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javatimedeltananotime

(Delta time) Getting 60 updates a second in java

I've seen this code several times.

long lastTime = System.nanoTime();
final double ticks = 60D;
double ns = 1000000000 / ticks;    
double delta = 0;

The code above takes the System time and stores it to lastTime. The 60 ticks should equate to the number of times to update per second.

while(running){
    long now = System.nanoTime();
    delta += (now - lastTime) / ns;
    lastTime = now;
    if(delta >= 1){
        tick();
        delta--;
    }

It takes now and subtracts lastTime, then converts it to nanoseconds/60. Is there some guarantee that the difference in time between now and lastTime to nano over 60 will cause delta to be greater than or equal to 1, 60 times per second? I can't understand why tick(); will run around 60 times per second. From my calculation every time the loop runs delta increases by 0.0025 or so.

Solution

  • Without knowing what's in tick(), I can't be sure, but I'd guess that it also uses 60D to attempt to sleep for about the correct amount of time? So: no, there's isn't a guarantee, which is what this code is there to fix.

    It's saying "If tick() slept for less than a tick, then don't do anything; if it slept by a tick or more, tick once".

    Presumably, if ticking goes over enough (for example 80ns then 80ns, meaning that the 1st loop increments tick and the second increases it by 2), then eventually there will be another loop that only has a 40ns delta, causing everything to even out.