Resync the zoom bar with the lens on every camera rebind.

feature/camera/src/main/java/org/signal/camera/CameraScreenViewModel.kt

@@ -94,8 +94,11 @@ class CameraScreenViewModel : ViewModel() {
     /** Requested resolution for the QR analysis stream. */
     private val QR_ANALYSIS_RESOLUTION = Size(1280, 720)
 
+    /** Where a lens comes up after a bind, and so where the zoom goes back to on every bind. */
+    private const val DEFAULT_ZOOM_RATIO = 1f
+
     /** A single point, so a lens that has not reported its range yet reads as one that cannot zoom. */
-    private val DEFAULT_ZOOM_RANGE = 1f..1f
+    private val DEFAULT_ZOOM_RANGE = DEFAULT_ZOOM_RATIO..DEFAULT_ZOOM_RATIO
 
     /** How long a zoom animation to a level picked off the zoom bar runs for. */
     private const val ZOOM_ANIMATION_DURATION_MS = 250L
@@ -123,7 +126,7 @@ class CameraScreenViewModel : ViewModel() {
   private var brightnessWindow: WeakReference<Window>? = null
   private var deviceTargetRotation: Int = Surface.ROTATION_0
   private var surfaceProvider: Preview.SurfaceProvider? = null
-  private var recordingStartZoomRatio: Float = 1f
+  private var recordingStartZoomRatio: Float = DEFAULT_ZOOM_RATIO
 
   /** The in-flight animation to a level picked off the zoom bar. Anything else that moves the zoom cancels it. */
   private var zoomAnimation: Job? = null
@@ -135,12 +138,6 @@ class CameraScreenViewModel : ViewModel() {
    */
   private var pendingRecordingLock: Boolean = false
 
-  /**
-   * Set when a lens is bound, so that the first zoom it reports is taken as the current ratio. A rebind comes up at the
-   * new lens's own zoom rather than carrying the previous one's over.
-   */
-  private var needsZoomResync: Boolean = false
-
   /** Null for a recording that finalizes without being asked to stop, such as one that hits the recorder's own limits. */
   private var recordingStopwatch: Stopwatch? = null
 
@@ -168,12 +165,7 @@ class CameraScreenViewModel : ViewModel() {
   private val zoomRangeObserver = Observer<ZoomState> { zoomState ->
     val zoomRange = zoomState.minZoomRatio..zoomState.maxZoomRatio
 
-    if (needsZoomResync) {
-      needsZoomResync = false
-      Log.d(TAG, "Bound lens reaches $zoomRange at ${zoomState.zoomRatio}x")
-      recordingStartZoomRatio = zoomState.zoomRatio
-      _state.value = _state.value.copy(zoomRange = zoomRange, zoomRatio = zoomState.zoomRatio)
-    } else if (zoomRange != _state.value.zoomRange) {
+    if (zoomRange != _state.value.zoomRange) {
       Log.d(TAG, "Bound lens reaches $zoomRange")
       _state.value = _state.value.copy(zoomRange = zoomRange)
     }
@@ -909,20 +901,25 @@ class CameraScreenViewModel : ViewModel() {
   }
 
   /**
-   * Observes what the bound lens can reach. A camera reports its zoom when it is ready rather than by the time it is
-   * bound, so this observes rather than taking a single reading — a lens whose range arrives late would otherwise look
-   * like one that cannot zoom.
+   * Puts the zoom back to [DEFAULT_ZOOM_RATIO] and observes what the bound lens can reach. A camera reports its range
+   * when it is ready rather than by the time it is bound, so this observes rather than taking a single reading — a lens
+   * whose range arrives late would otherwise look like one that cannot zoom.
    */
   private fun observeZoomRange() {
     val zoomState = camera?.cameraInfo?.zoomState
 
+    // Every bind here follows an unbind, which drops the lens back to its default zoom. The state follows it back down,
+    // and an in-flight travel to a level picked before the unbind is left with nowhere to land.
+    zoomAnimation?.cancel()
+    recordingStartZoomRatio = DEFAULT_ZOOM_RATIO
+    _state.value = _state.value.copy(zoomRatio = DEFAULT_ZOOM_RATIO)
+
     if (zoomState === observedZoomState) {
       return
     }
 
     observedZoomState?.removeObserver(zoomRangeObserver)
     observedZoomState = zoomState
-    needsZoomResync = true
 
     if (zoomState != null) {
       zoomState.observeForever(zoomRangeObserver)

feature/camera/src/test/java/org/signal/camera/CameraScreenViewModelTest.kt

@@ -748,17 +748,38 @@ class CameraScreenViewModelTest {
     assertThat(viewModel.state.value.zoomRange).isEqualTo(1f..3f)
   }
 
-  /** A newly bound lens comes up at its own zoom rather than carrying over whatever the one before it was at. */
+  /**
+   * Coming back into the camera rebinds it, which drops the lens back to its default zoom, so the zoom bar goes back
+   * with it rather than keeping a level highlighted over a preview that is no longer at it.
+   */
   @Test
-  fun `Given a lens sitting away from 1x, when bound, then its own zoom is published`() {
-    setupZoomState(minZoom = 1f, maxZoom = 10f, zoomRatio = 5f)
+  fun `Given a lens that has been zoomed, when rebound, then the zoom is back at 1x`() {
+    setupZoomState(minZoom = 1f, maxZoom = 8f)
+    bindCamera()
+    viewModel.onEvent(CameraScreenEvents.SetZoomRatio(5f))
+    testDispatcher.scheduler.advanceUntilIdle()
+    assertThat(viewModel.state.value.zoomRatio).isEqualTo(5f)
 
     bindCamera()
 
-    assertThat(viewModel.state.value.zoomRatio).isEqualTo(5f)
+    assertThat(viewModel.state.value.zoomRatio).isEqualTo(1f)
   }
 
-  /** The resync happens once per binding, so it cannot pull the lens back from wherever it has since been sent. */
+  /** The reset happens on the bind itself, so a lens reporting afterwards cannot pull it back off 1x. */
+  @Test
+  fun `Given a rebound lens, when it reports the zoom it was left at, then the zoom stays at 1x`() {
+    setupZoomState(minZoom = 1f, maxZoom = 8f)
+    bindCamera()
+    viewModel.onEvent(CameraScreenEvents.SetZoomRatio(5f))
+    testDispatcher.scheduler.advanceUntilIdle()
+
+    bindCamera()
+    setupZoomState(minZoom = 1f, maxZoom = 8f, zoomRatio = 5f)
+
+    assertThat(viewModel.state.value.zoomRatio).isEqualTo(1f)
+  }
+
+  /** The reset happens on the bind, so it cannot pull the lens back from wherever it has since been sent. */
   @Test
   fun `Given a bound lens that has been zoomed, when it reports again, then the zoom it was sent to stands`() {
     setupZoomState(minZoom = 1f, maxZoom = 10f, zoomRatio = 1f)