CameraX 用例的输出分为两部分:缓冲区和转换信息。缓冲区是一个字节数组,转换信息指定了缓冲区在显示给最终用户之前应如何裁剪和旋转。如何应用转换取决于缓冲区的格式。
ImageCapture
对于 ImageCapture
用例,裁剪矩形缓冲区会在保存到磁盘之前应用,并且旋转信息会保存到 Exif 数据中。应用无需执行额外操作。
预览
对于 Preview
用例,您可以通过调用 SurfaceRequest.setTransformationInfoListener()
来获取转换信息。每次转换更新时,调用方都会收到一个新的 SurfaceRequest.TransformationInfo
对象。
如何应用转换信息取决于 Surface
的来源,通常这不是一件简单的事。如果目标只是简单地显示预览,请使用 PreviewView
。PreviewView
是一个自定义视图,它会自动处理转换。对于高级用途,例如需要使用 OpenGL 编辑预览流时,请查看 CameraX 核心测试应用中的代码示例。
转换坐标
另一个常见任务是处理坐标而不是缓冲区,例如在预览中在检测到的脸部周围绘制一个框。在这种情况下,您需要将检测到的脸部的坐标从图像分析转换到预览。
以下代码段创建了一个矩阵,用于将图像分析坐标映射到 PreviewView
坐标。要使用 Matrix
转换 (x, y) 坐标,请参阅 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; }