rotationForFrame function

CameraFrameRotation? rotationForFrame({ required int width, required int height, required int sensorOrientation, required bool isFrontCamera, required DeviceOrientation deviceOrientation, })

Compute the rotation needed to present a camera frame upright to an on-device detection model, given the camera's sensor orientation and the device's current physical orientation.

• iOS: assumes the camera plugin pre-rotates the image stream per AVCaptureConnection.videoOrientation (portrait-only path). Returns a rotation only when the device is in portrait and the frame arrived in landscape-sensor layout.
• Android: combined (sensor ± deviceRotation) % 360 formula; the sign depends on front vs. back camera.
• Other platforms (desktop / web): returns null; camera_desktop and the web backend deliver already-upright frames.

Callers typically pass image.width / image.height from a CameraImage, the camera's sensorOrientation (via CameraDescription.sensorOrientation), and the effective device orientation (via CameraController.value.deviceOrientation on mobile, or a fallback based on MediaQuery when the controller is still initializing).

Implementation

CameraFrameRotation? rotationForFrame({
  required int width,
  required int height,
  required int sensorOrientation,
  required bool isFrontCamera,
  required DeviceOrientation deviceOrientation,
}) {
  if (defaultTargetPlatform == TargetPlatform.iOS) {
    final bool isPortrait =
        deviceOrientation == DeviceOrientation.portraitUp ||
        deviceOrientation == DeviceOrientation.portraitDown;
    if (!isPortrait) return null;
    if (height >= width) return null;
    if (sensorOrientation == 90) return CameraFrameRotation.cw90;
    if (sensorOrientation == 270) return CameraFrameRotation.cw270;
    return null;
  }

  if (defaultTargetPlatform == TargetPlatform.android) {
    final int deviceRotation = switch (deviceOrientation) {
      DeviceOrientation.portraitUp => 0,
      DeviceOrientation.landscapeLeft => 90,
      DeviceOrientation.portraitDown => 180,
      DeviceOrientation.landscapeRight => 270,
    };

    final int total = isFrontCamera
        ? (sensorOrientation + deviceRotation) % 360
        : (sensorOrientation - deviceRotation + 360) % 360;

    return switch (total) {
      90 => CameraFrameRotation.cw90,
      180 => CameraFrameRotation.cw180,
      270 => CameraFrameRotation.cw270,
      _ => null,
    };
  }

  return null;
}