如何使用Slider动态更改JavaFX AnimationTimer的速度？

Question

I'm working on a variant of the Conway's Game of Life called Wireworld, and I want to have a slider control so the user can change the speed of the simulation at will. I think I just have a simple math hiccup, but what I'm doing is getting the difference between the current nano time and the last update, then dividing by 1,000,000,000 (to convert to seconds), and checking to see if it's greater than or equal to the update time (0.016667) divided by the speed slider value (a value between 0.05 and 1.0).

Here is the code as I have it...

new AnimationTimer() {
    private long lastUpdate = 0;

    public void handle(long currentNanoTime) {
        if((double)((currentNanoTime - lastUpdate) / 1000000000) >= (updateTime / speedSlider.getValue())) {

And then at the end of the update cycle, I change lastUpdate to the value of currentNanoTime.

Is there something wrong with this approach? The animation moves very slow at the default speed of 0.5, and there's no noticeable difference when moving the slider to either extreme.

Answer 1

It seems the problem was where I was casting the two longs in the conditional. Instead of this...

if((double)((currentNanoTime - lastUpdate) / 1000000000) >= (updateTime / speedSlider.getValue())) {

I needed to do this...

if((((double)currentNanoTime - (double)lastUpdate) / 1000000000.0) >= (updateTime / speedSlider.getValue())) {

I suspected this was the problem. The problem being that, like integer division, even if you convert it to a double, the division happens first, so it would be a round number, rather than an accurate floating point number. I guess I just needed to take a break and think about it. Works fine now!