Workaround for blank camera preview when switching to tabletop mode

 Switching to/from tabletop mode causes the underlying SurfaceView to
 destroy and recreate its Surface, but the Camera doesn't know its
 been destroyed. This is a known issue with SurfaceView in Compose.
 See: https://issuetracker.google.com/275157240

 To workaround this issue, detect when the folding state enters or
 leaves tabletop mode and manually invalidate the CameraX
 SurfaceRequest so it will generate a new one.

Author: temcguir

feature/camera/src/main/java/com/android/developers/androidify/camera/CameraScreen.kt

@@ -47,6 +47,7 @@ import androidx.compose.runtime.mutableFloatStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
+import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.geometry.Offset
@@ -70,6 +71,7 @@ import com.google.accompanist.permissions.ExperimentalPermissionsApi
 import com.google.accompanist.permissions.isGranted
 import com.google.accompanist.permissions.rememberPermissionState
 import com.google.accompanist.permissions.shouldShowRationale
+import kotlinx.coroutines.flow.takeWhile
 import kotlinx.coroutines.launch
 
 @OptIn(
@@ -129,6 +131,21 @@ fun CameraPreviewScreen(
                 }
 
                 uiState.surfaceRequest?.let { surface ->
+                    // Workaround for https://issuetracker.google.com/275157240
+                    // When switching to/from tabletop posture, the underlying SurfaceView
+                    // destroys its Surface. Invalidate the SurfaceRequest when this happens
+                    // so CameraX can retrieve the new Surface.
+                    LaunchedEffect(surface) {
+                        val oldIsTableTop = isTableTopPosture(foldingFeature)
+                        snapshotFlow { foldingFeature }
+                            .takeWhile {
+                                val newIsTableTop = isTableTopPosture(it)
+                                val shouldInvalidate = oldIsTableTop != newIsTableTop
+                                if (shouldInvalidate) surface.invalidate()
+                                !shouldInvalidate
+                            }.collect {}
+                    }
+
                     CameraPreviewContent(
                         surfaceRequest = surface,
                         autofocusUiState = uiState.autofocusUiState,