[camera_web] Support getting cameras while a camera is being used.

Author: kristoffer-zliide

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

@@ -64,7 +64,7 @@ void main() {
       when(
         () => cameraService.getMediaStreamForOptions(
           any(),
-          cameraId: any(named: 'cameraId'),
+          cameraId: any(),
         ),
       ).thenAnswer(
         (_) async => videoElement.captureStream(),

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

@@ -43,6 +43,7 @@ class CameraPlugin extends CameraPlatform {
   @visibleForTesting
   final Map<int, Camera> cameras = <int, Camera>{};
   int _textureCounter = 1;
+  List<CameraDescription>? _availableCameras;
 
   /// Metadata associated with each camera description.
   /// Populated in [availableCameras].
@@ -81,48 +82,60 @@ class CameraPlugin extends CameraPlatform {
   @visibleForTesting
   html.Window? window = html.window;
 
-  @override
-  Future<List<CameraDescription>> availableCameras() async {
-    try {
-      final html.MediaDevices? mediaDevices = window?.navigator.mediaDevices;
-      final List<CameraDescription> cameras = <CameraDescription>[];
+  Future<List<html.MediaDeviceInfo>> _videoInputDevices() async {
+    final html.MediaDevices? mediaDevices = window?.navigator.mediaDevices;
 
-      // Throw a not supported exception if the current browser window
-      // does not support any media devices.
-      if (mediaDevices == null) {
-        throw PlatformException(
-          code: CameraErrorCode.notSupported.toString(),
-          message: 'The camera is not supported on this device.',
-        );
-      }
+    // Throw a not supported exception if the current browser window
+    // does not support any media devices.
+    if (mediaDevices == null) {
+      throw PlatformException(
+        code: CameraErrorCode.notSupported.toString(),
+        message: 'The camera is not supported on this device.',
+      );
+    }
 
-      // Request video permissions only.
-      final html.MediaStream cameraStream =
-          await _cameraService.getMediaStreamForOptions(const CameraOptions());
+    // Request available media devices.
+    final List<dynamic> devices = await mediaDevices.enumerateDevices();
 
-      // Release the camera stream used to request video permissions.
-      cameraStream
-          .getVideoTracks()
-          .forEach((html.MediaStreamTrack videoTrack) => videoTrack.stop());
+    // Filter video input devices.
+    final Iterable<html.MediaDeviceInfo> videoInputDevices = devices
+        .whereType<html.MediaDeviceInfo>()
+        .where((html.MediaDeviceInfo device) =>
+            device.kind == MediaDeviceKind.videoInput)
 
-      // Request available media devices.
-      final List<dynamic> devices = await mediaDevices.enumerateDevices();
+        /// The device id property is currently not supported on Internet Explorer:
+        /// https://developer.mozilla.org/en-US/docs/Web/API/MediaDeviceInfo/deviceId#browser_compatibility
+        .where(
+          (html.MediaDeviceInfo device) =>
+              device.deviceId != null && device.deviceId!.isNotEmpty,
+        );
 
-      // Filter video input devices.
-      final Iterable<html.MediaDeviceInfo> videoInputDevices = devices
-          .whereType<html.MediaDeviceInfo>()
-          .where((html.MediaDeviceInfo device) =>
-              device.kind == MediaDeviceKind.videoInput)
+    return videoInputDevices.toList();
+  }
 
-          /// The device id property is currently not supported on Internet Explorer:
-          /// https://developer.mozilla.org/en-US/docs/Web/API/MediaDeviceInfo/deviceId#browser_compatibility
-          .where(
-            (html.MediaDeviceInfo device) =>
-                device.deviceId != null && device.deviceId!.isNotEmpty,
-          );
+  @override
+  Future<List<CameraDescription>> availableCameras() async {
+    if (_availableCameras != null) {
+      return _availableCameras!;
+    }
+    try {
+      final List<CameraDescription> cameraDescriptions = <CameraDescription>[];
+
+      final bool hasPermission = cameras.isNotEmpty;
+      if (!hasPermission) {
+        // Request video permissions only.
+        final html.MediaStream cameraStream = await _cameraService
+            .getMediaStreamForOptions(const CameraOptions());
+
+        // Release the camera stream used to request video permissions.
+        cameraStream
+            .getVideoTracks()
+            .forEach((html.MediaStreamTrack videoTrack) => videoTrack.stop());
+      }
 
