Increasing animation rate in keyframe method apparently disables the feature - animation

Question

I have searched and found nothing. I am trying to get a simple bouncing ball to speed up on a continuous basis. The code below does not speed the ball up at all (even with a mouse click), however the getRate() property does increase as expected. If I comment out the increaseSpeed() method call in moveBall() the mouse click will speed up the ball.
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
public class MyApp extends Application {
#Override
public void start(Stage primaryStage) {
Bounce bouncePane = new Bounce();
bouncePane.setOnMousePressed(e -> bouncePane.increaseSpeed());
Scene scene = new Scene(bouncePane, 250, 150);
primaryStage.setTitle("Bouncing Ball");
primaryStage.setScene(scene);
primaryStage.show();
bouncePane.requestFocus();
}
}
public class Bounce extends Pane {
public final double rad = 25;
private double x = rad, y = rad;
private double dx = 1, dy = 1;
private Circle ball = new Circle(x, y, rad);
private Timeline anim;
public Bounce() {
ball.setFill(Color.BLUE);
getChildren().add(ball);
anim = new Timeline(
new KeyFrame(Duration.millis(50), e -> moveBall()));
anim.setCycleCount(Timeline.INDEFINITE);
anim.play();
}
public void increaseSpeed() {
anim.setRate(anim.getRate() + 0.5);
System.out.println(anim.getRate());
}
protected void moveBall() {
if (x < rad || x > getWidth() - rad) {
dx *= -1;
}
if (y < rad || y > getHeight() - rad) {
dy *= -1;
}
x += dx;
y += dy;
ball.setCenterX(x);
ball.setCenterY(y);
increaseSpeed();
}
}

Answer 1

Your application actually works (kinda)
If you set the duration of your KeyFrame to Duration.millis(1_000) instead of Duration.millis(50), then you will see the animation speed up (well up to a factor of 1_000/60).
Huh? What's going on
By default JavaFX is capped at 60 frames per second. The key frames in your timeline will not be invoked any more often than that, no matter what you set the playback rate to. Because in your example you set the initial duration of the animation to 50 milliseconds, then increase rate by 50 percent of the original rate in each frame, the animation callback for the key frame quickly (in a fraction of time imperceptible to the human eye) reaches the maximum frame rate of 60 frames per second and once it does that, you can't run it any faster.
What you can do
For this kind of problem, perhaps don't rely on animation playback rate to control the speed of your object. Instead, implement a "game loop" using an AnimationTimer and associate a velocity with your objects and move the object to the required position based upon the loop such as is done in this AnimationTimerTest by JamesD.