SurfaceRequest.TransformationInfo

abstract fun getCropRect(): Rect

Returns the crop rect rectangle.

The returned value dictates how the Surface provided in provideSurface should be displayed. The crop rectangle specifies the region of valid pixels in the buffer, using coordinates from (0, 0) to the (width, height) of getResolution. The caller should arrange the UI so that only the valid region is visible to app users.

If Preview is configured with a ViewPort, this value is calculated based on the configuration of ViewPort; if not, it returns the full rect of the buffer. For code sample on how to apply the crop rect, please see FIT.

abstract fun getRotationDegrees(): Int

Returns the rotation needed to transform the output from sensor to the target rotation.

This is a clockwise rotation in degrees that needs to be applied to the sensor buffer. The rotation will be determined by CameraCharacteristics, setTargetRotation and setTargetRotation. This value is useful for transforming coordinates across use cases.

This value is most useful for transforming coordinates across use cases, e.g. in preview, highlighting a pattern detected in image analysis. For correcting the preview itself, usually the source of the Surface handles the rotation without needing this value. For SurfaceView, it automatically corrects the preview to match the display rotation. For TextureView, the only additional rotation needed is the display rotation. For detailed example, please check out the source code of PreviewView in androidx.camera .view artifact.

abstract fun getSensorToBufferTransform(): Matrix

Returns the sensor to image buffer transform matrix.

The value is a mapping from sensor coordinates to buffer coordinates, which is, from the rect of SENSOR_INFO_ACTIVE_ARRAY_SIZE to the rect defined by (0, 0, #getResolution#getWidth(), #getResolution#getHeight()). The matrix can be used to map the coordinates from one UseCase to another. For example, detecting face with ImageAnalysis, and then highlighting the face in Preview.

Code sample

 // Get the transformation from sensor to effect input.
 Matrix sensorToEffect = surfaceRequest.getSensorToBufferTransform();
 // Get the transformation from sensor to ImageAnalysis.
 Matrix sensorToAnalysis = imageProxy.getSensorToBufferTransform();
 // Concatenate the two matrices to get the transformation from ImageAnalysis to effect.
 Matrix analysisToEffect = Matrix()
 sensorToAnalysis.invert(analysisToEffect);
 analysisToEffect.postConcat(sensorToEffect);

abstract fun hasCameraTransform(): Boolean

Whether the Surface contains the camera transform.

When the Surface is connected to the camera directly, camera writes the camera orientation value to the Surface. For example, the value can be retrieved via getTransformMatrix. Android components such as TextureView and SurfaceView use the value to transform the output. When the Surface is not connect to the camera directly, for example, when it was copied with OpenGL, the Surface will not contain the camera orientation value.

The app may need to transform the UI differently based on this flag. If this value is true, the app only needs to apply the Surface transformation; otherwise, the app needs to apply the value of getRotationDegrees. For example, if the preview is displayed in a TextureView:

int rotationDegrees;
if (surfaceRequest.hasCameraTransform()) {
  switch (textureView.getDisplay().getRotation()) {
    case Surface.ROTATION_0:
      rotationDegrees = 0;
      break;
    case Surface.ROTATION_90:
      rotationDegrees = 90;
      break;
    case Surface.ROTATION_180:
      rotationDegrees = 180;
      break;
    case Surface.ROTATION_270:
      rotationDegrees = 270;
      break;
    }
} else {
  rotationDegrees = transformationInfo.getRotationDegrees();
}
Matrix textureViewTransform = new Matrix();
textureViewTransform.postRotate(rotationDegrees);
textureView.setTransform(textureViewTransform);

abstract fun isMirroring(): Boolean

Returns whether the buffer should be mirrored.

This flag indicates whether the buffer needs to be mirrored across the vertical axis. For example, for front camera preview, the buffer should usually be mirrored. The mirroring should be applied after the getRotationDegrees is applied.