在Android上将实时摄像头与AI危害检测配合使用

TextureView不会自动显示的视频提要。相反，我们必须编写代码以使用来自摄像机的图像对其进行更新。当TextureView更新时，我们可以检索Bitmap为正在显示的帧，并传递到Detector。当TextureView准备好显示的内容，它通知SurfaceTextureListener。我们进行SurfaceTextureListener选择，然后打开相机。SurfaceTextureListener的界面如下所示。

SurfaceTextureListener {
   fun onSurfaceTextureAvailable(
       surface: SurfaceTexture, width: Int, height: Int
   )

   fun onSurfaceTextureSizeChanged(
       surface: SurfaceTexture, width: Int, height: Int
   )

   override fun onSurfaceTextureDestroyed(surface: SurfaceTexture): Boolean

   override fun onSurfaceTextureUpdated(surface: SurfaceTexture)
}

函数onSurfaceTextureAvailable和onSurfaceTextureUpdated是最受关注的函数。我们打开相机onSurfaceTextureAvailable并在onSurfaceTextureUpdated中接收更新。

override fun onSurfaceTextureAvailable(
   surface: SurfaceTexture,
   width: Int,
   height: Int
) {
   val cm = getSystemService(CAMERA_SERVICE) as CameraManager
   for (cameraID in cm.cameraIdList) {
      val characteristics = cm.getCameraCharacteristics(cameraID!!)
      if (characteristics.get(CameraCharacteristics.LENS_FACING) == CameraCharacteristics.LENS_FACING_FRONT) {
          continue //Skip front facing camera
      }
      mCameraID = cameraID
      openCamera()
      return
   }
}

在openCamera函数中，我们使用CameraManager打开选定的硬件摄像机。用户界面布局中TextView的SurfaceTexture对象被分配了大小。我们还将为预览构建配置，为预览设置宽度、高度和方向。

val manager = getSystemService(CAMERA_SERVICE) as CameraManager
manager.openCamera(mCameraID!!, mCameraStateCallback!!, mBackgroundHandler)
val texture = camera_preview!!.surfaceTexture
texture!!.setDefaultBufferSize(previewSize!!.width, previewSize!!.height)
val previewSurface = Surface(texture)
mPreviewCaptureRequestBuilder =
   mCameraDevice!!.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW)
mPreviewCaptureRequestBuilder!!.set(CaptureRequest.JPEG_ORIENTATION, mCameraOrientation)
mPreviewCaptureRequestBuilder!!.addTarget(previewSurface)

mCameraDevice!!.createCaptureSession(
   Arrays.asList(previewSurface),
   object : CameraCaptureSession.StateCallback() {
       override fun onConfigured(session: CameraCaptureSession) {
           if (mCameraDevice == null) return
           mPreviewCaptureRequest = mPreviewCaptureRequestBuilder!!.build()
           mCameraCaptureSession = session
           mCameraCaptureSession!!.setRepeatingRequest(
                mPreviewCaptureRequest!!,
                mSessionCaptureCallback,
                mBackgroundHandler
           )
       }
   }, null
)

更新的帧将传递回先前声明的SurfaceTextureListener。在它的onSurfceTextureUpdated方法中，仅需几行代码，就可以获取帧的Bitmap。这个BitMap可以被传递给检测器来寻找危险。

覆盖fun onSurfaceTextureUpdated（surface：SurfaceTexture）{

override fun onSurfaceTextureUpdated(surface: SurfaceTexture) {
   val bitmap = Bitmap.createBitmap(
       camera_preview!!.width,
       camera_preview!!.height,
       Bitmap.Config.ARGB_8888
   )
   camera_preview!!.getBitmap(bitmap)
}

fun requestLocation() {
   locationListener = LocationListener { location ->
       detector.currentSpeedMPS = location.speed
   }

   val locationManager = this.getSystemService(LOCATION_SERVICE) as LocationManager
   val provider = locationManager.getProvider(LocationManager.GPS_PROVIDER)
   val criteria = Criteria()
   criteria.accuracy = Criteria.ACCURACY_FINE
   val providerName = locationManager.getBestProvider(criteria, true)
   val isProviderEnabled = locationManager.isProviderEnabled(providerName!!)
   if (isProviderEnabled) locationManager.requestLocationUpdates(
       providerName,
       1000,
       1f,
       locationListener!!
   )
}