[css-grid] Implementation of Baseline Self-Alignment

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

Index: third_party/WebKit/Source/core/layout/LayoutGrid.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutGrid.cpp b/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
index eef54fb123031d0c59c34df4a23d138abee928e3..97bd60d359f5c4b5cf0867474b4588c02ec81e06 100644
--- a/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
@@ -33,6 +33,7 @@
 #include "core/style/ComputedStyle.h"
 #include "core/style/GridArea.h"
 #include "platform/LengthFunctions.h"
+#include "platform/text/WritingMode.h"
 #include "wtf/PtrUtil.h"
 #include <algorithm>
 #include <memory>
@@ -43,6 +44,11 @@ static const int infinity = -1;
 
 class GridItemWithSpan;
 
+static inline bool isBaselinePosition(ItemPosition position) {
+  return position == ItemPositionBaseline ||
+         position == ItemPositionLastBaseline;
+}
+
 size_t LayoutGrid::Grid::numTracks(GridTrackSizingDirection direction) const {
   if (direction == ForRows)
     return m_grid.size();
@@ -282,6 +288,110 @@ struct ContentAlignmentData {
   LayoutUnit distributionOffset = LayoutUnit(-1);
 };
 
+class BaselineGroup {
+ public:
+  BaselineGroup(WritingMode blockFlow, ItemPosition childPreference)
+      : m_maxAscent(0), m_maxDescent(0), m_items() {
+    m_blockFlow = blockFlow;
+    m_preference = childPreference;
+  }
+
+  void update(const LayoutBox& child, LayoutUnit ascent, LayoutUnit descent) {
+    if (m_items.add(&child).isNewEntry) {
+      m_maxAscent = std::max(m_maxAscent, ascent);
+      m_maxDescent = std::max(m_maxDescent, descent);
+    }
+  }
+  bool isCompatible(WritingMode childBlockFlow,
+                    ItemPosition childPreference) const {
+    DCHECK(isBaselinePosition(childPreference));
+    DCHECK_GT(size(), 0);
+    return ((m_blockFlow == childBlockFlow ||
+             isOrthogonalBlockFlow(childBlockFlow)) &&
+            m_preference == childPreference) ||
+           (isOppositeBlockFlow(childBlockFlow) &&
+            m_preference != childPreference);
+  }
+
+  LayoutUnit maxAscent() const { return m_maxAscent; }
+  LayoutUnit maxDescent() const { return m_maxDescent; }
+  int size() const { return m_items.size(); }
+
+ private:
+  bool isOppositeBlockFlow(WritingMode blockFlow) const {
+    switch (blockFlow) {
+      case WritingMode::kHorizontalTb:
+        return false;
+      case WritingMode::kVerticalLr:
+        return m_blockFlow == WritingMode::kVerticalRl;
+      case WritingMode::kVerticalRl:
+        return m_blockFlow == WritingMode::kVerticalLr;
+      default:
+        NOTREACHED();
+        return false;
+    }
+  }
+  bool isOrthogonalBlockFlow(WritingMode blockFlow) const {
+    switch (blockFlow) {
+      case WritingMode::kHorizontalTb:
+        return m_blockFlow != WritingMode::kHorizontalTb;
+      case WritingMode::kVerticalLr:
+      case WritingMode::kVerticalRl:
+        return m_blockFlow == WritingMode::kHorizontalTb;
+      default:
+        NOTREACHED();
+        return false;
+    }
+  }
+
+  WritingMode m_blockFlow;
+  ItemPosition m_preference;
+  LayoutUnit m_maxAscent;
+  LayoutUnit m_maxDescent;
+  HashSet<const LayoutBox*> m_items;
+};
+
+class BaselineContext {
+ public:
+  BaselineContext(const LayoutBox& child,
+                  ItemPosition preference,
+                  LayoutUnit ascent,
+                  LayoutUnit descent) {
+    DCHECK(isBaselinePosition(preference));
+    updateSharedGroup(child, preference, ascent, descent);
+  }
+  const BaselineGroup& getSharedGroup(const LayoutBox& child,
+                                      ItemPosition preference) const {
+    DCHECK(isBaselinePosition(preference));
+    return const_cast<BaselineContext*>(this)->findCompatibleSharedGroup(
+        child, preference);
+  }
+  void updateSharedGroup(const LayoutBox& child,
+                         ItemPosition preference,
+                         LayoutUnit ascent,
+                         LayoutUnit descent) {
+    DCHECK(isBaselinePosition(preference));
+    BaselineGroup& group = findCompatibleSharedGroup(child, preference);
+    group.update(child, ascent, descent);
+  }
+
+ private:
+  // TODO Properly implement baseline-group compatibility
+  // See https://github.com/w3c/csswg-drafts/issues/721
+  BaselineGroup& findCompatibleSharedGroup(const LayoutBox& child,
+                                           ItemPosition preference) {
+    WritingMode blockDirection = child.styleRef().getWritingMode();
+    for (auto& group : m_sharedGroups) {
+      if (group.isCompatible(blockDirection, preference))
+        return group;
+    }
+    m_sharedGroups.prepend(BaselineGroup(blockDirection, preference));
+    return m_sharedGroups[0];
+  }
+
+  Vector<BaselineGroup> m_sharedGroups;
+};

