Image streaming WIP #8
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…tform (flutter#7951)" This reverts commit b3a5e33.
When image stream frames are being received from Media Foundation,
it appears to use a separate thread when calling the `OnSample`
callback, which results in this error from:
The 'plugins.flutter.io/camera_windows/imageStream' channel sent a
message from native to Flutter on a non-platform thread. Platform
channel messages must be sent on the platform thread. Failure to do
so may result in data loss or crashes, and must be fixed in the
plugin or application code creating that channel.
In order to ensure that we are only ever using the `EventChannel` from
a platform thread, create a `TaskRunner` that is backed by a hidden
window to submit the frames to the image stream.
Based on the suggestion in this comment:
flutter/flutter#134346 (comment)
Instead of a global `EventSink` that is re-used for each stream, create a dedicated `EventChannel` for each capture stream. The channel gets an unique name like `plugins.flutter.io/camera_android/imageStream/<cameraId>` for each camera instance.
jokerttu
requested changes
Dec 3, 2024
We don’t really need to keep track of the subscription and controller in instance variables. It’ll work fine with a simple `async*` method, cancellation and all.
We need to have exception-throwing `onPause` and `onResume` callback, as they are required to throw by the camera platform interface.
jokerttu
reviewed
Dec 5, 2024
| final eventChannelName = await _hostApi.startImageStream(cameraId); | ||
| final EventChannel imageStreamChannel = | ||
| EventChannel(eventChannelName); | ||
| imageStreamChannel.receiveBroadcastStream().listen((dynamic image) => |
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This creates subscription.
should it be cancelled in onCancel as well.
having
late StreamSubscription subscription;
save the subscription:
subscription = imageStreamChannel.receiveBroadcastStream().listen ...
cancel the subscription:
onCancel: () async {
await subscription.cancel();
await _hostApi.stopImageStream(cameraId);
},
?
Not sure if this is needed though.
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