轉換輸出內容

CameraX 用途有兩項輸出內容:緩衝區和轉換資訊。緩衝區為位元組陣列,轉換資訊則說明在向使用者顯示前,該如何裁剪及旋轉緩衝區。套用轉換資訊的方式視緩衝區格式而定。

ImageCapture

如果是 ImageCapture 用途,系統會先套用裁剪矩形緩衝區,再儲存至磁碟,並將旋轉資訊儲存在 EXIF 資料中。應用程式不需採取任何額外動作。

Preview

如果是 Preview 用途,可以呼叫 SurfaceRequest.setTransformationInfoListener() 來取得轉換資訊。轉換資訊每次更新時,呼叫端都會收到新的 SurfaceRequest.TransformationInfo 物件。

套用轉換資訊的方式取決於 Surface 的來源,且通常至關重要。如果目標只是要顯示預覽畫面,請使用 PreviewViewPreviewView 是會自動處理轉換資訊的自訂檢視畫面。如果是需要編輯預覽串流 (例如使用 OpenGL) 的進階用途,請參閱 CameraX 核心測試應用程式中的程式碼範例。

轉換座標

另一項常見工作是處理座標而非緩衝區,例如在預覽畫面上偵測到的臉孔周圍繪製方塊。在這類情況下,需要將偵測到的臉孔座標,從圖像分析轉換至預覽畫面。

以下程式碼片段會建立矩陣,將圖像分析座標對應至 PreviewView 座標。如要使用 Matrix 轉換 (x, y) 座標,請參閱 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;
}