Implement relative utilities

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

Index: third_party/WebKit/Source/core/layout/ng/ng_relative_utils.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_relative_utils.cc b/third_party/WebKit/Source/core/layout/ng/ng_relative_utils.cc
new file mode 100644
index 0000000000000000000000000000000000000000..56fd109bd7b18116bacba34c5f1ed73e738ea050
--- /dev/null
+++ b/third_party/WebKit/Source/core/layout/ng/ng_relative_utils.cc
@@ -0,0 +1,88 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.

[ikilpatrick, 2017/03/16 19:08:36]

2017

[atotic, 2017/03/20 17:31:45]

done

+// 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_relative_utils.h"
+
+#include "core/layout/ng/geometry/ng_logical_offset.h"
+#include "core/style/ComputedStyle.h"
+#include "platform/LengthFunctions.h"
+#include "wtf/Optional.h"
+
+namespace blink {
+
+// Returns child's relative position wrt containing fragment.
+NGLogicalOffset ComputeRelativeOffset(const ComputedStyle& child_style,
+                                      NGWritingMode container_writing_mode,
+                                      TextDirection container_direction,
+                                      NGLogicalSize container_size) {
+  NGLogicalOffset offset;
+  bool is_horizontal =
+      container_writing_mode == NGWritingMode::kHorizontalTopBottom;
+
+  Optional<LayoutUnit> left, right, top, bottom;
+
+  if (is_horizontal) {
+    if (!child_style.left().isAuto())
+      left = valueForLength(child_style.left(), container_size.inline_size);

[ikilpatrick, 2017/03/16 19:08:36]

would it be easier to just convert the container_size to physical and not have
the above if (is_horizontal) ?

[atotic, 2017/03/20 17:31:45]

done. Thanks.

+    if (!child_style.right().isAuto())
+      right = valueForLength(child_style.right(), container_size.inline_size);
+    if (!child_style.top().isAuto())
+      top = valueForLength(child_style.top(), container_size.block_size);
+    if (!child_style.bottom().isAuto())
+      bottom = valueForLength(child_style.bottom(), container_size.block_size);
+  } else {
+    if (!child_style.left().isAuto())
+      left = valueForLength(child_style.left(), container_size.block_size);
+    if (!child_style.right().isAuto())
+      right = valueForLength(child_style.right(), container_size.block_size);
+    if (!child_style.top().isAuto())
+      top = valueForLength(child_style.top(), container_size.inline_size);
+    if (!child_style.bottom().isAuto())
+      bottom = valueForLength(child_style.bottom(), container_size.inline_size);
+  }
+
+  // Implements confict resolution rules from spec:
+  // https://www.w3.org/TR/css-position-3/#rel-pos
+  if (!left && !right) {
+    left = LayoutUnit();
+    right = LayoutUnit();
+  }
+  if (!left)
+    left = -right.value();
+  if (!right)
+    right = -left.value();
+  if (!top && !bottom) {
+    top = LayoutUnit();
+    bottom = LayoutUnit();
+  }
+  if (!top)
+    top = -bottom.value();
+  if (!bottom)
+    bottom = -top.value();
+
+  bool is_ltr = container_direction == TextDirection::kLtr;
+
+  switch (container_writing_mode) {
+    case kHorizontalTopBottom:
+      offset.inline_offset = is_ltr ? left.value() : right.value();
+      offset.block_offset = top.value();
+      break;
+    case kVerticalRightLeft:
+    case kSidewaysRightLeft:
+      offset.inline_offset = is_ltr ? top.value() : bottom.value();
+      offset.block_offset = right.value();
+      break;
+    case kVerticalLeftRight:
+      offset.inline_offset = is_ltr ? top.value() : bottom.value();
+      offset.block_offset = left.value();
+      break;
+    case kSidewaysLeftRight:
+      offset.inline_offset = is_ltr ? bottom.value() : top.value();
+      offset.block_offset = left.value();
+      break;
+  }
+  return offset;
+}
+
+}  // namespace blink