title: Live Wallpaper isVisible/onVisibilityChanged not working with Android 9+ App drawer
body: <p>I have observed No visibility change reported by the <em><strong>isVisible()</strong></em> and/or <em><strong>onVisibilityChanged()</strong></em> when a Live Wallpaper is covered by AppsDrawer on an Android 9 phone. I am guessing it's because the Apps Drawer is shown translucent, as you can make out a hint of LWP shown underneath.</p>
  <p>Reason I need to be able to determine when AppsDrawer obscures my LWP is, just as the doc says
  <em><strong>It is very important that a wallpaper only use CPU while it is visible</strong>..</em>
  <a href="https://developer.android.com/reference/android/service/wallpaper/WallpaperService.Engine" rel="nofollow noreferrer">https://developer.android.com/reference/android/service/wallpaper/WallpaperService.Engine</a></p>
  <p>Is there some alternative ways to work out visibility or focus change? not sure LWP really gets a focus</p>