finalizeBitmap method
Stops the recording and returns a TilePicture object.
Implementation
Future<TilePicture> finalizeBitmap() async {
ui.Picture pic = _pictureRecorder!.endRecording();
// unfortunately working with Picture is too slow because we have to render it each time
ui.Image img = await pic.toImage(_size.width.ceil(), _size.height.ceil());
_pictureRecorder = null;
pic.dispose();
TilePicture picture = TilePicture.fromBitmap(img);
return picture;
}