[css-grid] Implementation of Baseline Self-Alignment

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

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/layout/BaselineAlignment.h"
+
+namespace blink {
+
+BaselineGroup::BaselineGroup(WritingMode blockFlow,
+                             ItemPosition childPreference)
+    : m_maxAscent(0), m_maxDescent(0), m_items() {
+  m_blockFlow = blockFlow;
+  m_preference = childPreference;
+}
+
+void BaselineGroup::update(const LayoutBox& child,
+                           LayoutUnit ascent,
+                           LayoutUnit descent) {
+  if (m_items.insert(&child).isNewEntry) {
+    m_maxAscent = std::max(m_maxAscent, ascent);
+    m_maxDescent = std::max(m_maxDescent, descent);
+  }
+}
+
+bool BaselineGroup::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 BaselineGroup::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;
+  }
+}
+
+bool BaselineGroup::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);
+}
+
+BaselineContext::BaselineContext(const LayoutBox& child,
+                                 ItemPosition preference,
+                                 LayoutUnit ascent,
+                                 LayoutUnit descent) {
+  DCHECK(isBaselinePosition(preference));
+  updateSharedGroup(child, preference, ascent, descent);
+}
+
+const BaselineGroup& BaselineContext::getSharedGroup(
+    const LayoutBox& child,
+    ItemPosition preference) const {
+  DCHECK(isBaselinePosition(preference));
+  return const_cast<BaselineContext*>(this)->findCompatibleSharedGroup(
+      child, preference);
+}
+
+void BaselineContext::updateSharedGroup(const LayoutBox& child,
+                                        ItemPosition preference,
+                                        LayoutUnit ascent,
+                                        LayoutUnit descent) {
+  DCHECK(isBaselinePosition(preference));
+  BaselineGroup& group = findCompatibleSharedGroup(child, preference);
+  group.update(child, ascent, descent);
+}
+
+// TODO Properly implement baseline-group compatibility
+// See https://github.com/w3c/csswg-drafts/issues/721
+BaselineGroup& BaselineContext::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.push_front(BaselineGroup(blockDirection, preference));
+  return m_sharedGroups[0];
+}
+
+}  // namespace blink