From 23f1b030577b8a98d886c6ca2fa7c9bb5c319f96 Mon Sep 17 00:00:00 2001
From: Collin Schneide <27441618+FaithfulAudio@users.noreply.github.com>
Date: Sat, 18 Jul 2026 19:53:39 +0800
Subject: [PATCH 1/2] fix(textinput): correct placeholder layout constraints
 (px vs DIP) and no-op NaN fontSize guard

Forward-port of #16303 (0.83-stable) to main.

CreatePlaceholderLayout fed m_imgWidth/m_imgHeight - which are physical
pixels (frame * pointScaleFactor) - into LayoutConstraints, which are
expressed in DIPs. The placeholder was laid out in a box pointScaleFactor
times too large, so it measured and positioned at a different height than
the typed text. Divide by pointScaleFactor.

The NaN fontSize guard was also a no-op: it evaluated
defaultTextAttributes().fontSize as a discarded expression statement
instead of assigning it, so a placeholder with no fontSize never picked
up the default.
---
 .../TextInput/WindowsTextInputComponentView.cpp        | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/vnext/Microsoft.ReactNative/Fabric/Composition/TextInput/WindowsTextInputComponentView.cpp b/vnext/Microsoft.ReactNative/Fabric/Composition/TextInput/WindowsTextInputComponentView.cpp
index 91ae1551daf..a8af925e960 100644
--- a/vnext/Microsoft.ReactNative/Fabric/Composition/TextInput/WindowsTextInputComponentView.cpp
+++ b/vnext/Microsoft.ReactNative/Fabric/Composition/TextInput/WindowsTextInputComponentView.cpp
@@ -1743,7 +1743,7 @@ winrt::com_ptr<::IDWriteTextLayout> WindowsTextInputComponentView::CreatePlaceho
   const auto &props = windowsTextInputProps();
   facebook::react::TextAttributes textAttributes = props.textAttributes;
   if (std::isnan(props.textAttributes.fontSize)) {
-    facebook::react::TextAttributes::defaultTextAttributes().fontSize;
+    textAttributes.fontSize = facebook::react::TextAttributes::defaultTextAttributes().fontSize;
   }
   textAttributes.fontSizeMultiplier = m_fontSizeMultiplier;
   fragment1.string = props.placeholder;
@@ -1751,8 +1751,12 @@ winrt::com_ptr<::IDWriteTextLayout> WindowsTextInputComponentView::CreatePlaceho
   attributedString.appendFragment(std::move(fragment1));
 
   facebook::react::LayoutConstraints constraints;
-  constraints.maximumSize.width = static_cast<FLOAT>(m_imgWidth);
-  constraints.maximumSize.height = static_cast<FLOAT>(m_imgHeight);
+  // m_imgWidth/m_imgHeight are physical pixels (frame * pointScaleFactor), but
+  // LayoutConstraints are expressed in DIPs. Feeding physical px laid the
+  // placeholder out in a box pointScaleFactor x too large, so the placeholder was
+  // measured/positioned at a different height than the typed text. Convert to DIPs.
+  constraints.maximumSize.width = static_cast<FLOAT>(m_imgWidth) / m_layoutMetrics.pointScaleFactor;
+  constraints.maximumSize.height = static_cast<FLOAT>(m_imgHeight) / m_layoutMetrics.pointScaleFactor;
 
   facebook::react::WindowsTextLayoutManager::GetTextLayout(
       facebook::react::AttributedStringBox(attributedString), {} /*TODO*/, constraints, textLayout);

From c8537041ba6ccdcd1e76840472835dc1551aed42 Mon Sep 17 00:00:00 2001
From: Collin Schneide <27441618+FaithfulAudio@users.noreply.github.com>
Date: Sat, 18 Jul 2026 19:53:41 +0800
Subject: [PATCH 2/2] add beachball change file

---
 ...eact-native-windows-fix-textinput-placeholder-main.json | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 change/react-native-windows-fix-textinput-placeholder-main.json

diff --git a/change/react-native-windows-fix-textinput-placeholder-main.json b/change/react-native-windows-fix-textinput-placeholder-main.json
new file mode 100644
index 00000000000..b759d12c2d5
--- /dev/null
+++ b/change/react-native-windows-fix-textinput-placeholder-main.json
@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "Fix placeholder layout constraints fed physical px instead of DIPs; fix no-op NaN fontSize guard in CreatePlaceholderLayout",
+  "packageName": "react-native-windows",
+  "email": "collindanielschneide@gmail.com",
+  "dependentChangeType": "patch"
+}