Timeline for parabolic trajectory in JavaFX

Question

I'm sorry, but I continue not understanding. My problem is I know nothing about physics but my teacher assigned to me this project.

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();
}

I'm at a standstill. Please, help meeee

I'm trying to shoot a bullet from a cannon(cannone_im is the ImageView of the cannone) , but I have problems whit the KeyValue and I can't move on — Bruno Battaglia, Jun 25 '16 at 18:35
So, after the update, what is the actual question you are asking? — James_D, Jun 25 '16 at 19:43
You right, I was confusing two time. I've update again the post. I ask you the last help! Thank you! — Bruno Battaglia, Jun 25 '16 at 22:56
Your updates are substantially changing the question, so that the answer that was provided is no longer relevant to the question. If you have a new question, please post a new question. — James_D, Jun 25 '16 at 23:20

score 5 · Accepted Answer · edited May 23 '17 at 12:08

In a KeyValue, the first parameter should be a WritableValue, e.g. circle.centerXProperty(), which represents the initial coordinate, say x. The second parameter should be a type compatible value, in this case the x coordinate toward which the projectile should move. As the timeline plays, the WritableValue will be updated accordingly. Add a second KeyValue to drive the y coordinate.

In the first example seen here, three instances of KeyValue move a figure from it's initial position to its destination position, which is size units away along each coordinate axis. In this related example, a figure moves form point p1 to p2.

In the example below, a Circle moves parallel to the x axis between 100 and 500. At the same time, that same Circle moves parallel to the y axis between 300 and 100 following the curve() defined by the parabola y = –4(x – ½)² + 1, which has vertex (½, 1) and x intercepts at 0 and 1. This implementation of curve() models a parabolic path on a unit square, as required by the curve() API. You can change the angle of elevation by changing the ratio of height to width in the keys frames, e.g.

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);
    }

}

Yes, there is a [constructor](http://docs.oracle.com/javase/8/javafx/api/javafx/animation/KeyValue.html#KeyValue-javafx.beans.value.WritableValue-T-) that doesn't take an interpolator. — James_D, Jun 25 '16 at 19:07
I've updated the question. When I try to shoot the bullet clicking on the button "shoot", I just see the circle for a while. I don't see the entire curve. I also try to write " circle.setTranslateX(x1); circle.setTranslateY(y1);" — Bruno Battaglia, Jun 25 '16 at 19:32
Sorry, I was mistaken about the best `WritableValue` for this usage; I've added an example using an `Interpolator` that defines a parabolic trajectory. — trashgod, Jun 26 '16 at 03:57
I've elaborated above on your [original question](http://stackoverflow.com/revisions/38031582/1) asking for help with parameters and a parabolic path. For help with the [ballistic trajectory of a projectile](https://en.wikipedia.org/wiki/Trajectory_of_a_projectile), please see [ask] a new question; for reference, your implementation of `curve()` must also map to a unit square; a [mcve] will likely get more attention; also consider a [`PathTransition`](https://docs.oracle.com/javase/8/javafx/api/javafx/animation/PathTransition.html) along a suitable `Path`. — trashgod, Jun 30 '16 at 08:23

Timeline for parabolic trajectory in JavaFX

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