Merge pull request #8 from Brian5647/fix-map-freeze

fix the drawing after coming back from the media menu to navigation app

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarHomeScreen.kt

@@ -83,12 +83,16 @@ fun CarHome() {
     val navigator = LocalCarNavigator.current
     val panel = navigator.sidePanel
 
-    // Coming back to the map from another screen: make sure the nav app is drawing into a live
+    // Leaving the map for another screen: hand the nav app a fresh surface while it's covered, so
-    // surface. The first composition is skipped, since the surface is only just being lent.
+    // it has redrawn by the time the map comes back - a new surface shows black until the app's
+    // next frame. Coming back only replaces one that died meanwhile. Nothing happens before Home
+    // has first been shown, since the surface is only just being lent.
     val onHome = navigator.current == CarScreen.Home
     val seenHome = remember { booleanArrayOf(false) }
     LaunchedEffect(onHome) {
-        if (onHome && seenHome[0]) CarServices.nav.refreshSurface()
+        if (seenHome[0]) {
+            if (onHome) CarServices.nav.replaceDeadSurface() else CarServices.nav.renewSurface()
+        }
         if (onHome) seenHome[0] = true
     }
     val splitScreen = phase == CarMedia.Phase.READY && now.isActive && panel != SidePanel.NONE

gearslip/src/main/java/app/seb3thehacker/gearslip/host/CarAppConnection.kt

@@ -455,31 +455,48 @@ class CarAppConnection(private val context: Context) {
 
     private val _surfaceEpoch = MutableStateFlow(0)
 
-    /** Bumped when the lent surface turns out to be dead, so the stage builds a fresh one. */
+    /** Bumped to throw the lent surface away, so the stage builds a fresh one. */
     val surfaceEpoch: StateFlow<Int> = _surfaceEpoch.asStateFlow()
 
     /**
-     * Lends the app its surface again: called when the map comes back into view. An app that
+     * Lends the app a fresh surface: called as the map goes out of view, so the app has redrawn
-     * draws through its own VirtualDisplay (Organic Maps does) can be left pointing at a surface
+     * on the new one by the time it comes back. An app that draws through its own VirtualDisplay
-     * that has since died, and draws black until it's told about a live one. Taking the surface
+     * (Organic Maps does) can be left pointing at a surface that has since died, and draws black
-     * back and lending it again repoints it; a surface that has itself died is replaced.
+     * until it's told about a live one.
+     *
+     * Always a new surface, never the same one lent again: such an app (Flitsmeister does) builds
+     * its new display on the re-lent surface before releasing the old, and the old one's
+     * disconnect then takes the shared BufferQueue's connection with it - the map freezes on its
+     * last frame for good. The stage's key on [surfaceEpoch] swaps in a new SurfaceView, which
+     * lends itself as it comes up.
      */
-    fun refreshSurface() {
+    fun renewSurface() {
         main.post {
             val current = lent ?: return@post
-            if (!current.surface.isValid) {
+            GearslipLog.i("host: building a fresh surface as the map goes out of view")
-                GearslipLog.w("host: the lent surface died; building a new one")
+            replaceSurface(current)
-                lent = null
-                sendSurfaceDestroyed(current)
-                _surfaceEpoch.value = _surfaceEpoch.value + 1
-                return@post
-            }
-            GearslipLog.i("host: lending the surface again as the map comes back")
-            sendSurfaceDestroyed(current)
-            sendSurfaceAvailable()
         }
     }
 
+    /**
+     * Called as the map comes back into view: replaces the surface only if it died while the map
+     * was covered, since a new one shows black until the app's next frame.
+     */
+    fun replaceDeadSurface() {
+        main.post {
+            val current = lent ?: return@post
+            if (current.surface.isValid) return@post
+            GearslipLog.w("host: the lent surface died; building a new one")
+            replaceSurface(current)
+        }
+    }
+
+    private fun replaceSurface(current: Lent) {
+        lent = null
+        sendSurfaceDestroyed(current)
+        _surfaceEpoch.value = _surfaceEpoch.value + 1
+    }
+
     private fun sendSurfaceAvailable() {
         val callback = surfaceCallback ?: return
         val surface = lent ?: return