[camera] Add Android & iOS implementations for pausing the camera preview

packages/camera/camera/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.1
+
+* Added functions to pause and resume the camera preview
+
 ## 0.9.0
 
 * Complete rewrite of Android plugin to fix many capture, focus, flash, orientation and exposure issues.

packages/camera/camera/android/src/main/java/io/flutter/plugins/camera/Camera.java

@@ -125,6 +125,8 @@ class Camera
   private MediaRecorder mediaRecorder;
   /** True when recording video. */
   private boolean recordingVideo;
+  /** True when the preview is paused. */
+  private boolean pausedPreview;
 
   private File captureFile;
 
@@ -424,8 +426,10 @@ private void refreshPreviewCaptureSession(
     }
 
     try {
-      captureSession.setRepeatingRequest(
-          previewRequestBuilder.build(), cameraCaptureCallback, backgroundHandler);
+      if (!pausedPreview) {
+        captureSession.setRepeatingRequest(
+            previewRequestBuilder.build(), cameraCaptureCallback, backgroundHandler);
+      }
 
       if (onSuccessCallback != null) {
         onSuccessCallback.run();
@@ -830,33 +834,36 @@ public void setFocusMode(final Result result, @NonNull FocusMode newMode) {
      * For focus mode an extra step of actually locking/unlocking the
      * focus has to be done, in order to ensure it goes into the correct state.
      */
-    switch (newMode) {
-      case locked:
-        // Perform a single focus trigger.
-        lockAutoFocus();
-        if (captureSession == null) {
-          Log.i(TAG, "[unlockAutoFocus] captureSession null, returning");
-          return;
-        }
-
-        // Set AF state to idle again.
-        previewRequestBuilder.set(
-            CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_IDLE);
-
-        try {
-          captureSession.setRepeatingRequest(
-              previewRequestBuilder.build(), null, backgroundHandler);
-        } catch (CameraAccessException e) {
-          if (result != null) {
-            result.error("setFocusModeFailed", "Error setting focus mode: " + e.getMessage(), null);
+    if (!pausedPreview) {
+      switch (newMode) {
+        case locked:
+          // Perform a single focus trigger.
+          if (captureSession == null) {
+            Log.i(TAG, "[unlockAutoFocus] captureSession null, returning");
+            return;
+          }
+          lockAutoFocus();
+
+          // Set AF state to idle again.
+          previewRequestBuilder.set(
+              CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_IDLE);
+
+          try {
+            captureSession.setRepeatingRequest(
+                previewRequestBuilder.build(), null, backgroundHandler);
+          } catch (CameraAccessException e) {
+            if (result != null) {
+              result.error(
+                  "setFocusModeFailed", "Error setting focus mode: " + e.getMessage(), null);
+            }
+            return;
           }
-          return;
-        }
-        break;
-      case auto:
-        // Cancel current AF trigger and set AF to idle again.
-        unlockAutoFocus();
-        break;
+          break;
+        case auto:
+          // Cancel current AF trigger and set AF to idle again.
+          unlockAutoFocus();
+          break;
+      }
     }
 
     if (result != null) {
@@ -962,6 +969,19 @@ public void unlockCaptureOrientation() {
     cameraFeatures.getSensorOrientation().unlockCaptureOrientation();
   }
 
+  /** Pause the preview from dart. */
+  public void pausePreview() throws CameraAccessException {
+    this.pausedPreview = true;
+    this.captureSession.stopRepeating();
+  }
+
+  /** Resume the preview from dart. */
+  public void resumePreview() throws CameraAccessException {
+    this.pausedPreview = false;
+    this.refreshPreviewCaptureSession(
+        null, (code, message) -> dartMessenger.sendCameraErrorEvent(message));
+  }
+
   public void startPreview() throws CameraAccessException {
     if (pictureImageReader == null || pictureImageReader.getSurface() == null) return;
     Log.i(TAG, "startPreview");
@@ -1018,8 +1038,8 @@ public void onError(String errorCode, String errorMessage) {
   private void setImageStreamImageAvailableListener(final EventChannel.EventSink imageStreamSink) {
     imageStreamReader.setOnImageAvailableListener(
         reader -> {
-          // Use acquireNextImage since image reader is only for one image.
           Image img = reader.acquireNextImage();
+          // Use acquireNextImage since image reader is only for one image.
           if (img == null) return;
 
           List<Map<String, Object>> planes = new ArrayList<>();

packages/camera/camera/android/src/main/java/io/flutter/plugins/camera/MethodCallHandlerImpl.java

