Thread: When I decrease the Speed of a Timeline animation I get a Negative rateProperty

Hello everybody.

I've created my own particular version of the Java FX program for the Bouncing Ball.

I was testing the method decreaseSpeed() in order to try to understand the variation of the decrease of the rateProperty of the Timeline Animation.

The increase of the speed is done using the UP key in the Keyboard.

The decrease of the speed is done using the DOWN key in the Keyboard.

The first thing I've discovered is that the Increase/Decrease of the rateProperty of the Timeline Animation is not uniform.

For example a uniform increase/decrease (using only integers as simplification would be)

1 -> 2 -> 3 -> 4

4 -> 3 -> 2 -> 1

In this example every time I would increase I would increase it by adding one.

If I was decreasing I would decrease it by subtracting one.

In my program the rate is a double but is not uniform.

In my first run decrease I get:


The current rate is 1.100000000000001
The current rate is 1.0000000000000009
The current rate is 0.9000000000000009
The current rate is 0.8000000000000009
The current rate is 0.700000000000001
The current rate is 0.600000000000001
The current rate is 0.500000000000001
The current rate is 0.400000000000001
The current rate is 0.30000000000000104
The current rate is 0.20000000000000104
The current rate is 0.10000000000000103


Then I increased the rate a little, and after that I decreased it again, and I got this:


The current rate is 1.0999999999999999
The current rate is 0.9999999999999999
The current rate is 0.8999999999999999
The current rate is 0.7999999999999999
The current rate is 0.7
The current rate is 0.6
The current rate is 0.5
The current rate is 0.4
The current rate is 0.30000000000000004
The current rate is 0.20000000000000004
The current rate is 0.10000000000000003


As you can see the values are different in the two times.

But that is not why I'm making this post.

When I decrease the rate the Rate reaches 0 and if, after that, I try to decrease it again it stays 0.

But, before the rateProperty gets to Zero, I always get a Negative number before it.

So, in the next lines, there are two examples, and in both Examples I get a Negative rate Property.



I've Increased the Rate Property before this

The current rate is 2.8000000000000016
The current rate is 2.7000000000000015
The current rate is 2.6000000000000014
The current rate is 2.5000000000000013
The current rate is 2.4000000000000012
The current rate is 2.300000000000001
The current rate is 2.200000000000001
The current rate is 2.100000000000001
The current rate is 2.000000000000001
The current rate is 1.9000000000000008
The current rate is 1.8000000000000007
The current rate is 1.7000000000000006
The current rate is 1.6000000000000005
The current rate is 1.5000000000000004
The current rate is 1.4000000000000004
The current rate is 1.3000000000000003
The current rate is 1.2000000000000002
The current rate is 1.1
The current rate is 1.0
The current rate is 0.9
The current rate is 0.8
The current rate is 0.7000000000000001
The current rate is 0.6000000000000001
The current rate is 0.5000000000000001
The current rate is 0.40000000000000013
The current rate is 0.30000000000000016
The current rate is 0.20000000000000015
The current rate is 0.10000000000000014
The current rate is 1.3877787807814457E-16

This is a negative current rate

The current rate is -0.09999999999999987


The current rate is 0.0
The current rate is 0.0
The current rate is 0.0

I've Increased the Rate Property before this

The current rate is 2.3000000000000007
The current rate is 2.2000000000000006
The current rate is 2.1000000000000005
The current rate is 2.0000000000000004
The current rate is 1.9000000000000004
The current rate is 1.8000000000000003
The current rate is 1.7000000000000002
The current rate is 1.6
The current rate is 1.5
The current rate is 1.4
The current rate is 1.2999999999999998
The current rate is 1.1999999999999997
The current rate is 1.0999999999999996
The current rate is 0.9999999999999997
The current rate is 0.8999999999999997
The current rate is 0.7999999999999997
The current rate is 0.6999999999999997
The current rate is 0.5999999999999998
The current rate is 0.4999999999999998
The current rate is 0.3999999999999998
The current rate is 0.2999999999999998
The current rate is 0.19999999999999982
The current rate is 0.09999999999999981

This is a negative current rate

The current rate is -1.942890293094024E-16


The current rate is 0.0
The current rate is 0.0
The current rate is 0.0


Can someone please explain me why this happens and if it is sort of an Overflow / Underflow ?

