变换输出

CameraX 用例的输出有两部分：缓冲区和变换信息。缓冲区是一个字节数组，变换信息描述了在向最终用户显示之前如何裁剪和旋转缓冲区。变换的应用方式取决于缓冲区的格式。

ImageCapture

对于ImageCapture用例，裁剪矩形缓冲区在保存到磁盘之前应用，旋转信息则保存在 Exif 数据中。应用无需执行任何其他操作。

预览

对于Preview用例，您可以通过调用SurfaceRequest.setTransformationInfoListener()来获取变换信息。每次变换更新时，调用方都会收到一个新的SurfaceRequest.TransformationInfo对象。

如何应用变换信息取决于Surface的来源，通常并非易事。如果目标只是显示预览，请使用PreviewView。PreviewView是一个自定义视图，会自动处理变换。对于高级用法（例如使用 OpenGL 编辑预览流），请查看CameraX 核心测试应用中的代码示例。

变换坐标

另一个常见任务是处理坐标而不是缓冲区，例如在预览中绘制围绕检测到的面部的方框。在这种情况下，需要将检测到的面部的坐标从图像分析变换到预览。

以下代码片段创建一个矩阵，该矩阵将图像分析坐标映射到PreviewView坐标。要使用Matrix变换 (x, y) 坐标，请参见Matrix.mapPoints()。

Kotlin

fun getCorrectionMatrix(imageProxy: ImageProxy, previewView: PreviewView) : Matrix {
   val cropRect = imageProxy.cropRect
   val rotationDegrees = imageProxy.imageInfo.rotationDegrees
   val matrix = Matrix()

   // A float array of the source vertices (crop rect) in clockwise order.
   val source = floatArrayOf(
       cropRect.left.toFloat(),
       cropRect.top.toFloat(),
       cropRect.right.toFloat(),
       cropRect.top.toFloat(),
       cropRect.right.toFloat(),
       cropRect.bottom.toFloat(),
       cropRect.left.toFloat(),
       cropRect.bottom.toFloat()
   )

   // A float array of the destination vertices in clockwise order.
   val destination = floatArrayOf(
       0f,
       0f,
       previewView.width.toFloat(),
       0f,
       previewView.width.toFloat(),
       previewView.height.toFloat(),
       0f,
       previewView.height.toFloat()
   )

   // The destination vertexes need to be shifted based on rotation degrees. The
   // rotation degree represents the clockwise rotation needed to correct the image.

   // Each vertex is represented by 2 float numbers in the vertices array.
   val vertexSize = 2
   // The destination needs to be shifted 1 vertex for every 90° rotation.
   val shiftOffset = rotationDegrees / 90 * vertexSize;
   val tempArray = destination.clone()
   for (toIndex in source.indices) {
       val fromIndex = (toIndex + shiftOffset) % source.size
       destination[toIndex] = tempArray[fromIndex]
   }
   matrix.setPolyToPoly(source, 0, destination, 0, 4)
   return matrix
}

Java

Matrix getMappingMatrix(ImageProxy imageProxy, PreviewView previewView) {
   Rect cropRect = imageProxy.getCropRect();
   int rotationDegrees = imageProxy.getImageInfo().getRotationDegrees();
   Matrix matrix = new Matrix();

   // A float array of the source vertices (crop rect) in clockwise order.
   float[] source = {
       cropRect.left,
       cropRect.top,
       cropRect.right,
       cropRect.top,
       cropRect.right,
       cropRect.bottom,
       cropRect.left,
       cropRect.bottom
   };

   // A float array of the destination vertices in clockwise order.
   float[] destination = {
       0f,
       0f,
       previewView.getWidth(),
       0f,
       previewView.getWidth(),
       previewView.getHeight(),
       0f,
       previewView.getHeight()
   };

   // The destination vertexes need to be shifted based on rotation degrees.
   // The rotation degree represents the clockwise rotation needed to correct
   // the image.

   // Each vertex is represented by 2 float numbers in the vertices array.
   int vertexSize = 2;
   // The destination needs to be shifted 1 vertex for every 90° rotation.
   int shiftOffset = rotationDegrees / 90 * vertexSize;
   float[] tempArray = destination.clone();
   for (int toIndex = 0; toIndex < source.length; toIndex++) {
       int fromIndex = (toIndex + shiftOffset) % source.length;
       destination[toIndex] = tempArray[fromIndex];
   }
   matrix.setPolyToPoly(source, 0, destination, 0, 4);
   return matrix;
}