From 7eee607f952217b46c1c0d717bd3c1509f679707 Mon Sep 17 00:00:00 2001
From: Samuel Newman <mozzius@protonmail.com>
Date: Thu, 15 Oct 2026 12:50:00 +0300
Subject: [PATCH] Only dirty Yoga nodes in setSize/setPositionType when the
 value changes

Component descriptors call these from adopt(), which runs on every clone.
Dirtying unconditionally made every commit under such a node (e.g. a
ModalHostView) re-run layout and pixel-grid rounding over the whole surface.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../view/YogaLayoutableShadowNode.cpp         | 21 +++++--
 .../components/view/tests/ViewTest.cpp        | 57 +++++++++++++++++++
 2 files changed, 74 insertions(+), 4 deletions(-)

diff --git a/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp b/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp
index fb7c6e4ffe87..f7085e2a0795 100644
--- a/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp
+++ b/packages/react-native/ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp
@@ -596,11 +596,20 @@ YogaLayoutableShadowNode& YogaLayoutableShadowNode::cloneChildInPlace(
 void YogaLayoutableShadowNode::setSize(Size size) const {
   ensureUnsealed();
 
+  auto width = yoga::StyleSizeLength::points(size.width);
+  auto height = yoga::StyleSizeLength::points(size.height);
+
+  // Component descriptors call this from `adopt`, which runs on every clone.
+  // Dirtying the node when nothing changed would make every commit that clones
+  // it re-run layout over the whole tree.
   auto style = yogaNode_.style();
-  style.setDimension(
-      yoga::Dimension::Width, yoga::StyleSizeLength::points(size.width));
-  style.setDimension(
-      yoga::Dimension::Height, yoga::StyleSizeLength::points(size.height));
+  if (width == style.dimension(yoga::Dimension::Width) &&
+      height == style.dimension(yoga::Dimension::Height)) {
+    return;
+  }
+
+  style.setDimension(yoga::Dimension::Width, width);
+  style.setDimension(yoga::Dimension::Height, height);
   yogaNode_.setStyle(style);
   yogaNode_.setDirty(true);
 }
@@ -635,6 +644,10 @@ void YogaLayoutableShadowNode::setPositionType(
   ensureUnsealed();
 
   auto style = yogaNode_.style();
+  if (style.positionType() == yoga::scopedEnum(positionType)) {
+    return;
+  }
+
   style.setPositionType(yoga::scopedEnum(positionType));
   yogaNode_.setStyle(style);
   yogaNode_.setDirty(true);
diff --git a/packages/react-native/ReactCommon/react/renderer/components/view/tests/ViewTest.cpp b/packages/react-native/ReactCommon/react/renderer/components/view/tests/ViewTest.cpp
index ee71635f315c..14ff9ea528d2 100644
--- a/packages/react-native/ReactCommon/react/renderer/components/view/tests/ViewTest.cpp
+++ b/packages/react-native/ReactCommon/react/renderer/components/view/tests/ViewTest.cpp
@@ -326,6 +326,63 @@ TEST_F(YogaDirtyFlagTest, showingHiddenNodeMustDirtyItAndLayOutItsChildren) {
   EXPECT_EQ(child->getLayoutMetrics().frame.size.width, 42);
 }
 
+TEST_F(YogaDirtyFlagTest, settingUnchangedSizeMustNotDirtyYogaNode) {
+  /*
+   * Component descriptors call `setSize` from `adopt`, which runs on every
+   * clone. Setting the size a node already has must *not* dirty its Yoga node,
+   * otherwise every commit that clones it re-runs layout.
+   */
+  auto setSize = [](const ShadowNode& oldShadowNode) {
+    auto newShadowNode = oldShadowNode.clone({});
+    static_cast<YogaLayoutableShadowNode&>(*newShadowNode)
+        .setSize({.width = 100, .height = 200});
+    return newShadowNode;
+  };
+
+  auto sizedRootShadowNode =
+      rootShadowNode_->cloneTree(innerShadowNode_->getFamily(), setSize);
+
+  /*
+   * Changing the size *must* dirty the Yoga node.
+   */
+  EXPECT_TRUE(
+      static_cast<RootShadowNode&>(*sizedRootShadowNode).layoutIfNeeded());
+
+  auto newRootShadowNode =
+      sizedRootShadowNode->cloneTree(innerShadowNode_->getFamily(), setSize);
+
+  EXPECT_FALSE(
+      static_cast<RootShadowNode&>(*newRootShadowNode).layoutIfNeeded());
+}
+
+TEST_F(YogaDirtyFlagTest, settingUnchangedPositionTypeMustNotDirtyYogaNode) {
+  /*
+   * Setting the position type a node already has must *not* dirty its Yoga
+   * node.
+   */
+  auto setPositionType = [](const ShadowNode& oldShadowNode) {
+    auto newShadowNode = oldShadowNode.clone({});
+    static_cast<YogaLayoutableShadowNode&>(*newShadowNode)
+        .setPositionType(YGPositionTypeAbsolute);
+    return newShadowNode;
+  };
+
+  auto absoluteRootShadowNode = rootShadowNode_->cloneTree(
+      innerShadowNode_->getFamily(), setPositionType);
+
+  /*
+   * Changing the position type *must* dirty the Yoga node.
+   */
+  EXPECT_TRUE(
+      static_cast<RootShadowNode&>(*absoluteRootShadowNode).layoutIfNeeded());
+
+  auto newRootShadowNode = absoluteRootShadowNode->cloneTree(
+      innerShadowNode_->getFamily(), setPositionType);
+
+  EXPECT_FALSE(
+      static_cast<RootShadowNode&>(*newRootShadowNode).layoutIfNeeded());
+}
+
 TEST_F(YogaDirtyFlagTest, clonedPropsPreserveAspectRatio) {
   ContextContainer contextContainer{};
   PropsParserContext parserContext{-1, contextContainer};