Adaptive Display: what does UiScaleFactor change for an app, and can it be set on the Virtual Device?

Vega Open Beta Q&A
1

App Name: Dice Chess TV
App Link on Amazon Appstore: not published yet (in Live App Testing)
SDK Version: v0.24 (0.24.12112)
React Native Version: RN 0.83

Hi! The developer news of August 17 says Adaptive Display is now available on Vega devices, making text and menus bigger, and suggests checking how app layouts hold up. We would like to check ours before release. Our Fire TV Stick 4K Select has been on order since September 22, but it is not sold in Latvia yet and has not arrived, so for now we only have the Vega Virtual Device (OS 1.2).

What we found on the Virtual Device:

  • Its Settings has only Account Settings, with no Accessibility or Display section.
  • vdcm get com.amazon.devconf/system/accessibility/UiScaleFactor returns '1'. We guess this is the Adaptive Display scale, but could not find it documented.
  • vdcm set on that key fails with No permission for operation, from vega device shell (uid app_user). The command from the WebView accessibility guide, vdcm set "com.amazon.devconf/system/accessibility/VoiceViewEnabled" "ENABLED", fails the same way.
  • a11y-tv-util settings list fails with Error obtaining user profile object.

Questions:

  1. Is UiScaleFactor the setting behind Adaptive Display, and which values can it take?
  2. What does it change for a React Native for Vega app: fontScale (so Text grows through allowFontScaling), the dp-to-pixel scale and window size, or does the system zoom the whole picture?
  3. Is there a supported way to turn it on, or to set a font scale, on the Virtual Device for testing?

Thanks!

4

Hi @Fortemate,

Thanks for the detailed write-up - here’s where things stand:

  1. Is UiScaleFactor the Adaptive Display setting, and what values does it take?
    Let me check with the team and get back to you on this. In the meantime, the signal to react to in your app is fontScale (see #2) - I’d build against that rather than reading that config key directly.

  2. What does it change for your app?
    Vega keeps two things separate: the display scale factor (dp→pixel mapping / window size, i.e. scale) and accessibility font scaling (fontScale). Per the Density-Independent Pixels guide ( Density-Independent Pixels - Amazon Vega Docs ): “dp rendering doesn’t replace accessibility font scaling. Keep using React Native text APIs and fontScale for user-selected text size.”
    So read fontScale via Dimensions.get(‘window’).fontScale, useWindowDimensions().fontScale, or PixelRatio.getFontScale() ( PixelRatio - Amazon Vega Docs ). The Text component scales automatically since allowFontScaling defaults to true( Text - Amazon Vega Docs ) (bound it with maxFontSizeMultiplier). It’s a text-size preference independent of the dp scale factor - so design layouts to tolerate larger text (let it reflow, avoid fixed-height/clipping containers).

  3. Setting it on the Virtual Device?
    Your results are expected, not a misconfiguration. vdcm set fails because setting accessibility values is privilege-gated - per the 0.24 Release Notes ( Vega SDK Release Notes - Amazon Vega Docs ): “Reading settings is open to apps. Setting accessibility values is gated by a runtime privilege.” There’s no documented way to toggle Adaptive Display / font scale on the current VVD, and it doesn’t expose an Accessibility settings section.

Until your Fire TV Stick 4K Select arrives: build your app to read fontScale and reflow
(testable in code on the VVD), then do final large-text validation on the physical device via
Settings → Accessibility → Adaptive Display.

Best,
Aishwarya