如何在Flutter中以编程方式更改Rive/Flare中渐变填充的开始/结束位置？

dependencies:
  flare_flutter: ^2.0.0

FlareActor(
  "assets/animation.flr",
  animation: "animation_name",
)

FlareController flareController = FlareController();

class FlareController extends FlareControls {
  Animation<double> gradientStartAnimation;
  Animation<double> gradientEndAnimation;

  @override
  void initialize(FlutterActorArtboard artboard) {
    gradientStartAnimation = artboard.getAnimation("gradient_start");
    gradientEndAnimation = artboard.getAnimation("gradient_end");
  }

  void setGradientPosition(double start, double end) {
    gradientStartAnimation.apply(start);
    gradientEndAnimation.apply(end);
  }
}

FlareActor(
  "assets/animation.flr",
  animation: "animation_name",
  controller: flareController,
)

flareController.setGradientPosition(0.2, 0.8);