Fabric: UIManager::getRelativeLayoutMetrics

Summary: This method is underlying infra for all `measure`-like methods exposed to JavaScript.

Reviewed By: mdvacca

Differential Revision: D13036553

fbshipit-source-id: cb5135f1db97ec8144b31a24ee4fb9f5d61f0df1

ReactCommon/fabric/uimanager/ShadowTree.h

@@ -77,6 +77,11 @@ class ShadowTree final {
    */
   bool complete(const SharedShadowNodeUnsharedList &rootChildNodes) const;
 
+  /*
+   * Returns a root shadow node that represents the last committed three.
+   */
+  SharedRootShadowNode getRootShadowNode() const;
+
 #pragma mark - Delegate
 
   /*
@@ -105,11 +110,6 @@ class ShadowTree final {
   void toggleEventEmitters(const ShadowViewMutationList &mutations) const;
   void emitLayoutEvents(const ShadowViewMutationList &mutations) const;
 
-  /*
-   * Return `rootShadowNodeMutex_` protected by `commitMutex_`.
-   */
-  SharedRootShadowNode getRootShadowNode() const;
-
   const SurfaceId surfaceId_;
   mutable SharedRootShadowNode rootShadowNode_; // Protected by `commitMutex_`.
   ShadowTreeDelegate const *delegate_;

ReactCommon/fabric/uimanager/UIManager.cpp

@@ -67,6 +67,29 @@ void UIManager::completeSurface(
   }
 }
 
+LayoutMetrics UIManager::getRelativeLayoutMetrics(
+    const ShadowNode &shadowNode,
+    const ShadowNode *ancestorShadowNode) const {
+  if (!ancestorShadowNode) {
+    shadowTreeRegistry_->get(
+        shadowNode.getRootTag(), [&](const ShadowTree &shadowTree) {
+          ancestorShadowNode = shadowTree.getRootShadowNode().get();
+        });
+  }
+
+  auto layoutableShadowNode =
+      dynamic_cast<const LayoutableShadowNode *>(&shadowNode);
+  auto layoutableAncestorShadowNode =
+      dynamic_cast<const LayoutableShadowNode *>(ancestorShadowNode);
+
+  if (!layoutableShadowNode || !layoutableAncestorShadowNode) {
+    return EmptyLayoutMetrics;
+  }
+
+  return layoutableShadowNode->getRelativeLayoutMetrics(
+      *layoutableAncestorShadowNode);
+}
+
 void UIManager::setShadowTreeRegistry(ShadowTreeRegistry *shadowTreeRegistry) {
   shadowTreeRegistry_ = shadowTreeRegistry;
 }

ReactCommon/fabric/uimanager/UIManager.h

@@ -52,6 +52,15 @@ class UIManager {
       SurfaceId surfaceId,
       const SharedShadowNodeUnsharedList &rootChildren) const;
 
+  /*
+   * Returns layout metrics of given `shadowNode` relative to
+   * `ancestorShadowNode` (relative to the root node in case if provided
+   * `ancestorShadowNode` is nullptr).
+   */
+  LayoutMetrics getRelativeLayoutMetrics(
+      const ShadowNode &shadowNode,
+      const ShadowNode *ancestorShadowNode) const;
+
   ShadowTreeRegistry *shadowTreeRegistry_;
   SharedComponentDescriptorRegistry componentDescriptorRegistry_;
   UIManagerDelegate *delegate_;