JavaFX：动画不动

Question

我正在尝试制作汽车从左向右移动的动画。如果它到达右端，它将重新开始。使用PathTransition可以轻松完成此类动画。但是我必须在动画期间通过UP / DOWN键改变车速。出于某种原因，我无法使用PathTransition。

所以，我正在做一个简单的动画。但在这种情况下，汽车并没有动。有人可以帮助我找到我的错误：

package exercise_15_29;

import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.scene.shape.Polygon;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Duration;
import javafx.animation.KeyFrame;

public class Exercise_15_29 extends Application {
    static Group car = new Group();
    Circle wheel1 = new Circle(15, 95, 5);
    Circle wheel2 = new Circle(35, 95, 5);
    Polygon body1 = new Polygon();
    Rectangle body2 = new Rectangle(0.0, 80.0, 50, 10);
    Line path = new Line(0, 90, 500, 90);

    int speed = 100;
    boolean play = true;

    public static void main(String[] args) {
        launch(args);
    }

    public static void moveCar(){
         if(car.getLayoutX() == 500)
            car.setTranslateX(-500);
         else
            car.setTranslateX(10);
    }

    @Override
    public void start(Stage primaryStage) {

        body1.getPoints().addAll(new Double[]{
                10.0, 80.0,
                20.0, 70.0,
                30.0, 70.0,
                40.0, 80.0
        });
        body1.setFill(Color.BLUE);
        body2.setFill(Color.SKYBLUE);
        path.setVisible(false);

        car.getChildren().addAll(wheel1, wheel2, body1, body2);

        Timeline animation = new Timeline(new KeyFrame(Duration.millis(speed),e -> moveCar()));
        animation.setCycleCount(Timeline.INDEFINITE);
        animation.play();

        Pane root = new Pane();
        root.getChildren().add(car);
        root.getChildren().add(path);

        Scene scene = new Scene(root, 500, 100);

        scene.addEventFilter(KeyEvent.KEY_PRESSED, e -> {
            if (e.getCode() == KeyCode.P) {
                if (play)
                    animation.pause();
                else
                    animation.play();
                play = !play;
            }
        });
        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();

        scene.setOnKeyPressed(e -> {
            if (e.getCode() == KeyCode.UP)
                animation.setRate(animation.getRate() + 0.1);
            else if (e.getCode() == KeyCode.DOWN){
                animation.setRate(
                animation.getRate() > 0 ? animation.getRate() - 0.1 : 0);        
            }
        });
    }

}