForWritingModeForChild(child, paginationOffset);
+        if (itemToPaint == PaintCollapsedBorders) {
+            LayoutTableSection* section = toLayoutTableSection(child);
+            TableSectionPainter(*section).paintCollapsedBorders(paintInfo.forDescendants(), childPoint, currentBorderValue);

[Xianzhu, 2016/06/01 19:19:39]

Move the common code (LayoutTableSection* section = ...; TableSectionPainter
sectionPainter(*section)) out of the loop.

+        } else {
+            child->paint(paintInfo.forDescendants(), childPoint);
+        }
+        paginationOffset += LayoutPoint(0, pageHeight);
+    }

[Xianzhu, 2016/05/31 02:11:34]

We paint each page as a layer fragment in PaintLayerPainter in a loop, so the
above loop is redundant. Here you should paint for one page only.

[rhogan, 2016/06/01 18:39:46]

Right, but table headers don't have a layer - so the nearest object that will
paint a layer is the flow thread and it won't be able to inspect for table
header groups when collecting fragments. So this is the only place I can think
of for repeating the table headers across each page.

Maybe I'm missing something?

[Xianzhu, 2016/06/01 19:19:39]

I think this is the right place (and TableSectionPainter is more appropriate,
see comments below).

My comment was about performance. In the above loop, normally only 1 iteration
will actually paint into the cull rect of paintInfo because the cull rect is for
one page/fragment.

However, to make the code not strictly coupled to PaintLayerPainter, you can
keep the loop, but with modified starting and ending value according to the cull
rect to avoid unnecessary iterations.

+}
+
 void TablePainter::paintObject(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     PaintPhase paintPhase = paintInfo.phase;
@@ -39,6 +66,7 @@ void TablePainter::paintObject(const PaintInfo& paintInfo, const LayoutPoint& pa
             if (child->isBox() && !toLayoutBox(child)->hasSelfPaintingLayer() && (child->isTableSection() || child->isTableCaption())) {
                 LayoutPoint childPoint = m_layoutTable.flipForWritingModeForChild(toLayoutBox(child), paintOffset);
                 child->paint(paintInfoForDescendants, childPoint);
+                paintRepeatingHeaderGroup(paintInfo, paintOffset, toLayoutBox(child), CollapsedBorderValue(), PaintChild);

[Xianzhu, 2016/06/01 19:19:39]

This should be in TableSectionPainter::paint(). With this patch you'll miss the
case that the header section has self-painting layer. It may look like:

   TableSectionPainter::paint()
   {
       orignalPaint();
       if (m_layoutTableSection == m_layoutTableSection.table()->header())
           paintRepeatingHeaderGroup();
   }


(Fwiw, TableSectionPainter::paint has two callsites:
1. From TablePainter if the section has no self-painting layer;
2. From PaintLayerPainter if the section has a self-painting layer.)

             }
         }
 
@@ -51,6 +79,7 @@ void TablePainter::paintObject(const PaintInfo& paintInfo, const LayoutPoint& pa
                 for (LayoutTableSection* section = m_layoutTable.bottomSection(); section; section = m_layoutTable.sectionAbove(section)) {
                     LayoutPoint childPoint = m_layoutTable.flipForWritingModeForChild(section, paintOffset);
                     TableSectionPainter(*section).paintCollapsedBorders(paintInfoForDescendants, childPoint, collapsedBorders[i]);
+                    paintRepeatingHeaderGroup(paintInfo, paintOffset, section, collapsedBorders[i], PaintCollapsedBorders);
                 }
             }
         }