Fix Android text size on displays with a different density

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/FabricUIManager.java

@@ -21,6 +21,7 @@
 import android.annotation.SuppressLint;
 import android.content.Context;
 import android.graphics.Point;
+import android.util.DisplayMetrics;
 import android.os.SystemClock;
 import android.view.View;
 import android.view.accessibility.AccessibilityEvent;
@@ -105,6 +106,7 @@
 import java.util.Map;
 import java.util.Queue;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.CopyOnWriteArrayList;
 
@@ -185,6 +187,13 @@ public class FabricUIManager
 
   private final TextEffectRegistry mTextEffectRegistry = new TextEffectRegistry();
 
+  /**
+   * Memoizes the {@link DisplayMetrics} synthesized for each distinct (pointScaleFactor, fontScale)
+   * pair seen during measurement. In practice this holds one entry per display the app has surfaces
+   * on, but text measurement is hot enough that allocating per call is worth avoiding.
+   */
+  private final Map<Long, DisplayMetrics> mSurfaceDisplayMetricsCache = new ConcurrentHashMap<>();
+
   private final BatchEventDispatchedListener mBatchEventDispatchedListener;
 
   private final List<UIManagerListener> mListeners = new CopyOnWriteArrayList<>();
@@ -550,21 +559,52 @@ private NativeArray measureLines(
       ReadableMapBuffer attributedString,
       ReadableMapBuffer paragraphAttributes,
       float width,
-      float height) {
+      float height,
+      float pointScaleFactor,
+      float fontScale) {
     ViewManager textViewManager = mViewManagerRegistry.get(ReactTextViewManager.REACT_CLASS);
+    DisplayMetrics metrics = surfaceDisplayMetrics(pointScaleFactor, fontScale);
 
     return (NativeArray)
         TextLayoutManager.measureLines(
             mReactApplicationContext.getAssets(),
             ReactTypefaceUtils.getFontWeightAdjustment(mReactApplicationContext),
             attributedString,
             paragraphAttributes,
-            PixelUtil.toPixelFromDIP(width),
-            PixelUtil.toPixelFromDIP(height),
+            PixelUtil.toPixelFromDIP(width, metrics),
+            PixelUtil.toPixelFromDIP(height, metrics),
             textViewManager instanceof ReactTextViewManagerCallback
                 ? (ReactTextViewManagerCallback) textViewManager
                 : null,
-            mTextEffectRegistry);
+            mTextEffectRegistry,
+            metrics);
+  }
+
+  /**
+   * The {@link DisplayMetrics} text should be measured against for the surface currently being laid
+   * out.
+   *
+   * <p>{@code pointScaleFactor} and {@code fontScale} originate from the surface's {@code
+   * LayoutContext}, which {@link com.facebook.react.runtime.ReactSurfaceImpl} derives from the
+   * Activity's resources — i.e. from the display the surface is actually on. {@link
+   * DisplayMetricsHolder} in contrast always describes the device's primary display, so on a
+   * secondary display (Samsung DeX, desktop mode, an external monitor, a freeform window) the two
+   * disagree and text is measured at one scale but mounted at another.
+   */
+  private DisplayMetrics surfaceDisplayMetrics(float pointScaleFactor, float fontScale) {
+    if (!ReactNativeFeatureFlags.enablePerSurfaceTextScaleAndroid()) {
+      return DisplayMetricsHolder.getScreenDisplayMetrics();
+    }
+
+    long key = (((long) Float.floatToRawIntBits(pointScaleFactor)) << 32) | (Float.floatToRawIntBits(fontScale) & 0xFFFFFFFFL);
+    DisplayMetrics cached = mSurfaceDisplayMetricsCache.get(key);
+    if (cached != null) {
+      return cached;
+    }
+
+    DisplayMetrics metrics = PixelUtil.displayMetricsFor(pointScaleFactor, fontScale);
+    DisplayMetrics existing = mSurfaceDisplayMetricsCache.putIfAbsent(key, metrics);
+    return existing != null ? existing : metrics;
   }
 
   public @Nullable Integer getColor(int surfaceId, String[] resourcePaths) {
@@ -639,24 +679,28 @@ public long measureText(
       float maxWidth,
       float minHeight,
       float maxHeight,
-      @Nullable float[] attachmentsPositions) {
+      @Nullable float[] attachmentsPositions,
+      float pointScaleFactor,
+      float fontScale) {
 