[svillar, 2017/01/19 09:41:25]

These two classes have nothing to do with Grid, they're both pretty general.
Would it make sense to isolate them in a different file so they could be reused
for other LayoutObjects?

[jfernandez, 2017/01/19 16:31:48]

Acknowledged.

+
 enum TrackSizeRestriction {
   AllowInfinity,
   ForbidInfinity,
@@ -389,6 +499,12 @@ class LayoutGrid::GridIterator {
   size_t m_childIndex;
 };
 
+typedef HashMap<unsigned,
+                std::unique_ptr<BaselineContext>,
+                DefaultHash<unsigned>::Hash,
+                WTF::UnsignedWithZeroKeyHashTraits<unsigned>>
+    BaselineContextsMap;
+
 struct LayoutGrid::GridSizingData {
   WTF_MAKE_NONCOPYABLE(GridSizingData);
   STACK_ALLOCATED();
@@ -401,6 +517,9 @@ struct LayoutGrid::GridSizingData {
   Vector<GridTrack> rowTracks;
   Vector<size_t> contentSizedTracksIndex;
 
+  BaselineContextsMap rowAxisAlignmentContext;
+  BaselineContextsMap colAxisAlignmentContext;
+
   // Performance optimization: hold onto these Vectors until the end of Layout
   // to avoid repeated malloc / free.
   Vector<GridTrack*> filteredTracks;
@@ -645,6 +764,8 @@ void LayoutGrid::layoutBlock(bool relayoutChildren) {
     GridSizingData sizingData(numTracks(ForColumns, m_grid),
                               numTracks(ForRows, m_grid), m_grid);
 
+    computeBaselineAlignmentContext(sizingData);
+
     // 1- First, the track sizing algorithm is used to resolve the sizes of the
     // grid columns.
     // At this point the logical width is always definite as the above call to
@@ -806,6 +927,7 @@ void LayoutGrid::computeIntrinsicLogicalWidths(
   GridSizingData sizingData(numTracks(ForColumns, grid),
                             numTracks(ForRows, grid), grid);
 
+  computeBaselineAlignmentContext(sizingData);
   computeTrackSizesForIndefiniteSize(ForColumns, sizingData, minLogicalWidth,
                                      maxLogicalWidth);
 
@@ -1324,6 +1446,12 @@ LayoutUnit LayoutGrid::logicalHeightForChild(LayoutBox& child,
     child.clearOverrideLogicalContentHeight();
 
   child.layoutIfNeeded();
+  GridAxis baselineAxis =
+      isOrthogonalChild(child) ? GridRowAxis : GridColumnAxis;
+  if (isBaselineAlignmentForChild(child, baselineAxis)) {
+    auto group = getBaselineGroupForChild(child, sizingData, baselineAxis);
+    return group.maxAscent() + group.maxDescent();
+  }
   return child.logicalHeight() + child.marginLogicalHeight();
 }
 
@@ -1427,6 +1555,10 @@ LayoutUnit LayoutGrid::minContentForChild(LayoutBox& child,
   if (direction == ForColumns &&
       sizingData.sizingOperation == IntrinsicSizeComputation) {
     DCHECK(isOrthogonalChild(child));
+    if (isBaselineAlignmentForChild(child, GridRowAxis)) {
+      auto group = getBaselineGroupForChild(child, sizingData, GridRowAxis);
+      return group.maxAscent() + group.maxDescent();
+    }
     return child.logicalHeight() + child.marginLogicalHeight();
   }
 