@@ -339,6 +339,26 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull final Result result)
           }
           break;
         }
+      case "pausePreview":
+        {
+          try {
+            camera.pausePreview();
+            result.success(null);
+          } catch (Exception e) {
+            handleException(e, result);
+          }
+          break;
+        }
+      case "resumePreview":
+        {
+          try {
+            camera.resumePreview();
+            result.success(null);
+          } catch (Exception e) {
+            handleException(e, result);
+          }
+          break;
+        }
       case "dispose":
         {
           if (camera != null) {

packages/camera/camera/example/lib/main.dart

@@ -530,7 +530,16 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
                   cameraController.value.isRecordingVideo
               ? onStopButtonPressed
               : null,
-        )
+        ),
+        IconButton(
+          icon: const Icon(Icons.pause_presentation),
+          color:
+              cameraController != null && cameraController.value.isPreviewPaused
+                  ? Colors.red
+                  : Colors.blue,
+          onPressed:
+              cameraController == null ? null : onPausePreviewButtonPressed,
+        ),
       ],
     );
   }
@@ -747,6 +756,23 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
     });
   }
 
+  Future<void> onPausePreviewButtonPressed() async {
+    final CameraController? cameraController = controller;
+
+    if (cameraController == null || !cameraController.value.isInitialized) {
+      showInSnackBar('Error: select a camera first.');
+      return;
+    }
+
+    if (cameraController.value.isPreviewPaused) {
+      await cameraController.resumePreview();
+    } else {
+      await cameraController.pausePreview();
+    }
+
+    if (mounted) setState(() {});
+  }
+
   void onPauseButtonPressed() {
     pauseVideoRecording().then((_) {
       if (mounted) setState(() {});

packages/camera/camera/ios/Classes/CameraPlugin.m

@@ -330,6 +330,7 @@ @interface FLTCam : NSObject <FlutterTexture,
 @property(assign, nonatomic) BOOL audioIsDisconnected;
 @property(assign, nonatomic) BOOL isAudioSetup;
 @property(assign, nonatomic) BOOL isStreamingImages;
+@property(assign, nonatomic) BOOL isPreviewPaused;
 @property(assign, nonatomic) ResolutionPreset resolutionPreset;
 @property(assign, nonatomic) ExposureMode exposureMode;
 @property(assign, nonatomic) FocusMode focusMode;
@@ -1030,6 +1031,16 @@ - (void)applyFocusMode:(FocusMode)focusMode onDevice:(AVCaptureDevice *)captureD
   [captureDevice unlockForConfiguration];
 }
 
+- (void)pausePreviewWithResult:(FlutterResult)result {
+  _isPreviewPaused = true;
+  result(nil);
+}
+
+- (void)resumePreviewWithResult:(FlutterResult)result {
+  _isPreviewPaused = false;
+  result(nil);
+}
+
 - (CGPoint)getCGPointForCoordsWithOrientation:(UIDeviceOrientation)orientation
                                             x:(double)x
                                             y:(double)y {
@@ -1427,7 +1438,9 @@ - (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FlutterResult)re
 
       __weak CameraPlugin *weakSelf = self;
       _camera.onFrameAvailable = ^{
-        [weakSelf.registry textureFrameAvailable:cameraId];
+        if (![weakSelf.camera isPreviewPaused]) {
+          [weakSelf.registry textureFrameAvailable:cameraId];
+        }
       };
       FlutterMethodChannel *methodChannel = [FlutterMethodChannel
           methodChannelWithName:[NSString stringWithFormat:@"flutter.io/cameraPlugin/camera%lu",
@@ -1514,6 +1527,10 @@ - (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FlutterResult)re
         y = ((NSNumber *)call.arguments[@"y"]).doubleValue;
       }
       [_camera setFocusPointWithResult:result x:x y:y];
+    } else if ([@"pausePreview" isEqualToString:call.method]) {
+      [_camera pausePreviewWithResult:result];
+    } else if ([@"resumePreview" isEqualToString:call.method]) {
+      [_camera resumePreviewWithResult:result];
     } else {
       result(FlutterMethodNotImplemented);
     }

packages/camera/camera/lib/src/camera_controller.dart

@@ -47,6 +47,8 @@ class CameraValue {
     required this.deviceOrientation,
     this.lockedCaptureOrientation,
     this.recordingOrientation,
+    this.isPreviewPaused = false,
+    this.previewPauseOrientation,
   }) : _isRecordingPaused = isRecordingPaused;
 
   /// Creates a new camera controller state for an uninitialized controller.
@@ -63,6 +65,7 @@ class CameraValue {
           focusMode: FocusMode.auto,
           focusPointSupported: false,
           deviceOrientation: DeviceOrientation.portraitUp,
+          isPreviewPaused: false,
         );
 
