JavaFX中抛物线轨迹的时间线

Question

抱歉，我仍然不明白。我的问题是我对物理学一无所知，但我的老师指派给我这个项目。

private void shoot() {        
    Group group = new Group();
    double angle = cannon.getRotate();
    double speed = slider.getValue();
    double x = cannon.getLayoutX();
    double y = cannon.getLayoutY();
    double v0X = Math.cos(angle)*speed;
    double voY = Math.sin(angle)*speed;        
    Circle c = new Circle(x, y, 8, Color.BLACK);
    /*t is the time, but I don't know its 
    value or has it the same value of the KeyFrame duration? */
    double x2 = x + voX*t;
    double y2 = y + v0Y * t - 0.5 * gravity * t * t;
    Line l = new Line(x, y, x2, y2);
    l.setStroke(Color.BLACK);
    group.getChildren().addAll(c, l);
    final Timeline timeline = new Timeline();
    KeyValue xKV = new KeyValue(c.centerXProperty(), x2);
    KeyValue yKV = new KeyValue(c.centerYProperty(), y2 , new Interpolator() {
        @Override
        //Maybe I need I splite, not a curve (?)
        protected double curve(double t) {  
       //thisshould be trajectory's formula              
           return Math.tan(angle) * x*-(gravity/(2*speed*Math.cos(angle)))*x*x;                
        }
    });
    KeyFrame xKF = new KeyFrame(Duration.millis(2000), xKV);
    KeyFrame yKF = new KeyFrame(Duration.millis(2000), yKV);
    timeline.getKeyFrames().addAll(xKF, yKF);
    timeline.play();
}

我处于停滞状态。请帮忙

Answer 1

在a中KeyValue，第一个参数应为a
WritableValue，例如circle.centerXProperty()，代表初始坐标，例如x。第二个参数应该是类型兼容的值，在这种情况下x，就是射弹应向其移动的坐标。随着时间线播放，WritableValue将会相应更新。添加一秒钟KeyValue以驱动y坐标。

在此处看到的第一个示例中，三个实例KeyValue将图形从其初始位置移动到其目的地位置，该位置是size沿每个坐标轴的单位。在此相关示例中，图形将形状点移动p1到p2。

在下面的例子中，Circle移动平行于x间轴100和500。同时，它们Circle平行于抛物线 y = –4（ x –½）2
+1 html" target="_blank">定义的y轴之间300并100跟随其移动的轴，其顶点（1 / 2，1）且 x
在0和1处相交。根据API的要求，在单位正方形上实现抛物线路径模型的实现。您可以通过在关键帧中更改高度与宽度的比率来更改仰角，例如curve() __curve()``curve()

KeyValue xKV = new KeyValue(c.centerXProperty(), 200);
KeyValue yKV = new KeyValue(c.centerYProperty(), 0, new Interpolator() {…});

import javafx.animation.Interpolator;
import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.stage.Stage;
import javafx.util.Duration;

/**
 * @see https://stackoverflow.com/a/38031826/230513
 */
public class Test extends Application {

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Test");
        Group group = new Group();
        Scene scene = new Scene(group, 600, 350);
        scene.setFill(Color.BLACK);
        primaryStage.setScene(scene);
        primaryStage.show();
        Circle c = new Circle(100, 300, 16, Color.AQUA);
        Line l = new Line(100, 300, 500, 300);
        l.setStroke(Color.AQUA);
        group.getChildren().addAll(c, l);
        final Timeline timeline = new Timeline();
        timeline.setCycleCount(Timeline.INDEFINITE);
        timeline.setAutoReverse(false);
        KeyValue xKV = new KeyValue(c.centerXProperty(), 500);
        KeyValue yKV = new KeyValue(c.centerYProperty(), 100, new Interpolator() {
            @Override
            protected double curve(double t) {
                return -4 * (t - .5) * (t - .5) + 1;
            }
        });
        KeyFrame xKF = new KeyFrame(Duration.millis(2000), xKV);
        KeyFrame yKF = new KeyFrame(Duration.millis(2000), yKV);
        timeline.getKeyFrames().addAll(xKF, yKF);
        timeline.play();
    }

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

}