[camera_web] Do not flip the video on the back camera (flutter#4281)

* feat: do not flip the video on the back camera

* test: do not flip the video on the back camera tests

* feat: update getVideoSize usage

packages/camera/camera_web/example/integration_test/camera_test.dart

@@ -85,11 +85,17 @@ void main() {
           'creates a video element '
           'with correct properties', (tester) async {
         const audioConstraints = AudioConstraints(enabled: true);
+        final videoConstraints = VideoConstraints(
+          facingMode: FacingModeConstraint(
+            CameraType.user,
+          ),
+        );
 
         final camera = Camera(
           textureId: textureId,
           options: CameraOptions(
             audio: audioConstraints,
+            video: videoConstraints,
           ),
           cameraService: cameraService,
         );
@@ -108,6 +114,27 @@ void main() {
         expect(camera.videoElement.style.width, equals('100%'));
         expect(camera.videoElement.style.height, equals('100%'));
         expect(camera.videoElement.style.objectFit, equals('cover'));
+      });
+
+      testWidgets(
+          'flips the video element horizontally '
+          'for a back camera', (tester) async {
+        final videoConstraints = VideoConstraints(
+          facingMode: FacingModeConstraint(
+            CameraType.environment,
+          ),
+        );
+
+        final camera = Camera(
+          textureId: textureId,
+          options: CameraOptions(
+            video: videoConstraints,
+          ),
+          cameraService: cameraService,
+        );
+
+        await camera.initialize();
+
         expect(camera.videoElement.style.transform, equals('scaleX(-1)'));
       });
 
@@ -376,7 +403,7 @@ void main() {
         await camera.initialize();
 
         expect(
-          await camera.getVideoSize(),
+          camera.getVideoSize(),
           equals(videoSize),
         );
       });
@@ -396,7 +423,7 @@ void main() {
         await camera.initialize();
 
         expect(
-          await camera.getVideoSize(),
+          camera.getVideoSize(),
           equals(Size.zero),
         );
       });
@@ -819,6 +846,87 @@ void main() {
       });
     });
 
+    group('getLensDirection', () {
+      testWidgets(
+          'returns a lens direction '
+          'based on the first video track settings', (tester) async {
+        final videoElement = MockVideoElement();
+
+        final camera = Camera(
+          textureId: textureId,
+          cameraService: cameraService,
+        )..videoElement = videoElement;
+
+        final firstVideoTrack = MockMediaStreamTrack();
+
+        when(() => videoElement.srcObject).thenReturn(
+          FakeMediaStream([
+            firstVideoTrack,
+            MockMediaStreamTrack(),
+          ]),
+        );
+
+        when(firstVideoTrack.getSettings)
+            .thenReturn({'facingMode': 'environment'});
+
+        when(() => cameraService.mapFacingModeToLensDirection('environment'))
+            .thenReturn(CameraLensDirection.external);
+
+        expect(
+          camera.getLensDirection(),
+          equals(CameraLensDirection.external),
+        );
+      });
+
+      testWidgets(
+          'returns null '
+          'if the first video track is missing the facing mode',
+          (tester) async {
+        final videoElement = MockVideoElement();
+
+        final camera = Camera(
+          textureId: textureId,
+          cameraService: cameraService,
+        )..videoElement = videoElement;
+
+        final firstVideoTrack = MockMediaStreamTrack();
+
+        when(() => videoElement.srcObject).thenReturn(
+          FakeMediaStream([
+            firstVideoTrack,
+            MockMediaStreamTrack(),
+          ]),
+        );
+
+        when(firstVideoTrack.getSettings).thenReturn({});
+
+        expect(
+          camera.getLensDirection(),
+          isNull,
+        );
+      });
+
+      testWidgets(
+          'returns null '
+          'if the camera is missing video tracks', (tester) async {
+        // Create a video stream with no video tracks.
+        final videoElement = VideoElement();
+        mediaStream = videoElement.captureStream();
+
+        final camera = Camera(
+          textureId: textureId,
+          cameraService: cameraService,
+        );
+
+        await camera.initialize();
+
+        expect(
+          camera.getLensDirection(),
+          isNull,
+        );
+      });
+    });
+
     group('getViewType', () {
       testWidgets('returns a correct view type', (tester) async {
         final camera = Camera(

packages/camera/camera_web/example/integration_test/camera_web_test.dart

@@ -574,9 +574,7 @@ void main() {
         abortStreamController = StreamController<Event>();
         endedStreamController = StreamController<MediaStreamTrack>();
 
-        when(camera.getVideoSize).thenAnswer(
-          (_) => Future.value(Size(10, 10)),
-        );
+        when(camera.getVideoSize).thenReturn(Size(10, 10));
         when(camera.initialize).thenAnswer((_) => Future.value());
         when(camera.play).thenAnswer((_) => Future.value());
 
@@ -1660,9 +1658,7 @@ void main() {
         abortStreamController = StreamController<Event>();
         endedStreamController = StreamController<MediaStreamTrack>();
 
