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val cameraDevice = Camera.open(0)

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val cameraManager = activity.getSystemService(Context.CAMERA_SERVICE) as CameraManager
val cameraId = cameraManager.cameraIdList[0]
cameraManager.openCamera(cameraId, object : CameraDevice.StateCallback() {
    override fun onOpened(device: CameraDevice) {
        // Do something with `device`
    }
    override fun onDisconnected(device: CameraDevice) {
        device.close()
    }
    override fun onError(device: CameraDevice, error: Int) {

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val cameraIdList = cameraManager.cameraIdList // may be empty
val characteristics = cameraManager.getCameraCharacteristics(cameraId)
val cameraLensFacing = characteristics.get(CameraCharacteristics.LENS_FACING)
val cameraCapabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)
val cameraCompatible = cameraCapabilities?.contains(
        CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false

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fun getFirstCameraIdFacing(cameraManager: CameraManager,
                           facing: Int = CameraMetadata.LENS_FACING_BACK): String? {
    // Get list of all compatible cameras
    val cameraIds = cameraManager.cameraIdList.filter {
        val characteristics = cameraManager.getCameraCharacteristics(it)
        val capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)
        capabilities?.contains(
                CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
    }

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fun filterCompatibleCameras(cameraIds: Array<String>,
                            cameraManager: CameraManager): List<String> {
    return cameraIds.filter {
        val characteristics = cameraManager.getCameraCharacteristics(it)
        characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)?.contains(
                CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
    }
}

fun filterCameraIdsFacing(cameraIds: List<String>, cameraManager: CameraManager,

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// Retrieve the target surfaces, which could be coming from a number of places:
// 1. SurfaceView, if we want to display the image directly to the user
// 2. ImageReader, if we want to read each frame or perform frame-by-frame analysis
// 3. OpenGL Texture / TextureView, although discouraged for maintainability reasons
// 4. RenderScript.Allocation, if we want to do parallel processing
val surfaceView = findViewById<SurfaceView>(...)
val imageReader = ImageReader.newInstance(...)

// Remember to call this only *after* SurfaceHolder.Callback.surfaceCreated()
val previewSurface = surfaceView.holder.surface

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val session: CameraCaptureSession = ...  // from CameraCaptureSession.StateCallback
val captureRequest = session.device.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW)
captureRequest.addTarget(previewSurface)

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val session: CameraCaptureSession = ...  // from CameraCaptureSession.StateCallback
val captureRequest: CaptureRequest = ...  // from CameraDevice.createCaptureRequest()

// The first null argument corresponds to the capture callback, which we should
// provide if we wanted to retrieve frame metadata or keep track of failed capture
// requests that could indicate dropped frames; the second null argument
// corresponds to the Handler used by the asynchronous callback, which will fall
// back to the current thread's looper if null
session.capture(captureRequest.build(), null, null)

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val session: CameraCaptureSession = ...  // from CameraCaptureSession.StateCallback
val captureRequest: CaptureRequest = ...  // from CameraDevice.createCaptureRequest()

// This will keep sending the capture request as frequently as possible until the
// session is torn down or session.stopRepeating() is called
session.setRepeatingRequest(captureRequest.build(), null, null)

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val session: CameraCaptureSession = ...  // from CameraCaptureSession.StateCallback

// Create the repeating request and dispatch it
val repeatingRequest = session.device.createCaptureRequest(
        CameraDevice.TEMPLATE_PREVIEW)
repeatingRequest.addTarget(previewSurface)
session.setRepeatingRequest(repeatingRequest.build(), null, null)

// Some time later...