   /// True after [CameraController.initialize] has completed successfully.
@@ -79,6 +82,12 @@ class CameraValue {
 
   final bool _isRecordingPaused;
 
+  /// True when the preview widget has been paused manually.
+  final bool isPreviewPaused;
+
+  /// Set to the orientation the preview was paused in, if it is currently paused.
+  final DeviceOrientation? previewPauseOrientation;
+
   /// True when camera [isRecordingVideo] and recording is paused.
   bool get isRecordingPaused => isRecordingVideo && _isRecordingPaused;
 
@@ -150,6 +159,8 @@ class CameraValue {
     DeviceOrientation? deviceOrientation,
     Optional<DeviceOrientation>? lockedCaptureOrientation,
     Optional<DeviceOrientation>? recordingOrientation,
+    bool? isPreviewPaused,
+    Optional<DeviceOrientation>? previewPauseOrientation,
   }) {
     return CameraValue(
       isInitialized: isInitialized ?? this.isInitialized,
@@ -172,6 +183,10 @@ class CameraValue {
       recordingOrientation: recordingOrientation == null
           ? this.recordingOrientation
           : recordingOrientation.orNull,
+      isPreviewPaused: isPreviewPaused ?? this.isPreviewPaused,
+      previewPauseOrientation: previewPauseOrientation == null
+          ? this.previewPauseOrientation
+          : previewPauseOrientation.orNull,
     );
   }
 
@@ -190,7 +205,9 @@ class CameraValue {
         'focusPointSupported: $focusPointSupported, '
         'deviceOrientation: $deviceOrientation, '
         'lockedCaptureOrientation: $lockedCaptureOrientation, '
-        'recordingOrientation: $recordingOrientation)';
+        'recordingOrientation: $recordingOrientation, '
+        'isPreviewPaused: $isPreviewPaused, '
+        'previewPausedOrientation: $previewPauseOrientation)';
   }
 }
 
@@ -325,6 +342,35 @@ class CameraController extends ValueNotifier<CameraValue> {
     await CameraPlatform.instance.prepareForVideoRecording();
   }
 
+  /// Pauses the current camera preview
+  Future<void> pausePreview() async {
+    if (value.isPreviewPaused) {
+      return;
+    }
+    try {
+      await CameraPlatform.instance.pausePreview(_cameraId);
+      value = value.copyWith(
+          isPreviewPaused: true,
+          previewPauseOrientation: Optional.of(this.value.deviceOrientation));
+    } on PlatformException catch (e) {
+      throw CameraException(e.code, e.message);
+    }
+  }
+
+  /// Resumes the current camera preview
+  Future<void> resumePreview() async {
+    if (!value.isPreviewPaused) {
+      return;
+    }
+    try {
+      await CameraPlatform.instance.resumePreview(_cameraId);
+      value = value.copyWith(
+          isPreviewPaused: false, previewPauseOrientation: Optional.absent());
+    } on PlatformException catch (e) {
+      throw CameraException(e.code, e.message);
+    }
+  }
+
   /// Captures an image and returns the file where it was saved.
   ///
   /// Throws a [CameraException] if the capture fails.

packages/camera/camera/lib/src/camera_preview.dart

@@ -71,7 +71,8 @@ class CameraPreview extends StatelessWidget {
   DeviceOrientation _getApplicableOrientation() {
     return controller.value.isRecordingVideo
         ? controller.value.recordingOrientation!
-        : (controller.value.lockedCaptureOrientation ??
+        : (controller.value.previewPauseOrientation ??
+            controller.value.lockedCaptureOrientation ??
             controller.value.deviceOrientation);
   }
 }

packages/camera/camera/pubspec.yaml

@@ -4,7 +4,7 @@ description: A Flutter plugin for getting information about and controlling the
   and streaming image buffers to dart.
 repository: https://github.com/flutter/plugins/tree/master/packages/camera/camera
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.9.0
+version: 0.9.1
 
 environment:
   sdk: ">=2.12.0 <3.0.0"
@@ -20,7 +20,7 @@ flutter:
         pluginClass: CameraPlugin
 
 dependencies:
-  camera_platform_interface: ^2.0.0
+  camera_platform_interface: ^2.1.0
   flutter:
     sdk: flutter
   pedantic: ^1.10.0

packages/camera/camera/test/camera_preview_test.dart

@@ -113,6 +113,12 @@ class FakeController extends ValueNotifier<CameraValue>
 
   @override
   Future<void> unlockCaptureOrientation() async {}
+
+  @override
+  Future<void> pausePreview() async {}
+
+  @override
+  Future<void> resumePreview() async {}
 }
 
 void main() {