Thank you,

Rogério

Hello Norm.

Here you have the code.

This is the code for the class BallPaneOldVersion:

 
 
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package Chapter15.Section15dot12BouncingBall.OldVersion;
 
/**
 *
 * @author Rogerio Biscaia
 */
 
 
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.beans.property.DoubleProperty;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.util.Duration;
 
 
 
 
public class BallPaneOldVersion extends Pane {
 
    /*
    Data fields
    */
 
    public final double RADIUS = 20;
 
    private double x = RADIUS;
 
    private double y = RADIUS;
 
    private double dx = 1;
 
    private double dy = 1;
 
    private Circle circle = new Circle(x, y, RADIUS);
 
    private Timeline animation;
 
 
    /*
    No-arg Constructor
    */
 
    public BallPaneOldVersion() {
 
        circle.setFill( Color.GREEN );
 
        getChildren().clear();
 
        getChildren().add( circle );
 
        /*
        Create an
        animation for
        moving the ball
        */
 
        animation = new Timeline( new KeyFrame( Duration.millis( 50 ), e -> moveBall() ) ); //end of animation = new Timeline();
 
        animation.setCycleCount( Timeline.INDEFINITE );
 
        animation.play();
 
    } //end of the constructor public BallPane()
 
 
    public void play() {
 
        animation.play();
 
    }
 
 
    public void pause() {
 
        animation.pause();
 
    }
 
 
    public void increaseSpeed() {
 
        double currentRate;
 
        currentRate = rateProperty().doubleValue();
 
 
        //System.out.println( "The current rate before increase is " + currentRate + "\nIncreasing Speed" );
 
 
        animation.setRate( animation.getRate() + 0.1 );
 
 
    }
 
 
    public void decreaseSpeed() {
 
        double currentRate;
 
 
        currentRate = rateProperty().doubleValue();
 
 
        System.out.println( "The current rate before decrease is " + currentRate + "\nDecreasing Speed" );
 
 
        animation.setRate( 
        animation.getRate() > 0 ? animation.getRate() - 0.1 : 0 );
 
 
    }
 
 
 
 
 
    public DoubleProperty rateProperty() {
 
        return animation.rateProperty();
 
    }
 
 
    protected void moveBall() {
 
 
        /*
        Check boundaries
        */
 
        if( x < RADIUS || x > getWidth() - RADIUS ) {
 
            dx *= -1; //Change ball move direction
 
        }
 
 
        if( y < RADIUS || y > getHeight() - RADIUS ) {
 
            dy *= -1; //Change ball move direction
 
        }
 
 
        /*
        Adjust ball position
        */
 
 
 
        x += dx;
 
        y += dy;
 
        circle.setCenterX( x );
 
        circle.setCenterY( y );
 
 
 
    } //end of the method protected void moveBall()
 
 
} //end of the class BallPaneOldVersion

And this is the code for the class BounceBallControlOldVersion

 
 
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package Chapter15.Section15dot12BouncingBall.OldVersion;
 
/**
 *
 * @author Rogerio Biscaia
 */
 
 
 
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
 
 
 
 
public class BounceBallControlOldVersion extends Application {
 
 
    @Override
    public void start(Stage primaryStage) throws Exception {
 
 
        BallPaneOldVersion ballPane = new BallPaneOldVersion(); //Create a ball pane
 
 
        /*
        Pause and resume animation
        */
 
        ballPane.setOnMousePressed( e -> ballPane.pause() );
 
        ballPane.setOnMouseReleased( e -> ballPane.play() );
 
 
        /*
        Increase and decrease animation
        */
 
        ballPane.setOnKeyPressed( e -> { 
 
            if( e.getCode() == KeyCode.UP ) {
 
                ballPane.increaseSpeed();
 
            } else if( e.getCode() == KeyCode.DOWN ) {
 
                ballPane.decreaseSpeed();
 
