How do I change the speed of an AnimationTimer in JavaFX? - animation

Question

I'm trying to change the speed of an AnimationTimer so the code runs slower, here is the code I have so far:
AnimationTimer timer = new AnimationTimer() {
#Override
public void handle(long now) {
if (upOrDown != 1) {
for (int i = 0; i < 4; i++) {
snakePositionDown[i] = snake[i].getX();
snakePositionDownY[i] = snake[i].getY();
}
snake[0].setY(snake[0].getY() + 25);
for (int i = 1; i < 4; i++) {
snake[i].setX(snakePositionDown[i - 1]);
snake[i].setY(snakePositionDownY[i - 1]);
}
leftOrRight = 2;
upOrDown = 0;
}
}
};
timer.start();
How would I make the AnimationTimer run slower?
Thanks in advance!

Answer 1

You could use a Timeline for this purpose. Adjusting the Timeline.rate property also allows you to update the "speed":
// update once every second (as long as rate remains 1)
Timeline timeline = new Timeline(new KeyFrame(Duration.seconds(1), event -> {
if (upOrDown != 1) {
for (int i = 0; i < 4; i++) {
snakePositionDown[i] = snake[i].getX();
snakePositionDownY[i] = snake[i].getY();
}
snake[0].setY(snake[0].getY() + 25);
for (int i = 1; i < 4; i++) {
snake[i].setX(snakePositionDown[i - 1]);
snake[i].setY(snakePositionDownY[i - 1]);
}
leftOrRight = 2;
upOrDown = 0;
}
}));
timeline.setCycleCount(Animation.INDEFINITE);
timeline.play();
...
// double speed
timeline.setRate(2);

Answer 2

An AnimationTimer's handle() method is invoked on every "pulse" - i.e., every time a frame is rendered. By default, the JavaFX toolkit will attempt to do this 60 times per second, but that is not in any way guaranteed. It can be changed by setting a system property, and it is possible that future versions of JavaFX will attempt to execute pulses more frequently. If the FX Application Thread has a large amount of work to do, then pulses may occur less frequently than the target rate. Consequently, the code in your handle() method needs to account for the amount of time since the last update.
The parameter passed to the handle(...) method represents the current system time in nanoseconds. So a typical way to approach this is:
AnimationTimer h = new AnimationTimer() {
private long lastUpdate; // Last time in which `handle()` was called
private double speed = 50 ; // The snake moves 50 pixels per second
#Override
public void start() {
lastUpdate = System.nanoTime();
super.start();
}
#Override
public void handle(long now) {
long elapsedNanoSeconds = now - lastUpdate;
// 1 second = 1,000,000,000 (1 billion) nanoseconds
double elapsedSeconds = elapsedNanoSeconds / 1_000_000_000.0;
// ...
snake[0].setY(snake[0].getY() + elapsedSeconds * speed);
// ...
lastUpdate = now;
}
}