@@ -3088,8 +3220,6 @@ static int synthesizedBaselineFromBorderBox(const LayoutBox& box,
       .toInt();
 }
 
-// TODO(lajava): This logic is shared by LayoutFlexibleBox, so it might be
-// refactored somehow.
 int LayoutGrid::baselinePosition(FontBaseline,
                                  bool,
                                  LineDirectionMode direction,
@@ -3103,11 +3233,6 @@ int LayoutGrid::baselinePosition(FontBaseline,
   return baseline + beforeMarginInLineDirection(direction);
 }
 
-bool LayoutGrid::isInlineBaselineAlignedChild(const LayoutBox* child) const {
-  return alignSelfForChild(*child).position() == ItemPositionBaseline &&
-         !isOrthogonalChild(*child) && !hasAutoMarginsInColumnAxis(*child);
-}
-
 int LayoutGrid::firstLineBoxBaseline() const {
   if (isWritingModeRoot() || !m_grid.hasGridItems())
     return -1;
@@ -3120,8 +3245,8 @@ int LayoutGrid::firstLineBoxBaseline() const {
     for (size_t index = 0; index < m_grid.cell(0, column).size(); index++) {
       const LayoutBox* child = m_grid.cell(0, column)[index];
       DCHECK(!child->isOutOfFlowPositioned());
-      // If an item participates in baseline alignmen, we select such item.
-      if (isInlineBaselineAlignedChild(child)) {
+      // If an item participates in baseline alignment, we select such item.
+      if (isBaselineAlignmentForChild(*child)) {
         // TODO (lajava): self-baseline and content-baseline alignment
         // still not implemented.
         baselineChild = child;
@@ -3171,6 +3296,163 @@ int LayoutGrid::inlineBlockBaseline(LineDirectionMode direction) const {
   return synthesizedBaselineFromContentBox(*this, direction) + marginHeight;
 }
 
+bool LayoutGrid::isHorizontalGridAxis(GridAxis axis) const {
+  return axis == GridRowAxis ? isHorizontalWritingMode()
+                             : !isHorizontalWritingMode();
+}
+
+bool LayoutGrid::isParallelToBlockAxisForChild(const LayoutBox& child,
+                                               GridAxis axis) const {
+  return axis == GridColumnAxis ? !isOrthogonalChild(child)
+                                : isOrthogonalChild(child);
+}
+
+bool LayoutGrid::isDescentBaselineForChild(const LayoutBox& child,
+                                           GridAxis baselineAxis) const {
+  return isHorizontalGridAxis(baselineAxis) &&
+         !styleRef().isFlippedBlocksWritingMode();
+}
+
+bool LayoutGrid::isBaselineAlignmentForChild(const LayoutBox& child,
+                                             GridAxis baselineAxis) const {
+  bool isColumnAxisBaseline = baselineAxis == GridColumnAxis;
+  ItemPosition align = isColumnAxisBaseline
+                           ? alignSelfForChild(child).position()
+                           : justifySelfForChild(child).position();
+  bool hasAutoMargins = isColumnAxisBaseline ? hasAutoMarginsInColumnAxis(child)
+                                             : hasAutoMarginsInRowAxis(child);
+  return isBaselinePosition(align) && !hasAutoMargins;
+}
+
+const BaselineGroup& LayoutGrid::getBaselineGroupForChild(
+    const LayoutBox& child,
+    const GridSizingData& sizingData,
+    GridAxis baselineAxis) const {
+  DCHECK(isBaselineAlignmentForChild(child, baselineAxis));
+  auto& grid = sizingData.grid();
+  bool isColumnAxisBaseline = baselineAxis == GridColumnAxis;
+  bool isRowAxisContext = isColumnAxisBaseline;
+  auto&& span = isRowAxisContext ? grid.gridItemSpan(child, ForRows)

[svillar, 2017/01/19 09:41:25]

auto&& ???

[jfernandez, 2017/01/19 16:31:48]

Since gridItemSpan returns a temporary object, we either use a const lvalue
reference, which implies copying the temporary object, or using an rvalue
reference. As we won't use/asign the span variable anymore, we can use the
rvalue reference to extend the lifetime of the temporary object and avoid the
copy operation. 

