[layoutng] Add helper functions to compute lengths

third_party/WebKit/Source/core/layout/ng/ng_length_utils.cc

+// Copyright 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/ng/ng_length_utils.h"
+
+#include "core/layout/ng/ng_constraint_space.h"
+#include "core/style/ComputedStyle.h"
+#include "platform/LayoutUnit.h"
+#include "platform/Length.h"
+
+namespace blink {
+// TODO(layout-ng):
+// - Handle border-box correctly
+// - positioned and/or replaced calculations
+// - Handle margins for fill-available and width: auto
+
+LayoutUnit resolveInlineLength(LengthResolveType type,
+                               const Length& length,
+                               const NGConstraintSpace& constraintSpace) {
+  DCHECK(!length.isMaxSizeNone());
+  if (type == LengthResolveType::MinSize && length.isAuto())
+    return LayoutUnit();
+  // TODO(layout-ng): Handle min/max/fit-content
+  return valueForLength(length, constraintSpace.inlineContainerSize());
+}
+
+LayoutUnit resolveBlockLength(LengthResolveType type,
+                              const Length& length,
+                              const NGConstraintSpace& constraintSpace,
+                              LayoutUnit contentContribution) {
+  DCHECK(!length.isMaxSizeNone());
+  if (type == LengthResolveType::MinSize && length.isAuto())
+    return LayoutUnit();
+  if (length.isAuto())
+    return contentContribution;
+  if (length.isMinContent() || length.isMaxContent() || length.isFitContent())
+    return contentContribution;
+  return valueForLength(length, constraintSpace.blockContainerSize());
+}
+
+LayoutUnit computeInlineSizeForFragment(
+    const NGConstraintSpace& constraintSpace,
+    const ComputedStyle& style) {
+  LayoutUnit extent = resolveInlineLength(
+      LengthResolveType::ContentSize, style.logicalWidth(), constraintSpace);
+  Length maxLength = style.logicalMaxWidth();
+  if (!maxLength.isMaxSizeNone()) {
+    LayoutUnit max = resolveInlineLength(LengthResolveType::MaxSize, maxLength,
+                                         constraintSpace);
+    extent = std::min(extent, max);
+  }
+  LayoutUnit min = resolveInlineLength(
+      LengthResolveType::MinSize, style.logicalMinWidth(), constraintSpace);
+  extent = std::max(extent, min);
+  if (style.boxSizing() == BoxSizingContentBox) {
+    // TODO(layout-ng): Compute border/padding size and add it
+  }
+  return extent;
+}
+
+LayoutUnit computeBlockSizeForFragment(const NGConstraintSpace& constraintSpace,
+                                       const ComputedStyle& style,
+                                       LayoutUnit contentContribution) {
+  LayoutUnit extent =
+      resolveBlockLength(LengthResolveType::ContentSize, style.logicalHeight(),
+                         constraintSpace, contentContribution);
+  Length maxLength = style.logicalMaxHeight();
+  if (!maxLength.isMaxSizeNone()) {
+    LayoutUnit max = resolveBlockLength(LengthResolveType::MaxSize, maxLength,
+                                        constraintSpace, contentContribution);
+    extent = std::min(extent, max);
+  }
+  LayoutUnit min =
+      resolveBlockLength(LengthResolveType::MinSize, style.logicalMinHeight(),
+                         constraintSpace, contentContribution);
+  extent = std::max(extent, min);
+  if (style.boxSizing() == BoxSizingContentBox) {
+    // TODO(layout-ng): Compute border/padding size and add it
+  }
+  return extent;
+}
+
+}  // namespace blink