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hashi

Gameloop and accuracy timer, feature/fix that was working, but not anymore

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I've implemented `Timer` class for high accuracy timing (for example for update logic/game-loop, sending ping each 15 seconds by WebRTC etc.)

setTimeout/setInterval fires once per second when tab is inactive, so how to gain accuracy timing?

We could set up `setTimeout/setInterval` in WebWorker, because in WebWorkers when tab is inactive, `setTimeout/setInterval` still fires with it's own interval/delay.

We could then send message `postmessage/onmessage` from WebWorker to Main Thread on each `setTimeout/setInterval` fire calls as a tick.

For some time this idea was working and was brilliant, but when I'm looking now (latest chrome version) this isn't working anymore because of `postmessage`, now `postmessage` delivers event with delay when tab is inactive..

Looks like Chrome Dev Team noticed this feautre, and they've fixed it.. but it wasn't a bug? gaah.. or maybe I have something wrong in the code:

https://jsfiddle.net/mfzmotb1/16/

    Timer = function Timer(callback, interval) {
        var id = Timer.prototype.__idCounter++;
    
        Timer.prototype.__hash[id] = callback;
    
        this.started = false;
    
        this.package = JSON.stringify({
            id: id,
            interval: interval
        });
    }
    
    Timer.prototype.__workerScript = function() {
        var __hash = {};
    
        onmessage = function(ev) {
            var data = JSON.parse(ev.data);
    
            if ( __hash[data.id] === undefined ) {
                __hash[data.id] = {
                    id: data.id,
                    lastTime: performance.now(),
                    interval: data.interval,
                    step: 0
                }
            }
            else delete __hash[data.id];
        }
    
        function loop(start) {
            if ( !start ) for ( var id in __hash ) step(__hash[id]);
    
            setTimeout(loop, 0);
        }
    
        loop(true);
    
        function step(unit) {
            while ( performance.now() - unit.lastTime >= unit.interval ) {
                unit.lastTime += unit.interval;
                unit.step++;
                var now = Date.now();
                console.log("ww", unit.step, "-", now/1000);
                postMessage(JSON.stringify({id: unit.id, time: now, step: unit.step}));
            }
        }
    }
    
    Timer.prototype.__idCounter = 0;
    Timer.prototype.__hash = {};
    
    Timer.prototype.__worker = new Worker(URL.createObjectURL(new Blob(['('+Timer.prototype.__workerScript.toString()+')()'], {type: 'application/javascript'})));
    
    Timer.prototype.__worker.onmessage = function(ev) {
        var data = JSON.parse(ev.data);
        Timer.prototype.__hash[data.id](data.time, data.step);
    }
    
    Timer.prototype.start = function(){
        if ( !this.started ) {
            Timer.prototype.__worker.postMessage(this.package);
            this.started = true;
        }
    }
    
    Timer.prototype.stop = function(){
        if ( this.started ) {
            Timer.prototype.__worker.postMessage(this.package);
            this.started = false;
        }
    }
    
    var timer = new Timer(function(wwTime, step) {
        var now = Date.now();
        console.log("m_", step, "-", wwTime/1000, now/1000, (now-wwTime)/1000);
    }, 100);
    
    console.log("starting in 2sec, so you have time to switch tabs");
    
    setTimeout(function() {
        timer.start();
    }, 2000);

Basically this code produce new class called `Timer`, there is WebWorker based on one function body `Timer.prototype.__workerScript` <- this fn's body happens in WebWorker.

One WebWorker handles all instances of Timer, each instance is for one timer.

Any ideas how to fix it? Here goes output:

Some tips:

    ww - console.log called from webworker
    m_ - console.log called from main thread
    
    1,2,3 - number of timer step

Tab Active:

    starting in 2sec
    ww 1 - 1485111848.697 //webworker tick time in seconds
    m_ 1 - 1485111848.697 1485111848.707 0.01 //webworker tick time, main thread tick time, diff
    ww 2 - 1485111848.798
    m_ 2 - 1485111848.798 1485111848.799 0.001
    ww 3 - 1485111848.898
    m_ 3 - 1485111848.898 1485111848.898 0
    ...

Tab Inactive:

    starting in 2sec
    ww 1 - 1485110821.95 //webworker tick time in seconds
    ww 2 - 1485110822.049
    ww 3 - 1485110822.149
    m_ 1 - 1485110821.95 1485110822.169 0.219 //webworker tick time, main thread tick time, diff
    m_ 2 - 1485110822.049 1485110822.17 0.121
    m_ 3 - 1485110822.149 1485110822.171 0.022
    ...

 

Do you know any ideas for measuring time for html5 gaming without throttle?

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