     ViewManager textViewManager = mViewManagerRegistry.get(ReactTextViewManager.REACT_CLASS);
+    DisplayMetrics metrics = surfaceDisplayMetrics(pointScaleFactor, fontScale);
 
     return TextLayoutManager.measureText(
         mReactApplicationContext.getAssets(),
         ReactTypefaceUtils.getFontWeightAdjustment(mReactApplicationContext),
         attributedString,
         paragraphAttributes,
-        getYogaSize(minWidth, maxWidth),
+        getYogaSize(minWidth, maxWidth, metrics),
         getYogaMeasureMode(minWidth, maxWidth),
-        getYogaSize(minHeight, maxHeight),
+        getYogaSize(minHeight, maxHeight, metrics),
         getYogaMeasureMode(minHeight, maxHeight),
         textViewManager instanceof ReactTextViewManagerCallback
             ? (ReactTextViewManagerCallback) textViewManager
             : null,
         attachmentsPositions,
-        mTextEffectRegistry);
+        mTextEffectRegistry,
+        metrics);
   }
 
   @AnyThread
@@ -668,22 +712,26 @@ public PreparedLayout prepareTextLayout(
       float minWidth,
       float maxWidth,
       float minHeight,
-      float maxHeight) {
+      float maxHeight,
+      float pointScaleFactor,
+      float fontScale) {
     ViewManager textViewManager = mViewManagerRegistry.get(ReactTextViewManager.REACT_CLASS);
+    DisplayMetrics metrics = surfaceDisplayMetrics(pointScaleFactor, fontScale);
 
     return TextLayoutManager.createPreparedLayout(
         mReactApplicationContext.getAssets(),
         ReactTypefaceUtils.getFontWeightAdjustment(mReactApplicationContext),
         attributedString,
         paragraphAttributes,
-        getYogaSize(minWidth, maxWidth),
+        getYogaSize(minWidth, maxWidth, metrics),
         getYogaMeasureMode(minWidth, maxWidth),
-        getYogaSize(minHeight, maxHeight),
+        getYogaSize(minHeight, maxHeight, metrics),
         getYogaMeasureMode(minHeight, maxHeight),
         textViewManager instanceof ReactTextViewManagerCallback
             ? (ReactTextViewManagerCallback) textViewManager
             : null,
-        mTextEffectRegistry);
+        mTextEffectRegistry,
+        metrics);
   }
 
   @AnyThread
@@ -697,7 +745,8 @@ public PreparedLayout reusePreparedLayoutWithNewReactTags(
         preparedLayout.getVerticalOffset(),
         reactTags,
         preparedLayout.getTextBreakStrategy(),
-        preparedLayout.getJustificationMode());
+        preparedLayout.getJustificationMode(),
+        preparedLayout.getDisplayMetrics());
   }
 
   @AnyThread
@@ -709,11 +758,15 @@ public float[] measurePreparedLayout(
       float maxWidth,
       float minHeight,
       float maxHeight) {
+    // A prepared layout is in physical pixels of the display it was laid out on, so its constraints
+    // have to be converted with the metrics it was prepared with rather than the primary display's.
+    DisplayMetrics metrics = preparedLayout.getDisplayMetrics();
+
     return TextLayoutManager.measurePreparedLayout(
         preparedLayout,
-        getYogaSize(minWidth, maxWidth),
+        getYogaSize(minWidth, maxWidth, metrics),
         getYogaMeasureMode(minWidth, maxWidth),
-        getYogaSize(minHeight, maxHeight),
+        getYogaSize(minHeight, maxHeight, metrics),
         getYogaMeasureMode(minHeight, maxHeight));
   }
 

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/LayoutMetricsConversions.kt

@@ -7,6 +7,7 @@
 
 package com.facebook.react.fabric.mounting
 
+import android.util.DisplayMetrics
 import android.view.View.MeasureSpec
 import com.facebook.react.uimanager.PixelUtil.dpToPx
 import com.facebook.yoga.YogaMeasureMode
@@ -40,6 +41,20 @@ internal interface LayoutMetricsConversions {
           maxSize.dpToPx()
         }
 
+    /**
+     * Same as [getYogaSize], but converts using [metrics] rather than the process-wide
+     * [com.facebook.react.uimanager.DisplayMetricsHolder], which always tracks the primary display.
+     */
+    @JvmStatic
+    fun getYogaSize(minSize: Float, maxSize: Float, metrics: DisplayMetrics): Float =
+        if (minSize == maxSize) {
+          maxSize.dpToPx(metrics)
+        } else if (maxSize.isInfinite()) {
+          Float.POSITIVE_INFINITY
+        } else {
+          maxSize.dpToPx(metrics)
+        }
+
     @JvmStatic
     fun getYogaMeasureMode(minSize: Float, maxSize: Float): YogaMeasureMode =
         if (minSize == maxSize) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlags.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<2fc347cdb33327437d29e5fd91e24011>>
+ * @generated SignedSource<<9d2dd4be9427f8e3bc4ffdcb61f23c76>>
  */
 