As far as I understand this rvalue reference, it only improves the code if the
type implements the "move semantics"; otherwise it's just equivalent to a const
auto&.

+                                 : grid.gridItemSpan(child, ForColumns);
+  auto& contextsMap = isRowAxisContext ? sizingData.rowAxisAlignmentContext
+                                       : sizingData.colAxisAlignmentContext;
+  auto* context = contextsMap.get(span.startLine());
+  DCHECK(context);
+  ItemPosition align = isColumnAxisBaseline
+                           ? alignSelfForChild(child).position()
+                           : justifySelfForChild(child).position();
+  return context->getSharedGroup(child, align);
+}
+
+LayoutUnit LayoutGrid::marginOverForChild(const LayoutBox& child,
+                                          GridAxis axis) const {
+  return isHorizontalGridAxis(axis) ? child.marginRight() : child.marginTop();
+}
+
+LayoutUnit LayoutGrid::logicalAscentForChild(const LayoutBox& child,
+                                             GridAxis baselineAxis) const {
+  LayoutUnit ascent = ascentForChild(child, baselineAxis);
+  return isDescentBaselineForChild(child, baselineAxis)
+             ? descentForChild(child, ascent, baselineAxis)
+             : ascent;
+}
+
+LayoutUnit LayoutGrid::ascentForChild(const LayoutBox& child,
+                                      GridAxis baselineAxis) const {
+  int baseline = isParallelToBlockAxisForChild(child, baselineAxis)
+                     ? child.firstLineBoxBaseline()
+                     : -1;
+  // We take border-box's bottom if no valid baseline.
+  if (baseline == -1) {

[svillar, 2017/01/19 09:41:25]

Unfortunate that we use the magic -1 but I guess it's what
firstLineBoxBaseline() returns now.

[jfernandez, 2017/01/19 16:31:48]

Yes, we can implement optional, as we do in WebKit, but that's clearly part of a
different patch.

+    baseline = isHorizontalGridAxis(baselineAxis)
+                   ? child.size().width().toInt()
+                   : child.size().height().toInt();
+  }
+  return LayoutUnit(baseline) + marginOverForChild(child, baselineAxis);
+}
+
+LayoutUnit LayoutGrid::descentForChild(const LayoutBox& child,
+                                       LayoutUnit ascent,
+                                       GridAxis baselineAxis) const {
+  if (isParallelToBlockAxisForChild(child, baselineAxis))
+    return child.marginLogicalHeight() + child.logicalHeight() - ascent;
+  return child.marginLogicalWidth() + child.logicalWidth() - ascent;
+}
+
+void LayoutGrid::computeBaselineAlignmentContext(
+    GridSizingData& sizingData) const {
+  for (auto* child = firstInFlowChildBox(); child;
+       child = child->nextInFlowSiblingBox()) {
+    updateBaselineAlignmentContextIfNeeded(*child, sizingData, GridRowAxis);
+    updateBaselineAlignmentContextIfNeeded(*child, sizingData, GridColumnAxis);
+  }
+}
+
+void LayoutGrid::updateBaselineAlignmentContextIfNeeded(
+    LayoutBox& child,
+    GridSizingData& sizingData,
+    GridAxis baselineAxis) const {
+  if (!isBaselineAlignmentForChild(child, baselineAxis))
+    return;
+
+  child.layoutIfNeeded();

[svillar, 2017/01/19 09:41:25]

This method is called by computeBaselineAlignmentContext which is called from
the intrinsic size code. We cannot perform layout operations during intrinsic
size computation. This should trigger an ASSERT.

[jfernandez, 2017/01/19 16:31:48]

I don't know why it doesn't. 
Anyway, what I can do it to avoid the layout operation during intrinsic size
computation, based on the GridSizingData flag.

+
+  // Determine Ascent and Descent values of this child with respect to
+  // its grid container.
+  LayoutUnit ascent = ascentForChild(child, baselineAxis);
+  LayoutUnit descent = descentForChild(child, ascent, baselineAxis);
+  if (isDescentBaselineForChild(child, baselineAxis)) {
+    LayoutUnit temp(ascent);
+    ascent = descent;
+    descent = temp;
+  }
+
+  // Looking up for a shared alignment context perpendicular to the
+  // baseline axis.
+  auto& grid = sizingData.grid();
+  bool isColumnAxisBaseline = baselineAxis == GridColumnAxis;
+  bool isRowAxisContext = isColumnAxisBaseline;
+  auto&& span = isRowAxisContext ? grid.gridItemSpan(child, ForRows)

[svillar, 2017/01/19 09:41:25]

auto&& ?

