[Android] Dimensions.get('screen').scale reports primary display density on secondary displays, breaking Fabric layout

Description

On Android, when a React Native activity runs on a secondary display (Samsung DeX, external monitor via desktop mode, ChromeOS desktop windowing, virtual/emulator display via am start --display N), the activity renders at the wrong scale. Content is laid out as if the surface were larger than the activity window, the visible region is a fraction of the window with the rest left black, and text rendering is sub-pixel-blurry.

Dimensions.get('window') and useWindowDimensions() report the activity's actual display correctly. Only Dimensions.get('screen').scale is wrong: it reports the device's primary-display density regardless of which display the activity is on.

window: { width: 1600, height: 720, scale: 1.5 }   ← matches the activity's display
screen: { width: 800,  height: 360, scale: 3   }   ← primary display's scale

Steps to reproduce

1. Boot a phone-form-factor AVD (verified on Pixel 9 Pro, API 36).
2. Attach a virtual secondary display at a different density than the primary (Pixel 9 Pro is 3.0×, 240dpi on the secondary is enough):

   adb emu multidisplay add 1 2400 1080 240 0
   

3. Install the reproducer, start Metro, launch onto the secondary display:

   cd ReproducerApp && npm install && npm run android && npm start &
   adb shell am force-stop com.reproducerapp
   adb shell am start -n com.reproducerapp/.MainActivity --display 3
   

Expected: screen.scale === window.scale when the activity is on a single display.

Actual: screen.scale is the primary's density; the React surface lays out at the primary's scale into a window that doesn't have that scale.

React Native Version

0.85.3

Affected Platforms

Runtime - Android

Areas

Fabric - The New Renderer, Bridgeless - The New Initialization Flow

Output of npx @react-native-community/cli info

System:
  OS: macOS 26.3.1
  CPU: (14) arm64 Apple M4 Pro
  Memory: 506.70 MB / 48.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 24.13.0
    path: /Users/douwe/.nvm/versions/node/v24.13.0/bin/node
  Yarn:
    version: 1.22.22
    path: /opt/homebrew/bin/yarn
  npm:
    version: 11.6.2
    path: /Users/douwe/.nvm/versions/node/v24.13.0/bin/npm
  Watchman:
    version: 2025.05.26.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  Android SDK:
    API Levels:
      - "31"
      - "32"
      - "33"
      - "34"
      - "35"
      - "36"
    Build Tools:
      - 30.0.3
      - 34.0.0
      - 35.0.0
      - 36.0.0
      - 36.1.0
    Android NDK: Not Found
IDEs:
  Android Studio: 2025.3 AI-253.29346.138.2531.14876573
Languages:
  Java:
    version: 21.0.10
    path: /usr/bin/javac
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.85.3
    wanted: 0.85.3
Android:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

adb logcat from the reproducer on the secondary display (2400x1080 @ 240dpi):

ReactNativeJS: '[repro] Dimensions.initial', '{"window":{"width":1600,"height":720,"scale":1.5,"fontScale":1},"screen":{"width":800,"height":360,"scale":3,"fontScale":1}}'

MANDATORY Reproducer

https://github.com/DouweBos/rn-secondary-display-repro

Screenshots and Videos

2400×1080 @ 240dpi secondary — cut off text, surface laid out at the wrong density:

Same with an app-side workaround that overwrites DisplayMetricsHolder with the activity's actual metrics — screen.scale matches window.scale, text renders crisply:

---

Related: #55659.

Commencez par le rn-secondary-display-repro obligatoire et reproduisez l'écart à l'aide des commandes adb emu et am start indiquées. Suivez le chemin Android qui alimente DisplayMetricsHolder et comparez ses métriques avec les métriques d'affichage de l'activité. C'est terminé lorsque Dimensions.get('screen').scale correspond à window.scale sur un seul écran secondaire et que la surface Fabric est rendue avec la densité correcte.