 /**
@@ -276,6 +276,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun enableNativeCSSParsing(): Boolean = accessor.enableNativeCSSParsing()
 
+  /**
+   * Measures and mounts text using the density of the display the surface is on, instead of the process-wide DisplayMetricsHolder (which always tracks the primary display).
+   */
+  @JvmStatic
+  public fun enablePerSurfaceTextScaleAndroid(): Boolean = accessor.enablePerSurfaceTextScaleAndroid()
+
   /**
    * Enables caching text layout artifacts for later reuse
    */

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<a506d2515fce404e19bd61099cc60117>>
+ * @generated SignedSource<<f2921974a2554c78a6a12f833e4cf5cb>>
  */
 
 /**
@@ -61,6 +61,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var enableMountingCoordinatorPullModelAndroidCache: Boolean? = null
   private var enableMutationObserverByDefaultCache: Boolean? = null
   private var enableNativeCSSParsingCache: Boolean? = null
+  private var enablePerSurfaceTextScaleAndroidCache: Boolean? = null
   private var enablePreparedTextLayoutCache: Boolean? = null
   private var enablePropsUpdateReconciliationAndroidCache: Boolean? = null
   private var enableRuntimeSchedulerQueueClearingOnErrorCache: Boolean? = null
@@ -477,6 +478,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun enablePerSurfaceTextScaleAndroid(): Boolean {
+    var cached = enablePerSurfaceTextScaleAndroidCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.enablePerSurfaceTextScaleAndroid()
+      enablePerSurfaceTextScaleAndroidCache = cached
+    }
+    return cached
+  }
+
   override fun enablePreparedTextLayout(): Boolean {
     var cached = enablePreparedTextLayoutCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxInterop.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<1ef72233f02973021b83bd2e2aa1f69b>>
+ * @generated SignedSource<<6f38ac16b33db913b5ffbde151c2fc0c>>
  */
 
 /**
@@ -110,6 +110,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun enableNativeCSSParsing(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun enablePerSurfaceTextScaleAndroid(): Boolean
+
   @DoNotStrip @JvmStatic public external fun enablePreparedTextLayout(): Boolean
 
   @DoNotStrip @JvmStatic public external fun enablePropsUpdateReconciliationAndroid(): Boolean

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<eb9958ddc04dd1cd8d1add366f5f7741>>
+ * @generated SignedSource<<53359f6086cfbdae9c9cfec04548b6ff>>
  */
 
 /**
@@ -105,6 +105,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun enableNativeCSSParsing(): Boolean = false
 
+  override fun enablePerSurfaceTextScaleAndroid(): Boolean = false
+
   override fun enablePreparedTextLayout(): Boolean = false
 
   override fun enablePropsUpdateReconciliationAndroid(): Boolean = false

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsLocalAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<9ae32c46a5a6310ef96eb91c9ea5b12e>>
+ * @generated SignedSource<<911cf02f383e704acc90b8302041d5a1>>
  */
 
 /**
@@ -65,6 +65,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var enableMountingCoordinatorPullModelAndroidCache: Boolean? = null
   private var enableMutationObserverByDefaultCache: Boolean? = null
   private var enableNativeCSSParsingCache: Boolean? = null
+  private var enablePerSurfaceTextScaleAndroidCache: Boolean? = null
   private var enablePreparedTextLayoutCache: Boolean? = null
   private var enablePropsUpdateReconciliationAndroidCache: Boolean? = null
   private var enableRuntimeSchedulerQueueClearingOnErrorCache: Boolean? = null
@@ -522,6 +523,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun enablePerSurfaceTextScaleAndroid(): Boolean {
+    var cached = enablePerSurfaceTextScaleAndroidCache
+    if (cached == null) {
+      cached = currentProvider.enablePerSurfaceTextScaleAndroid()
+      accessedFeatureFlags.add("enablePerSurfaceTextScaleAndroid")
+      enablePerSurfaceTextScaleAndroidCache = cached
+    }
+    return cached
+  }
+
   override fun enablePreparedTextLayout(): Boolean {
     var cached = enablePreparedTextLayoutCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsProvider.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<1a1d47f2d85404c776e55db40f7dbc6e>>
+ * @generated SignedSource<<0bffb447de4a420f3df5d2b43d62be21>>
  */
 
 /**
@@ -105,6 +105,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun enableNativeCSSParsing(): Boolean
 
+  @DoNotStrip public fun enablePerSurfaceTextScaleAndroid(): Boolean
+
   @DoNotStrip public fun enablePreparedTextLayout(): Boolean
 
   @DoNotStrip public fun enablePropsUpdateReconciliationAndroid(): Boolean