camera2 api:请求提交后4-5秒拍摄图片

目标很简单:只需使用 前面 照相机。照片应在照片请求发送时固定。甚至不需要预览,因此 CameraSession 使用来自 ImageReader . 但问题是,在某些设备上,图片 捕获 只有4-5秒。以下是一些日志:

要求拍照的时间是13:47:29.049

在13:47:29.062请求捕获

文件已写入,在13:47:33.313向频道发送文件

13:47:33.339收到照片文件

13:47:39.073要求拍照

13:47:39.074请求捕获

文件已写入,将文件发送到13:47:43.199的频道

13:47:43.215收到照片文件

问题是照片是 捕获 4秒后 自动聚焦 不支持此功能(在小米mi-5上测试)。如何消除之前如此长的延迟 捕捉 或者执行焦点锁定?或者这里可能有另一个解决方法来消除所述问题?

值得一提的是华硕的平板电脑日志:

07:07:03.443要求拍照

捕获请求时间:07:07:03.454

文件已写入,正在07:07:03.907将文件发送到频道

照片文件于07:07:03.944收到

07:07:08.449要求拍照

捕获请求于07:07:08.449

文件已写入,正在07:07:08.635将文件发送到频道

照片文件于07:07:08.651收到

代码如下:

ViewModel:

private fun makePhoto() {
    GlobalScope.launch(Main) {
        Log.i("Photo", "Photo was requested at ${LocalTime.now()}")
        val picture: File = camera.makePhoto()
        Log.i("Photo", "Photo file was received at ${LocalTime.now()}")
        //process the file somehow
    }
}

PhotoCamera:

//the method is called in onStart of an Activity or Fragment instance
override suspend fun open() {
    val surfaces = listOf(outputSurface) //surface of an ImageReader instance, comes into object's constructor
    cameraDevice =
        suspendCoroutine { cameraManager.openCamera(specification.id, SuspendingCameraStateCallback(it), handler) } //callback just resumes the coroutine with CameraDevice when onOpened method was called.
    session = suspendCoroutine { cameraDevice.createCaptureSession(surfaces, SuspendSessionCallback(it), handler) } //same, just resumes the continuation with the session that comes into onConfigured method
}

override suspend fun makePhoto(): File {
    return suspendCoroutine {
        session.apply {
            stopRepeating()
            abortCaptures()
            Log.i("Photo", "Capture was requested on ${LocalTime.now()}")
            capture(createCaptureRequest(outputSurface), captureAwaitFactory.createListener(it), handler)
        }
    }
}

private fun createCaptureRequest(target: Surface): CaptureRequest {
    val requestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE)
    requestBuilder.addTarget(target)
    requestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO)
    requestBuilder.set(CaptureRequest.JPEG_ORIENTATION, orientation.rotation)
    return requestBuilder.build()
}

使用setOnImageAvailableListener附加的ImageReader侦听器的代码:

override fun onImageAvailable(reader: ImageReader) {
    reader.acquireLatestImage().use { image: Image ->
        val byteBuffer = image.planes[0].buffer
        val byteArray = ByteArray(byteBuffer.capacity())
        byteBuffer.get(byteArray)
        val outputFile = createOutputFile()
        FileOutputStream(outputFile).use { stream: FileOutputStream -> stream.write(byteArray) }
        Log.i("Photo", "File was written, sending file to the channel on ${LocalTime.now()}")
        scope.launch {
            fileChannel.send(outputFile)
        }
    }
}

private fun createOutputFile() = //creates a unique file

工厂的 createListener 实施:

override fun createListener(continuation: Continuation<File>): CameraCaptureSession.CaptureCallback {
    return CoroutineCaptureCallback(channel, this, continuation)
}

和 CoroutineCaptureCallback 的代码:

internal class CoroutineCaptureCallback(
    private val channel: ReceiveChannel<File>,
    private val scope: CoroutineScope,
    private val continuation: Continuation<File>
) : CameraCaptureSession.CaptureCallback() {

    override fun onCaptureCompleted(
        session: CameraCaptureSession,
        request: CaptureRequest,
        result: TotalCaptureResult
    ) {
        super.onCaptureCompleted(session, request, result)
        scope.launch {
            continuation.resume(channel.receive())
        }
    }
}