-        when(camera.getVideoSize).thenAnswer(
-          (_) => Future.value(Size(10, 10)),
-        );
+        when(camera.getVideoSize).thenReturn(Size(10, 10));
         when(camera.initialize).thenAnswer((_) => Future.value());
         when(camera.play).thenAnswer((_) => Future.value());
         when(camera.dispose).thenAnswer((_) => Future.value());
@@ -1818,9 +1814,7 @@ void main() {
         abortStreamController = StreamController<Event>();
         endedStreamController = StreamController<MediaStreamTrack>();
 
-        when(camera.getVideoSize).thenAnswer(
-          (_) => Future.value(Size(10, 10)),
-        );
+        when(camera.getVideoSize).thenReturn(Size(10, 10));
         when(camera.initialize).thenAnswer((_) => Future.value());
         when(camera.play).thenAnswer((_) => Future.value());
 

packages/camera/camera_web/lib/src/camera.dart

@@ -106,7 +106,6 @@ class Camera {
     );
 
     videoElement = html.VideoElement();
-    _applyDefaultVideoStyles(videoElement);
 
     divElement = html.DivElement()
       ..style.setProperty('object-fit', 'cover')
@@ -123,6 +122,8 @@ class Camera {
       ..srcObject = stream
       ..setAttribute('playsinline', '');
 
+    _applyDefaultVideoStyles(videoElement);
+
     final videoTracks = stream!.getVideoTracks();
 
     if (videoTracks.isNotEmpty) {
@@ -149,7 +150,7 @@ class Camera {
   }
 
   /// Pauses the camera stream on the current frame.
-  void pause() async {
+  void pause() {
     videoElement.pause();
   }
 
@@ -185,11 +186,17 @@ class Camera {
     final videoWidth = videoElement.videoWidth;
     final videoHeight = videoElement.videoHeight;
     final canvas = html.CanvasElement(width: videoWidth, height: videoHeight);
+    final isBackCamera = getLensDirection() == CameraLensDirection.back;
+
+    // Flip the picture horizontally if it is not taken from a back camera.
+    if (!isBackCamera) {
+      canvas.context2D
+        ..translate(videoWidth, 0)
+        ..scale(-1, 1);
+    }
 
     canvas.context2D
-      ..translate(videoWidth, 0)
-      ..scale(-1, 1)
-      ..drawImageScaled(videoElement, 0, 0, videoWidth, videoHeight);
+        .drawImageScaled(videoElement, 0, 0, videoWidth, videoHeight);
 
     final blob = await canvas.toBlob('image/jpeg');
 
@@ -204,7 +211,7 @@ class Camera {
   ///
   /// Returns [Size.zero] if the camera is missing a video track or
   /// the video track does not include the width or height setting.
-  Future<Size> getVideoSize() async {
+  Size getVideoSize() {
     final videoTracks = videoElement.srcObject?.getVideoTracks() ?? [];
 
     if (videoTracks.isEmpty) {
@@ -332,6 +339,29 @@ class Camera {
     });
   }
 
+  /// Returns a lens direction of this camera.
+  ///
+  /// Returns null if the camera is missing a video track or
+  /// the video track does not include the facing mode setting.
+  CameraLensDirection? getLensDirection() {
+    final videoTracks = videoElement.srcObject?.getVideoTracks() ?? [];
+
+    if (videoTracks.isEmpty) {
+      return null;
+    }
+
+    final defaultVideoTrack = videoTracks.first;
+    final defaultVideoTrackSettings = defaultVideoTrack.getSettings();
+
+    final facingMode = defaultVideoTrackSettings['facingMode'];
+
+    if (facingMode != null) {
+      return _cameraService.mapFacingModeToLensDirection(facingMode);
+    } else {
+      return null;
+    }
+  }
+
   /// Returns the registered view type of the camera.
   String getViewType() => _getViewType(textureId);
 
@@ -354,12 +384,18 @@ class Camera {
 
   /// Applies default styles to the video [element].
   void _applyDefaultVideoStyles(html.VideoElement element) {
+    final isBackCamera = getLensDirection() == CameraLensDirection.back;
+
+    // Flip the video horizontally if it is not taken from a back camera.
+    if (!isBackCamera) {
+      element.style.transform = 'scaleX(-1)';
+    }
+
     element.style
       ..transformOrigin = 'center'
       ..pointerEvents = 'none'
       ..width = '100%'
       ..height = '100%'
-      ..objectFit = 'cover'
-      ..transform = 'scaleX(-1)';
+      ..objectFit = 'cover';
   }
 }

packages/camera/camera_web/lib/src/camera_web.dart

@@ -285,7 +285,7 @@ class CameraPlugin extends CameraPlatform {
         );
       });
 
-      final cameraSize = await camera.getVideoSize();
+      final cameraSize = camera.getVideoSize();
 
       cameraEventStreamController.add(
         CameraInitializedEvent(