StageScaleMode scaleMode

Gets and sets the scale mode of this Stage. You can choose between four different modes defined in StageScaleMode.

Source 

StageScaleMode get scaleMode => _stageScaleMode;
void scaleMode=(StageScaleMode value)

Source 

set scaleMode(StageScaleMode value) {
  _stageScaleMode = value;
  _updateCanvasSize();
}