Fix table cell background painting

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

Index: third_party/WebKit/Source/core/layout/LayoutTableCol.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTableCol.cpp b/third_party/WebKit/Source/core/layout/LayoutTableCol.cpp
index ab9da43fce5fef66783948fcbd08f5af0ac5076b..f3a4c376a58fe88e98896ad18e09775a9752d7d7 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTableCol.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTableCol.cpp
@@ -160,6 +160,22 @@ LayoutTableCol* LayoutTableCol::enclosingColumnGroup() const
     return parentColumnGroup;
 }
 
+LayoutTableCol* LayoutTableCol::lastColumnInGroup() const
+{
+    ASSERT(this->isTableColumnGroupWithColumnChildren());
+
+    LayoutTableCol* endCol = nullptr;
+    LayoutTableCol* currentCol = this->nextColumn();
+    // If column has children, traverse the children to find last.
+    if (this->firstChild()) {
+        while (currentCol && currentCol->enclosingColumnGroup() == this) {
+            endCol = currentCol;
+            currentCol = currentCol->nextColumn();
+        }
+    }
+    return endCol;
+}
+
 LayoutTableCol* LayoutTableCol::nextColumn() const
 {
     // If |this| is a column-group, the next column is the colgroup's first child column.
@@ -170,8 +186,9 @@ LayoutTableCol* LayoutTableCol::nextColumn() const
     LayoutObject* next = nextSibling();
 
     // Failing that, the child is the last column in a column-group, so the next column is the next column/column-group after its column-group.
-    if (!next && parent()->isLayoutTableCol())
-        next = parent()->nextSibling();
+    auto p = parent();
+    if (!next && p && p->isLayoutTableCol())
+        next = p->nextSibling();
 
     for (; next && !next->isLayoutTableCol(); next = next->nextSibling()) { }
 
@@ -200,4 +217,100 @@ const BorderValue& LayoutTableCol::borderAdjoiningCellAfter(const LayoutTableCel
     return style()->borderEnd();
 }
 
+LayoutRect LayoutTableCol::positionForBackgroundDrawing(unsigned absoluteColumnIndex) const
+{
+
+    // Table spec weirdness alert:
+    // <col> elements need to provide absoluteColumnIndex because
+    // <col> element with span N is treated for display as
+    // N <col> elements with span 1. It does not make sense to talk
+    // about visual <col> position, only about <col> position at a
+    // particular absolute column.
+
+    LayoutTable * table = this->table();
+    LayoutRect position;
+
+    if (!table)
+        return position;
+
+    LayoutTableSection* topSection = table->topNonEmptySection();
+    LayoutTableSection* bottomSection = table->bottomNonEmptySection();
+    if (!topSection || !bottomSection)
+        return position;
+
+    Vector<unsigned> colIndexes = getEffectiveColumnIndexes();
+
+    if (colIndexes.size() == 0)
+        return position;
+
+    unsigned startColumnIndex = colIndexes[0];
+    unsigned endColumnIndex = colIndexes.last();
+
+    // Tricky: if <col> has a span, we need to pick a <col> of width 1
+    // that starts at absoluteColumnIndex
+    if (isTableColumn() && colIndexes.size() > 1) {
+        unsigned wantedEffectiveColumn = table->absoluteColumnToEffectiveColumn(absoluteColumnIndex);
+        size_t wantedIt = colIndexes.find(wantedEffectiveColumn);
+        ASSERT(wantedIt != kNotFound);
+        startColumnIndex = colIndexes[wantedIt];
+        endColumnIndex = startColumnIndex;
+    }
+    position = topSection->getCellPhysicalPosition(0, startColumnIndex);
+    position.moveBy(topSection->location());
+    LayoutRect bottomPosition = bottomSection->getCellPhysicalPosition(bottomSection->numRows() - 1, endColumnIndex);
+    bottomPosition.moveBy(bottomSection->location());
+    position.uniteEvenIfEmpty(bottomPosition);
+    return position;
+}
+
+Vector<unsigned> LayoutTableCol::getEffectiveColumnIndexes() const
+{
+    LayoutTable * table = this->table();
+    Vector<unsigned> indexes;
+
+    if (!table)
+        return indexes;
+
+    unsigned lastEffectiveColumn = table->lastEffectiveColumnIndex();
+
+    if (isTableColumn()) {
+        unsigned idx = table->colElementToAbsoluteColumn(this);
+        auto span = this->span();
+        unsigned lastSeenColumn = 0xFFFFFFFF;
+        while (span--) {
+            unsigned effectiveColumn = table->absoluteColumnToEffectiveColumn(idx++);
+            if (effectiveColumn != lastSeenColumn && effectiveColumn <= lastEffectiveColumn) {
+                indexes.append(effectiveColumn);
+                lastSeenColumn = effectiveColumn;
+            }
+        }
+    } else { // isTableColumnGroup.
+        if (isTableColumnGroupWithColumnChildren()) {
+            LayoutTableCol* currentCol = nullptr;
+            auto lastCol = lastColumnInGroup();
+            do {
+                currentCol = currentCol ? currentCol->nextColumn() : nextColumn();
+                if (currentCol) {
+                    auto colIndexes = currentCol->getEffectiveColumnIndexes();
+                    for (auto c = colIndexes.begin(); c != colIndexes.end(); c++)
+                        indexes.append(*c);
+                }
+            } while (currentCol && currentCol != lastCol);
+        } else { // tableColumnGroup with no children.
+            // It extends over 'span' absolute columns.
+            unsigned idx = table->colElementToAbsoluteColumn(this);
+            auto span = this->span();
+            unsigned lastSeenColumn = 0xFFFFFFFF;
+            while (span--) {
+                unsigned effectiveColumn = table->absoluteColumnToEffectiveColumn(idx++);
+                if (effectiveColumn != lastSeenColumn && effectiveColumn <= lastEffectiveColumn) {
+                    indexes.append(effectiveColumn);
+                    lastSeenColumn = effectiveColumn;
+                }
+            }
+        }
+    }
+    return indexes;
+}
+
 } // namespace blink