Initial support for nested multicol layout.

Source/core/layout/LayoutMultiColumnFlowThread.cpp

Index: Source/core/layout/LayoutMultiColumnFlowThread.cpp
diff --git a/Source/core/layout/LayoutMultiColumnFlowThread.cpp b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
index 4e2041b5546e9daf9cd5d8394e4e43e356191e9a..478f89d9d701fd067c66d0e799cfbdb7284497dc 100644
--- a/Source/core/layout/LayoutMultiColumnFlowThread.cpp
+++ b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
@@ -28,6 +28,7 @@
 
 #include "core/layout/LayoutMultiColumnSet.h"
 #include "core/layout/LayoutMultiColumnSpannerPlaceholder.h"
+#include "core/layout/MultiColumnFragmentainerGroup.h"
 
 namespace blink {
 
@@ -270,10 +271,7 @@ LayoutSize LayoutMultiColumnFlowThread::columnOffset(const LayoutPoint& point) c
 
     LayoutPoint flowThreadPoint = flipForWritingMode(point);
     LayoutUnit blockOffset = isHorizontalWritingMode() ? flowThreadPoint.y() : flowThreadPoint.x();
-    LayoutMultiColumnSet* columnSet = columnSetAtBlockOffset(blockOffset);
-    if (!columnSet)
-        return LayoutSize(0, 0);
-    return columnSet->flowThreadTranslationAtOffset(blockOffset);
+    return flowThreadTranslationAtOffset(blockOffset);
 }
 
 bool LayoutMultiColumnFlowThread::needsNewWidth() const
@@ -284,6 +282,21 @@ bool LayoutMultiColumnFlowThread::needsNewWidth() const
     return newWidth != logicalWidth();
 }
 
+bool LayoutMultiColumnFlowThread::isPageLogicalHeightKnown() const
+{
+    if (LayoutMultiColumnSet* columnSet = lastMultiColumnSet())
+        return columnSet->isPageLogicalHeightKnown();
+    return false;
+}
+
+LayoutSize LayoutMultiColumnFlowThread::flowThreadTranslationAtOffset(LayoutUnit offsetInFlowThread) const
+{
+    LayoutMultiColumnSet* columnSet = columnSetAtBlockOffset(offsetInFlowThread);
+    if (!columnSet)
+        return LayoutSize(0, 0);
+    return columnSet->flowThreadTranslationAtOffset(offsetInFlowThread);
+}
+
 LayoutPoint LayoutMultiColumnFlowThread::visualPointToFlowThreadPoint(const LayoutPoint& visualPoint) const
 {
     LayoutUnit blockOffset = isHorizontalWritingMode() ? visualPoint.y() : visualPoint.x();
@@ -344,6 +357,8 @@ void LayoutMultiColumnFlowThread::layoutColumns(bool relayoutChildren, SubtreeLa
         return;
     }
 
+    m_blockOffsetInEnclosingFlowThread = enclosingFlowThread() ? multiColumnBlockFlow()->offsetFromLogicalTopOfFirstPage() : LayoutUnit();
+
     for (LayoutBox* columnBox = firstMultiColumnBox(); columnBox; columnBox = columnBox->nextSiblingMultiColumnBox()) {
         if (!columnBox->isLayoutMultiColumnSet()) {
             ASSERT(columnBox->isLayoutMultiColumnSpannerPlaceholder()); // no other type is expected.
@@ -421,6 +436,46 @@ bool LayoutMultiColumnFlowThread::removeSpannerPlaceholderIfNoLongerValid(Layout
     return true;
 }
 
+LayoutMultiColumnFlowThread* LayoutMultiColumnFlowThread::enclosingFlowThread() const
+{
+    if (multiColumnBlockFlow()->isInsideFlowThread())
+        return toLayoutMultiColumnFlowThread(locateFlowThreadContainingBlockOf(*multiColumnBlockFlow()));
+    return nullptr;
+}
+
+bool LayoutMultiColumnFlowThread::hasFragmentainerGroupForColumnAt(LayoutUnit offsetInFlowThread) const
+{
+    // If there's no enclosing flow thread, there'll always be only one fragmentainer group, and it
+    // can hold as many columns as we like. We shouldn't even be here in that case.
+    ASSERT(enclosingFlowThread());
+
+    LayoutMultiColumnSet* lastColumnSet = lastMultiColumnSet();
+    if (!lastColumnSet) {
+        ASSERT_NOT_REACHED();
+        return true;
+    }
+    if (lastColumnSet->logicalTopInFlowThread() > offsetInFlowThread)
+        return true;
+    const MultiColumnFragmentainerGroup& lastRow = lastColumnSet->lastFragmentainerGroup();
+    if (lastRow.logicalTopInFlowThread() > offsetInFlowThread)
+        return true;
+    return offsetInFlowThread - lastRow.logicalTopInFlowThread() < lastRow.logicalHeight() * lastColumnSet->usedColumnCount();
+}
+
+void LayoutMultiColumnFlowThread::appendNewFragmentainerGroupIfNeeded(LayoutUnit offsetInFlowThread)
+{
+    LayoutMultiColumnFlowThread* enclosingFlowThread = this->enclosingFlowThread();
+    if (!enclosingFlowThread)
+        return; // Not nested. We'll never need more rows than the one we already have then.
+    if (!hasFragmentainerGroupForColumnAt(offsetInFlowThread)) {
+        // We have run out of columns here, so we add another row to hold more columns. When we add
+        // a new row, it implicitly means that we're inserting another column in our enclosing
+        // multicol container. That in turn may mean that we've run out of columns there too.
+        const MultiColumnFragmentainerGroup& newRow = lastMultiColumnSet()->appendNewFragmentainerGroup();
+        enclosingFlowThread->appendNewFragmentainerGroupIfNeeded(newRow.blockOffsetInEnclosingFlowThread());
+    }
+}
+
 void LayoutMultiColumnFlowThread::calculateColumnCountAndWidth(LayoutUnit& width, unsigned& count) const
 {
     LayoutBlock* columnBlock = multiColumnBlockFlow();
@@ -916,11 +971,4 @@ bool LayoutMultiColumnFlowThread::addForcedColumnBreak(LayoutUnit offset, Layout
     return false;
 }
 
-bool LayoutMultiColumnFlowThread::isPageLogicalHeightKnown() const
-{
-    if (LayoutMultiColumnSet* columnSet = lastMultiColumnSet())
-        return columnSet->isPageLogicalHeightKnown();
-    return false;
-}
-
 }