JavaFx：运行时检查PathTransition的当前位置

Question

I want to get the current position (x,y) of a Circle (javafx.scene.shape.Circle) i am moving via a PathTransition, while the transition is running/happening.

So i need some kind of task, that checks the position of the circle every 50 milliseconds (for example).

I also tried this solution Current circle position of javafx transition which was suggested on Stack Overflow, but i didn't seem to work for me.

Circle projectile = new Circle(Playground.PROJECTILE_SIZE, Playground.PROJECTILE_COLOR);

root.getChildren().add(projectile);

double duration = distance / Playground.PROJECTILE_SPEED;

double xOff = (0.5-Math.random())*Playground.WEAPON_OFFSET;
double yOff = (0.5-Math.random())*Playground.WEAPON_OFFSET;

Line shotLine = new Line(player.getCurrentX(), player.getCurrentY(), aimLine.getEndX() + xOff, aimLine.getEndY() + yOff);

shotLine.setEndX(shotLine.getEndX() + (Math.random()*Playground.WEAPON_OFFSET));

PathTransition pt = new PathTransition(Duration.seconds(duration), shotLine, projectile);

// Linear movement for linear speed
pt.setInterpolator(Interpolator.LINEAR);

pt.setOnFinished(new EventHandler<ActionEvent>() {
    public void handle(ActionEvent event) {
    // Remove bullet after hit/expiration
    projectile.setVisible(false);
    root.getChildren().remove(projectile);
    }
});

projectile.translateXProperty().addListener(new ChangeListener<Number>() {

    @Override
    public void changed(ObservableValue<? extends Number> observable, Number oldValue, Number newValue) {
    double x = collider.getTranslateX() - projectile.getTranslateX();
    double y = collider.getTranslateY() - projectile.getTranslateY();

    double distance = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));

    System.out.println("Distance: "+ distance);

    if (distance < 50) {
        System.out.println("hit");
    }
    }
});

pt.play();

Answer 1

A PathTransition will move a node by manipulating its translateX and translateY properties. (A TranslateTransition works the same way.)

It's hard to answer your question definitively as your code is so incomplete, but if the projectile and collider have the same parent in the scene graph, converting the initial coordinates of the projectile and collider by calling localToParent will give the coordinates in the parent, including the translation. So you can observe the translateX and translateY properties and use that conversion to check for a collision. If they have different parents, you can do the same with localToScene instead and just convert both to coordinates relative to the scene.

Here's a quick SSCCE. Use the left and right arrows to aim, space to shoot:

import javafx.animation.Animation;
import javafx.animation.TranslateTransition;
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.binding.BooleanBinding;
import javafx.geometry.Point2D;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.scene.transform.Rotate;
import javafx.stage.Stage;
import javafx.util.Duration;

public class ShootingGame extends Application {

    @Override
    public void start(Stage primaryStage) {
        final double width = 400 ;
        final double height = 400 ;

        final double targetRadius = 25 ;
        final double projectileRadius = 5 ;

        final double weaponLength = 25 ;

        final double weaponX = width / 2 ;
        final double weaponStartY = height ;
        final double weaponEndY = height - weaponLength ;

        final double targetStartX = targetRadius ;
        final double targetY = targetRadius * 2 ;;

        Pane root = new Pane();
        Circle target = new Circle(targetStartX, targetY, targetRadius, Color.BLUE);
        TranslateTransition targetMotion = new TranslateTransition(Duration.seconds(2), target);
        targetMotion.setByX(350);
        targetMotion.setAutoReverse(true);
        targetMotion.setCycleCount(Animation.INDEFINITE);
        targetMotion.play();

        Line weapon = new Line(weaponX, weaponStartY, weaponX, weaponEndY);
        weapon.setStrokeWidth(5);
        Rotate weaponRotation = new Rotate(0, weaponX, weaponStartY);
        weapon.getTransforms().add(weaponRotation);

        Scene scene = new Scene(root, width, height);
        scene.setOnKeyPressed(e -> {
            if (e.getCode() == KeyCode.LEFT) {
                weaponRotation.setAngle(Math.max(-45, weaponRotation.getAngle() - 2));
            }
            if (e.getCode() == KeyCode.RIGHT) {
                weaponRotation.setAngle(Math.min(45, weaponRotation.getAngle() + 2));
            }
            if (e.getCode() == KeyCode.SPACE) {

                Point2D weaponEnd = weapon.localToParent(weaponX, weaponEndY);

                Circle projectile = new Circle(weaponEnd.getX(), weaponEnd.getY(), projectileRadius);

                TranslateTransition shot = new TranslateTransition(Duration.seconds(1), projectile);
                shot.setByX(Math.tan(Math.toRadians(weaponRotation.getAngle())) * height);
                shot.setByY(-height);
                shot.setOnFinished(event -> root.getChildren().remove(projectile));

                BooleanBinding hit = Bindings.createBooleanBinding(() -> {
                    Point2D targetLocation = target.localToParent(targetStartX, targetY);
                    Point2D projectileLocation = projectile.localToParent(weaponEnd);
                    return (targetLocation.distance(projectileLocation) < targetRadius + projectileRadius) ;
                }, projectile.translateXProperty(), projectile.translateYProperty());

                hit.addListener((obs, wasHit, isNowHit) -> {
                    if (isNowHit) {
                        System.out.println("Hit");
                        root.getChildren().remove(projectile);
                        root.getChildren().remove(target);
                        targetMotion.stop();
                        shot.stop();
                    }
                });

                root.getChildren().add(projectile);
                shot.play();
            }
        });

        root.getChildren().addAll(target, weapon);

        primaryStage.setScene(scene);
        primaryStage.show();
    }

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