Jetpack系列(三、行为)

一、CameraX

是一个JetPack支持库，简化相机开发工作，提供易用的API;适配大多数Android设备，兼容低版本至Android5.0
借助CameraX,只需要两行代码就能利用和预安装相机应用相同的相机体验和功能；
还提供了CameraX Extensions可选插件，丰富设备添加的效果，包括人像、HDR、夜间模式、美颜等效果；

主要优势：

• 易用性：
• 设备的一致性：
• 新的相机体验：丰富的插件；

示例：核心代码

1.1预览模式

private fun startCamera() {
   val cameraProviderFuture = ProcessCameraProvider.getInstance(this)

   cameraProviderFuture.addListener(Runnable {
       // Used to bind the lifecycle of cameras to the lifecycle owner
       val cameraProvider: ProcessCameraProvider = cameraProviderFuture.get()

       // Preview
       preview = Preview.Builder()
           .build()

       // Select back camera
       val cameraSelector = CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK).build()

       try {
           // Unbind use cases before rebinding
           cameraProvider.unbindAll()

           // Bind use cases to camera
           camera = cameraProvider.bindToLifecycle(
               this, cameraSelector, preview)
           preview?.setSurfaceProvider(viewFinder.createSurfaceProvider(camera?.cameraInfo))
       } catch(exc: Exception) {
           Log.e(TAG, "Use case binding failed", exc)
       }

   }, ContextCompat.getMainExecutor(this))
}

1.2拍照

private fun takePhoto() {
   // Get a stable reference of the modifiable image capture use case
   val imageCapture = imageCapture ?: return

   // Create timestamped output file to hold the image
   val photoFile = File(
       outputDirectory,
       SimpleDateFormat(FILENAME_FORMAT, Locale.US
       ).format(System.currentTimeMillis()) + ".jpg")

   // Create output options object which contains file + metadata
   val outputOptions = ImageCapture.OutputFileOptions.Builder(photoFile).build()

   // Setup image capture listener which is triggered after photo has
   // been taken
   imageCapture.takePicture(
       outputOptions, ContextCompat.getMainExecutor(this), object : ImageCapture.OnImageSavedCallback {
           override fun onError(exc: ImageCaptureException) {
               Log.e(TAG, "Photo capture failed: ${exc.message}", exc)
           }

           override fun onImageSaved(output: ImageCapture.OutputFileResults) {
               val savedUri = Uri.fromFile(photoFile)
               val msg = "Photo capture succeeded: $savedUri"
               Toast.makeText(baseContext, msg, Toast.LENGTH_SHORT).show()
               Log.d(TAG, msg)
           }
       })
}

1.3图形分析

private class LuminosityAnalyzer(private val listener: LumaListener) : ImageAnalysis.Analyzer {

   private fun ByteBuffer.toByteArray(): ByteArray {
       rewind()    // Rewind the buffer to zero
       val data = ByteArray(remaining())
       get(data)   // Copy the buffer into a byte array
       return data // Return the byte array
   }

   override fun analyze(image: ImageProxy) {

       val buffer = image.planes[0].buffer
       val data = buffer.toByteArray()
       val pixels = data.map { it.toInt() and 0xFF }
       val luma = pixels.average()

       listener(luma)

       image.close()
   }
}

//调用
imageAnalyzer = ImageAnalysis.Builder()
   .build()
   .also {
       it.setAnalyzer(cameraExecutor, LuminosityAnalyzer { luma ->
           Log.d(TAG, "Average luminosity: $luma")
       })
   }

官方使用示例：https://codelabs.developers.google.com/codelabs/camerax-getting-started/#0