Fabric: LayoutableShadowNode::getRelativeLayoutMetrics()

Summary:
The generic method that returns relative (to some specified node) layout metrics.
We need this as a building block to implement `UIManager.measure*()` methods family.

Reviewed By: mdvacca

Differential Revision: D12932549

fbshipit-source-id: 79064551d32b0cd40e72dc87d0ed194e3779ba29

ReactCommon/fabric/core/layout/LayoutableShadowNode.cpp

@@ -10,6 +10,7 @@
 #include <react/core/LayoutConstraints.h>
 #include <react/core/LayoutContext.h>
 #include <react/core/LayoutMetrics.h>
+#include <react/core/ShadowNode.h>
 #include <react/debug/DebugStringConvertibleItem.h>
 #include <react/graphics/conversions.h>
 
@@ -35,6 +36,35 @@ bool LayoutableShadowNode::LayoutableShadowNode::isLayoutOnly() const {
   return false;
 }
 
+LayoutMetrics LayoutableShadowNode::getRelativeLayoutMetrics(
+    const LayoutableShadowNode &ancestorLayoutableShadowNode) const {
+  std::vector<std::reference_wrapper<const ShadowNode>> ancestors;
+
+  auto &ancestorShadowNode =
+      dynamic_cast<const ShadowNode &>(ancestorLayoutableShadowNode);
+  auto &shadowNode = dynamic_cast<const ShadowNode &>(*this);
+
+  if (!shadowNode.constructAncestorPath(ancestorShadowNode, ancestors)) {
+    return EmptyLayoutMetrics;
+  }
+
+  auto layoutMetrics = getLayoutMetrics();
+
+  for (const auto &currentShadowNode : ancestors) {
+    auto layoutableCurrentShadowNode =
+        dynamic_cast<const LayoutableShadowNode *>(&currentShadowNode.get());
+
+    if (!layoutableCurrentShadowNode) {
+      return EmptyLayoutMetrics;
+    }
+
+    layoutMetrics.frame.origin +=
+        layoutableCurrentShadowNode->getLayoutMetrics().frame.origin;
+  }
+
+  return layoutMetrics;
+}
+
 void LayoutableShadowNode::cleanLayout() {
   isLayoutClean_ = true;
 }

ReactCommon/fabric/core/layout/LayoutableShadowNode.h

@@ -59,6 +59,12 @@ class LayoutableShadowNode : public virtual Sealable {
    */
   virtual bool isLayoutOnly() const;
 
+  /*
+   * Returns layout metrics relatively to the given ancestor node.
+   */
+  LayoutMetrics getRelativeLayoutMetrics(
+      const LayoutableShadowNode &ancestorLayoutableShadowNode) const;
+
  protected:
   /*
    * Clean or Dirty layout state: