Keep paragraph content and measured layouts across unchanged clones

packages/react-native/ReactCommon/react/renderer/components/text/ParagraphShadowNode.cpp

@@ -59,6 +59,23 @@ ParagraphShadowNode::ParagraphShadowNode(
     const ShadowNodeFragment& fragment)
     : ConcreteViewShadowNode(sourceShadowNode, fragment) {
   initialize();
+  // A revision with neither new props nor new children (e.g. one Yoga cloned
+  // because a sibling changed) renders the same content, so keep the
+  // attributed string and the layouts measured for it instead of rebuilding
+  // and re-measuring them. `getContent` drops both if the layout context they
+  // were built for no longer matches.
+  //
+  // Content with attachments is not kept: they point at the children the
+  // content was built from, and `layout` replaces those children with laid-out
+  // clones, so in a later revision the pointers would outlive the nodes.
+  if (fragment.props == nullptr && fragment.children == nullptr) {
+    const auto& source =
+        static_cast<const ParagraphShadowNode&>(sourceShadowNode);
+    if (source.content_.has_value() && source.content_->attachments.empty()) {
+      content_ = source.content_;
+      measuredLayouts_ = source.measuredLayouts_;
+    }
+  }
 }
 
 bool ParagraphShadowNode::shouldNewRevisionDirtyMeasurement(
@@ -69,19 +86,34 @@ bool ParagraphShadowNode::shouldNewRevisionDirtyMeasurement(
 
 const Content& ParagraphShadowNode::getContent(
     const LayoutContext& layoutContext) const {
+  auto layoutDirection = YGNodeLayoutGetDirection(&yogaNode_) == YGDirectionRTL
+      ? LayoutDirection::RightToLeft
+      : LayoutDirection::LeftToRight;
   if (content_.has_value()) {
-    return content_.value();
+    const auto& baseTextAttributes =
+        content_->attributedString.getBaseTextAttributes();
+    // The content is built from this node's props and children, and it is
+    // only carried over to revisions that have neither new props nor new
+    // children (see the copy constructor). The only other inputs are the
+    // font size multiplier from the layout context and the layout direction
+    // Yoga resolves from the parent, and those can change without new props
+    // or children, so they are the two things to check here.
+    if (baseTextAttributes.fontSizeMultiplier ==
+            layoutContext.fontSizeMultiplier &&
+        baseTextAttributes.layoutDirection == layoutDirection) {
+      return content_.value();
+    }
+    // Carried over from a previous revision, but built for another context.
+    content_.reset();
+    measuredLayouts_.clear();
   }
 
   ensureUnsealed();
 
   auto textAttributes = TextAttributes::defaultTextAttributes();
   textAttributes.fontSizeMultiplier = layoutContext.fontSizeMultiplier;
   textAttributes.apply(getConcreteProps().textAttributes);
-  textAttributes.layoutDirection =
-      YGNodeLayoutGetDirection(&yogaNode_) == YGDirectionRTL
-      ? LayoutDirection::RightToLeft
-      : LayoutDirection::LeftToRight;
+  textAttributes.layoutDirection = layoutDirection;
   auto attributedString = AttributedString{};
   auto attachments = Attachments{};
   buildAttributedString(textAttributes, *this, attributedString, attachments);
@@ -189,7 +221,8 @@ void ParagraphShadowNode::updateStateIfNeeded(const Content& content) {
           textLayoutManager_});
 }
 
-MeasuredPreparedTextLayout* ParagraphShadowNode::findUsableLayout() {
+MeasuredPreparedTextLayout* ParagraphShadowNode::findUsableLayout(
+    Float pointScaleFactor) {
   MeasuredPreparedTextLayout* ret = nullptr;
 
   if constexpr (TextLayoutManagerExtended::supportsPreparedTextLayout()) {
@@ -201,7 +234,8 @@ MeasuredPreparedTextLayout* ParagraphShadowNode::findUsableLayout() {
     // adjusted by a constraint (like min-size).
     auto expectedSize = rawContentSize();
     for (auto& prevLayout : measuredLayouts_) {
-      if (floatEquality(
+      if (prevLayout.pointScaleFactor == pointScaleFactor &&
+          floatEquality(
               prevLayout.measurement.size.width, expectedSize.width) &&
           floatEquality(
               prevLayout.measurement.size.height, expectedSize.height)) {
@@ -230,8 +264,11 @@ Size ParagraphShadowNode::measureContent(
     const LayoutContext& layoutContext,
     const LayoutConstraints& layoutConstraints) const {
   if constexpr (TextLayoutManagerExtended::supportsPreparedTextLayout()) {
+    // Layouts carried over from a previous revision may have been prepared
+    // at another pixel density, which they can't be reused for.
     for (const auto& layout : measuredLayouts_) {
-      if (layout.layoutConstraints == layoutConstraints) {
+      if (layout.layoutConstraints == layoutConstraints &&
+          layout.pointScaleFactor == layoutContext.pointScaleFactor) {
         return layout.measurement.size;
       }
     }
@@ -321,7 +358,7 @@ void ParagraphShadowNode::layout(LayoutContext layoutContext) {
   auto content =
       getContentWithMeasuredAttachments(layoutContext, layoutConstraints);
 
-  auto measuredLayout = findUsableLayout();
+  auto measuredLayout = findUsableLayout(layoutContext.pointScaleFactor);
 
   if constexpr (
       TextLayoutManagerExtended::supportsPreparedTextLayout() &&
@@ -338,7 +375,7 @@ void ParagraphShadowNode::layout(LayoutContext layoutContext) {
       // culled
       if (measuredLayout == nullptr) {
         measureContent(layoutContext, layoutConstraints);
-        measuredLayout = findUsableLayout();
+        measuredLayout = findUsableLayout(layoutContext.pointScaleFactor);
       }
       react_native_assert(measuredLayout);
       updateStateIfNeeded<ParagraphState>(content, *measuredLayout);

packages/react-native/ReactCommon/react/renderer/components/text/ParagraphShadowNode.h

@@ -117,9 +117,10 @@ class ParagraphShadowNode
 
   /**
    * Returns any previously prepared layout, generated for measurement, which
-   * may be used, given the currently assigned layout to the ShadowNode
+   * may be used, given the currently assigned layout to the ShadowNode and
+   * the current pixel density
    */
-  MeasuredPreparedTextLayout *findUsableLayout();
+  MeasuredPreparedTextLayout *findUsableLayout(Float pointScaleFactor);
 
   /**
    * Returns the final measure of the content frame, before layout rounding