       // Map video input devices to camera descriptions.
-      for (final html.MediaDeviceInfo videoInputDevice in videoInputDevices) {
+      for (final html.MediaDeviceInfo videoInputDevice
+          in await _videoInputDevices()) {
         // Get the video stream for the current video input device
         // to later use for the available video tracks.
         final html.MediaStream videoStream = await _getVideoStreamForDevice(
@@ -134,54 +147,57 @@ class CameraPlugin extends CameraPlatform {
         final List<html.MediaStreamTrack> videoTracks =
             videoStream.getVideoTracks();
 
-        if (videoTracks.isNotEmpty) {
-          // Get the facing mode from the first available video track.
-          final String? facingMode =
-              _cameraService.getFacingModeForVideoTrack(videoTracks.first);
-
-          // Get the lens direction based on the facing mode.
-          // Fallback to the external lens direction
-          // if the facing mode is not available.
-          final CameraLensDirection lensDirection = facingMode != null
-              ? mapFacingModeToLensDirection(facingMode)
-              : CameraLensDirection.external;
-
-          // Create a camera description.
-          //
-          // The name is a camera label which might be empty
-          // if no permissions to media devices have been granted.
-          //
-          // MediaDeviceInfo.label:
-          // https://developer.mozilla.org/en-US/docs/Web/API/MediaDeviceInfo/label
-          //
-          // Sensor orientation is currently not supported.
-          final String cameraLabel = videoInputDevice.label ?? '';
-          final CameraDescription camera = CameraDescription(
-            name: cameraLabel,
-            lensDirection: lensDirection,
-            sensorOrientation: 0,
-          );
-
-          final CameraMetadata cameraMetadata = CameraMetadata(
-            deviceId: videoInputDevice.deviceId!,
-            facingMode: facingMode,
-          );
-
-          cameras.add(camera);
-
-          camerasMetadata[camera] = cameraMetadata;
+        if (videoTracks.isEmpty) {
+          // Ignore as no video tracks exist in the current video input device.
+          continue;
+        }
+
+        // Get the facing mode from the first available video track.
+        final String? facingMode =
+            _cameraService.getFacingModeForVideoTrack(videoTracks.first);
+
+        // Get the lens direction based on the facing mode.
+        // Fallback to the external lens direction
+        // if the facing mode is not available.
+        final CameraLensDirection lensDirection = facingMode != null
+            ? mapFacingModeToLensDirection(facingMode)
+            : CameraLensDirection.external;
+
+        // Create a camera description.
+        //
+        // The name is a camera label which might be empty
+        // if no permissions to media devices have been granted.
+        //
+        // MediaDeviceInfo.label:
+        // https://developer.mozilla.org/en-US/docs/Web/API/MediaDeviceInfo/label
+        //
+        // Sensor orientation is currently not supported.
+        final String cameraLabel = videoInputDevice.label ?? '';
+        final CameraDescription camera = CameraDescription(
+          name: cameraLabel,
+          lensDirection: lensDirection,
+          sensorOrientation: 0,
+        );
 
+        final CameraMetadata cameraMetadata = CameraMetadata(
+          deviceId: videoInputDevice.deviceId!,
+          facingMode: facingMode,
+        );
+
+        cameraDescriptions.add(camera);
+
+        camerasMetadata[camera] = cameraMetadata;
+
+        if (!hasPermission) {
           // Release the camera stream of the current video input device.
           for (final html.MediaStreamTrack videoTrack in videoTracks) {
             videoTrack.stop();
           }
-        } else {
-          // Ignore as no video tracks exist in the current video input device.
-          continue;
         }
       }
 
-      return cameras;
+      _availableCameras = cameraDescriptions;
+      return cameraDescriptions;
     } on html.DomException catch (e) {
       throw CameraException(e.name, e.message);
     } on PlatformException catch (e) {