Calculate minimum column height after layout.

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

Index: third_party/WebKit/Source/core/layout/ColumnBalancer.cpp
diff --git a/third_party/WebKit/Source/core/layout/ColumnBalancer.cpp b/third_party/WebKit/Source/core/layout/ColumnBalancer.cpp
index 65d3f4cb8a107682d467ffffa3ec44b395e26cc3..eb25bbf3d8e57a162f64f3bb443dcd56b65b7e5f 100644
--- a/third_party/WebKit/Source/core/layout/ColumnBalancer.cpp
+++ b/third_party/WebKit/Source/core/layout/ColumnBalancer.cpp
@@ -25,13 +25,14 @@ void ColumnBalancer::traverseSubtree(const LayoutBox& box)
 {
     if (box.childrenInline() && box.isLayoutBlockFlow()) {
         // Look for breaks between lines.
-        for (const RootInlineBox* line = toLayoutBlockFlow(box).firstRootBox(); line; line = line->nextRootBox()) {
+        const LayoutBlockFlow& blockFlow = toLayoutBlockFlow(box);
+        for (const RootInlineBox* line = blockFlow.firstRootBox(); line; line = line->nextRootBox()) {
             LayoutUnit lineTopInFlowThread = m_flowThreadOffset + line->lineTopWithLeading();
             if (lineTopInFlowThread < group().logicalTopInFlowThread())
                 continue;
             if (lineTopInFlowThread >= group().logicalBottomInFlowThread())
                 break;
-            examineLine(*line);
+            examineLine(blockFlow, *line);
         }
     }
 
@@ -92,7 +93,8 @@ LayoutUnit InitialColumnHeightFinder::initialMinimalBalancedHeight() const
 {
     unsigned index = contentRunIndexWithTallestColumns();
     LayoutUnit startOffset = index > 0 ? m_contentRuns[index - 1].breakOffset() : group().logicalTopInFlowThread();
-    return m_contentRuns[index].columnLogicalHeight(startOffset);
+    LayoutUnit logicalHeightEstimate = m_contentRuns[index].columnLogicalHeight(startOffset);
+    return std::max(logicalHeightEstimate, m_minimumColumnLogicalHeight);
 }
 
 void InitialColumnHeightFinder::examineBoxAfterEntering(const LayoutBox& box)
@@ -107,16 +109,38 @@ void InitialColumnHeightFinder::examineBoxAfterEntering(const LayoutBox& box)
 
     if (box.hasForcedBreakAfter())
         addContentRun(flowThreadOffset() + box.logicalHeight());
+
+    if (box.paginationBreakability() != LayoutBox::AllowAnyBreaks) {

[leviw_travelin_and_unemployed, 2015/11/05 18:44:26]

This is new code?

[mstensho (USE GERRIT), 2015/11/05 19:15:56]

This used to be handled in LayoutBlockFlow::adjustForUnsplittableChild(), by
calling updateMinimumHeight().

+        LayoutUnit unsplittableLogicalHeight = box.logicalHeight();
+        if (box.isFloating())
+            unsplittableLogicalHeight += box.marginBefore() + box.marginAfter();
+        if (m_minimumColumnLogicalHeight < unsplittableLogicalHeight)
+            m_minimumColumnLogicalHeight = unsplittableLogicalHeight;
+    }
 }
 
 void InitialColumnHeightFinder::examineBoxBeforeLeaving(const LayoutBox& box)
 {
 }
 
-void InitialColumnHeightFinder::examineLine(const RootInlineBox& line)
+static inline LayoutUnit columnLogicalHeightRequirementForLine(const ComputedStyle& style, const RootInlineBox& lastLine)
+{
+    // We may require a certain minimum number of lines per page in order to satisfy
+    // orphans and widows, and that may affect the minimum page height.
+    unsigned lineCount = std::max<unsigned>(style.hasAutoOrphans() ? 1 : style.orphans(), style.widows());

[leviw_travelin_and_unemployed, 2015/11/05 18:44:26]

minimumLineCount?

[mstensho (USE GERRIT), 2015/11/05 19:15:56]

Good idea. This code was just copied from LayoutBlockFlow.

[mstensho (USE GERRIT), 2015/11/05 22:17:10]

Done.

+    const RootInlineBox* firstLine = &lastLine;
+    for (unsigned i = 1; i < lineCount && firstLine->prevRootBox(); i++)
+        firstLine = firstLine->prevRootBox();
+    return lastLine.lineBottomWithLeading() - firstLine->lineTopWithLeading();
+}
+
+void InitialColumnHeightFinder::examineLine(const LayoutBlockFlow& containingBlock, const RootInlineBox& line)
 {
     LayoutUnit lineTop = line.lineTopWithLeading();
     LayoutUnit lineTopInFlowThread = flowThreadOffset() + lineTop;
+    LayoutUnit minimumLogialHeight = columnLogicalHeightRequirementForLine(containingBlock.styleRef(), line);
+    if (m_minimumColumnLogicalHeight < minimumLogialHeight)
+        m_minimumColumnLogicalHeight = minimumLogialHeight;
     ASSERT(isFirstAfterBreak(lineTopInFlowThread) || !line.paginationStrut());
     if (isFirstAfterBreak(lineTopInFlowThread))
         recordStrutBeforeOffset(lineTopInFlowThread, line.paginationStrut());
@@ -262,7 +286,7 @@ void MinimumSpaceShortageFinder::examineBoxBeforeLeaving(const LayoutBox& box)
     m_pendingStrut = LayoutUnit::min();
 }
 
-void MinimumSpaceShortageFinder::examineLine(const RootInlineBox& line)
+void MinimumSpaceShortageFinder::examineLine(const LayoutBlockFlow& containingBlock, const RootInlineBox& line)
 {
     LayoutUnit lineTop = line.lineTopWithLeading();
     LayoutUnit lineTopInFlowThread = flowThreadOffset() + lineTop;