            }
 
 
        } ); //end of  ballPane.setOnKeyPressed( e -> {} )
 
 
        /*
        Create a scene and
        place it in the stage
        */
 
        Scene scene = new Scene(ballPane, 250, 150);
 
        primaryStage.setTitle( "BounceBallControl" ); //Set the stage title
 
        primaryStage.setScene(scene); //Place the scene in the stage
 
        primaryStage.show(); //Display the stage
 
 
        /*
        Must request
        focus after the
        primary stage is displayed
        */
 
        ballPane.requestFocus();
 
 
 
    } //end of the method public void start(Stage primaryStage)
 
 
 
 
    /*
    The main method is only needed for the IDE with
    limited JavaFX support.
    Not needed for running from the
    command line
    */
 
    public static void main(String[] args) {
 
        Application.launch(args);
 
    }
 
 
 
 
} //end of the class BounceBallControlOldVersion

Thank you, Norm.

Rogério

Hello Norm.

Thank you for your answer.

I've already solved that problem using a different approach.

If the rate is greater than 0.1 it decreases it by 0.1, else it sets the rate as 0.0.

That allowed me to solve another problem.

I call that problem the "Wormhole" problem.

Before, when I decreased the rateProperty to 0.0 the ball would stop.

But after that, when I increased the rate the Ball would continue to move from a different position in the pane and not continue to move from the position where it was "frozen" before.

It is like if the ball would stop "frozen" at a certain position, it was swallowed by a Wormhole and it appears later moving in a different position.

Now the ball only moves if the program is running and the rate is greater than 0.1.

Now the ball continues moving from the previous position where it was "frozen".

Thank you again.

Rogério

Hello Norm.

First of all thank you for your previous answer.

I did not want to ignore your answer.

I think I understood your previous answers.

As for your last answer of yesterday, yes, the Timeline is calling the moveBall method every 50 milliseconds.

I will add these extra print statements in my New Version.

Thank you again, Norm

Rogério

Hello Norm.

Yes you are Right.

There are several times that the x and y are updated in the same millisecond.

For example in the date:

2024-09-11 16:40:19.778

778 is the milliseconds.

The x and y were updated 5 times.




The x and y were updated
New x is 123.0 and new y is 99.0
2024-09-11 16:40:05.450
The x and y were updated
New x is 124.0 and new y is 100.0
2024-09-11 16:40:05.474
The current rate before decrease is -0.09999999999999987
Decreasing Speed
The current rate after decrease is 0.0
The current rate before decrease is 0.0
Decreasing Speed
The current rate after decrease is 0.0
The current rate before decrease is 0.0
Decreasing Speed
The current rate after decrease is 0.0
The current rate before decrease is 0.0
Decreasing Speed
The current rate after decrease is 0.0



Before this, I increased the rate



The x and y were updated
New x is 125.0 and new y is 101.0
2024-09-11 16:40:19.778
The x and y were updated
New x is 126.0 and new y is 102.0
2024-09-11 16:40:19.778
The x and y were updated
New x is 127.0 and new y is 103.0
2024-09-11 16:40:19.778
The x and y were updated
New x is 128.0 and new y is 104.0
2024-09-11 16:40:19.778
The x and y were updated
New x is 129.0 and new y is 105.0
2024-09-11 16:40:19.778



The x and y were updated
New x is 130.0 and new y is 106.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 131.0 and new y is 107.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 132.0 and new y is 108.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 133.0 and new y is 109.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 134.0 and new y is 110.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 135.0 and new y is 111.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 136.0 and new y is 112.0
2024-09-11 16:40:19.779
The x and y were updated
New x is 137.0 and new y is 113.0
2024-09-11 16:40:19.779


The x and y were updated
New x is 138.0 and new y is 114.0
2024-09-11 16:40:19.780



So, if I understood well when the rate decreases to 0, the program makes a lot of updates to the x and y, but sort of pauses the execution of those updates.

When the rate increases from 0 the program makes all the updates of x and y that were previously sort of paused, but makes it all at once.

Thank you, Norm

Rogério

Thank you, Norm.