[jfernandez, 2017/01/19 16:31:48]

Already replied before.

+                                 : grid.gridItemSpan(child, ForColumns);
+  auto& contextsMap = isRowAxisContext ? sizingData.rowAxisAlignmentContext
+                                       : sizingData.colAxisAlignmentContext;
+  auto addResult = contextsMap.add(span.startLine(), nullptr);
+
+  // Looking for a compatible baseline-sharing group.
+  ItemPosition align = isColumnAxisBaseline
+                           ? alignSelfForChild(child).position()
+                           : justifySelfForChild(child).position();
+  if (addResult.isNewEntry) {
+    addResult.storedValue->value =
+        WTF::makeUnique<BaselineContext>(child, align, ascent, descent);
+  } else {
+    auto* context = addResult.storedValue->value.get();
+    context->updateSharedGroup(child, align, ascent, descent);
+  }
+}
+
+LayoutUnit LayoutGrid::columnAxisBaselineOffsetForChild(
+    const LayoutBox& child,
+    const GridSizingData& sizingData) const {
+  if (!isBaselineAlignmentForChild(child, GridColumnAxis))
+    return LayoutUnit();
+  auto& group = getBaselineGroupForChild(child, sizingData, GridColumnAxis);
+  if (group.size() > 1)
+    return group.maxAscent() - logicalAscentForChild(child, GridColumnAxis);
+  return LayoutUnit();
+}
+
+LayoutUnit LayoutGrid::rowAxisBaselineOffsetForChild(
+    const LayoutBox& child,
+    const GridSizingData& sizingData) const {
+  if (!isBaselineAlignmentForChild(child, GridRowAxis))
+    return LayoutUnit();
+  auto& group = getBaselineGroupForChild(child, sizingData, GridRowAxis);
+  if (group.size() > 1)
+    group.maxAscent() - logicalAscentForChild(child, GridRowAxis);
+  return LayoutUnit();
+}
+
 GridAxisPosition LayoutGrid::columnAxisPositionForChild(
     const LayoutBox& child) const {
   bool hasSameWritingMode =
@@ -3240,8 +3522,6 @@ GridAxisPosition LayoutGrid::columnAxisPositionForChild(
       return GridAxisStart;
     case ItemPositionBaseline:
     case ItemPositionLastBaseline:
-      // FIXME: These two require implementing Baseline Alignment. For now, we
-      // always 'start' align the child. crbug.com/234191
       return GridAxisStart;
     case ItemPositionAuto:
     case ItemPositionNormal:
@@ -3319,8 +3599,6 @@ GridAxisPosition LayoutGrid::rowAxisPositionForChild(
       return GridAxisStart;
     case ItemPositionBaseline:
     case ItemPositionLastBaseline:
-      // FIXME: These two require implementing Baseline Alignment. For now, we
-      // always 'start' align the child. crbug.com/234191
       return GridAxisStart;
     case ItemPositionAuto:
     case ItemPositionNormal:
@@ -3343,7 +3621,8 @@ LayoutUnit LayoutGrid::columnAxisOffsetForChild(
   GridAxisPosition axisPosition = columnAxisPositionForChild(child);
   switch (axisPosition) {
     case GridAxisStart:
-      return startPosition;
+      return startPosition +
+             columnAxisBaselineOffsetForChild(child, sizingData);
     case GridAxisEnd:
     case GridAxisCenter: {
       size_t childEndLine = rowsSpan.endLine();
@@ -3387,7 +3666,7 @@ LayoutUnit LayoutGrid::rowAxisOffsetForChild(const LayoutBox& child,
   GridAxisPosition axisPosition = rowAxisPositionForChild(child);
   switch (axisPosition) {
     case GridAxisStart:
-      return startPosition;
+      return startPosition + rowAxisBaselineOffsetForChild(child, sizingData);
     case GridAxisEnd:
     case GridAxisCenter: {
       size_t childEndLine = columnsSpan.endLine();