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<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">

   <com.otaliastudios.cameraview.CameraView
       android:id="@+id/camera_view"

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override fun onCreate(savedInstanceState: Bundle?) {
	…
	checkAndRequestCameraPermission()
}

private fun checkAndRequestCameraPermission() {
   if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.CAMERA)
           != PackageManager.PERMISSION_GRANTED) {
       ActivityCompat.requestPermissions(this, arrayOf(android.Manifest.permission.CAMERA),
               PERMISION_REQUEST_CODE)

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implementation 'com.google.firebase:firebase-core:16.0.1'
implementation 'com.google.firebase:firebase-ml-vision:16.0.0'
implementation "android.arch.lifecycle:extensions:1.1.1"
implementation 'com.otaliastudios:cameraview:1.5.1'

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override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
   if (requestCode == PERMISION_REQUEST_CODE) {
       if (android.Manifest.permission.CAMERA == permissions[0] &&
               grantResults[0] == PackageManager.PERMISSION_GRANTED) {
           startFaceProcessor()
       }
   }
   super.onRequestPermissionsResult(requestCode, permissions, grantResults)
}

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lifecycle.addObserver(MainActivityLifecycleObserver(camera_view))

//MainActivityLifecycleObserver.class
class MainActivityLifecycleObserver(private val cameraView: CameraView) : LifecycleObserver {

   @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
   fun startCamera() {
       cameraView.start()
   }

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cameraView.addFrameProcessor { frame ->
// Processes frame here

}

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// Initialize the face detection option, and we need all the face landmarks
private val options = FirebaseVisionFaceDetectorOptions.Builder()
       .setLandmarkType(FirebaseVisionFaceDetectorOptions.ALL_LANDMARKS)
       .build()

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// Obtain the FirebaseVisionFaceDetector instance
private val detector = FirebaseVision.getInstance().getVisionFaceDetector(options)

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// Build a image meta data object
val metadata = FirebaseVisionImageMetadata.Builder()
       .setFormat(FirebaseVisionImageMetadata.IMAGE_FORMAT_NV21)
       .setWidth(frame.size.width)
       .setHeight(frame.size.height)
       .setRotation(rotation)
       .build()
// Create vision image object, and it will be consumed by FirebaseVisionFaceDetector
// for face detection
val firebaseVisionImage = FirebaseVisionImage.fromByteArray(frame.data, metadata)

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// Perform face detection
detector.detectInImage(firebaseVisionImage).addOnSuccessListener { faceList ->
   if (faceList.size > 0) {
       // We just need the first face
       val face = faceList[0]

       // Draw the bitmaps on the detected faces

   }
}