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Is there a simple way to make a game loop in JavaScript? something like...
onTimerTick() { // update game state } 
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There are a varied amount of ways to achieve this using JavaScript depending on your application. A setInterval() or even with a while() statement would do the trick. This will not work for a game loop. JavaScript interpreted by the browser, so it is prone to interrupts. Interrupts will make the play back of your game feel jittery.
The webkitRequestAnimationFrame properties of CSS3 aims to correct this by managing the rendering loop itself. However this is still not the most efficient way to do this and will be prone to jitters if you have alot of objects being updated.
This is a good website to get started with:
http://nokarma.org/2011/02/02/javascript-game-development-the-game-loop/index.html
This site has some good information on the basics of making a game loop. It does not touch upon any sort of object oriented design by any means. The most accurate way to achieve precise timings is by using the date function.
while ((new Date).getTime() > nextGameTick && loops < maxFrameSkip) { Game.update(); nextGameTick += skipTicks; loops++; } This does not take into account how setTimeout drifts at high frequencies. This will also lead to things getting out of sync and becoming jittery. JavaScript will drift +/- 18ms per second.
var start, tick = 0; var f = function() { if (!start) start = new Date().getTime(); var now = new Date().getTime(); if (now < start + tick*1000) { setTimeout(f, 0); } else { tick++; var diff = now - start; var drift = diff % 1000; $('<li>').text(drift + "ms").appendTo('#results'); setTimeout(f, 990); } }; setTimeout(f, 990); Now lets put all of this into a working example. We want to inject our game loop into WebKit’s managed rendering loop. This will help smooth out the rendered graphics. We also want to split up the draw and update functions. This will update the objects in our rendering scene before calculating when the next frame should be drawn. The game loop should also skip draw frames if updating takes to long.
Index.html
<html> <head> <!--load scripts--> </head> <!-- render canvas into body, alternative you can use div, but disable right click and hide cursor on parent div --> <body oncontextmenu="return false" style="overflow:hidden;cursor:none;-webkit-user-select: none;-moz-user-select: none;-ms-user-select: none;user-select: none;"> <script type="text/javascript" charset="utf-8"> Game.initialize(); window.onEachFrame(Game.run); </script> </body> </html> Game.js
var Game = {}; Game.fps = 60; Game.maxFrameSkip = 10; Game.skipTicks = 1000 / Game.fps; Game.initialize = function() { this.entities = []; this.viewport = document.body; this.input = new Input(); this.debug = new Debug(); this.debug.initialize(this.viewport); this.screen = new Screen(); this.screen.initialize(this.viewport); this.screen.setWorld(new World()); }; Game.update = function(tick) { Game.tick = tick; this.input.update(); this.debug.update(); this.screen.update(); }; Game.draw = function() { this.debug.draw(); this.screen.clear(); this.screen.draw(); }; Game.pause = function() { this.paused = (this.paused) ? false : true; }; /* * Runs the actual loop inside browser */ Game.run = (function() { var loops = 0; var nextGameTick = (new Date).getTime(); var startTime = (new Date).getTime(); return function() { loops = 0; while (!Game.paused && (new Date).getTime() > nextGameTick && loops < Game.maxFrameSkip) { Game.update(nextGameTick - startTime); nextGameTick += Game.skipTicks; loops++; } Game.draw(); }; })(); (function() { var onEachFrame; if (window.requestAnimationFrame) { onEachFrame = function(cb) { var _cb = function() { cb(); requestAnimationFrame(_cb); }; _cb(); }; } else if (window.webkitRequestAnimationFrame) { onEachFrame = function(cb) { var _cb = function() { cb(); webkitRequestAnimationFrame(_cb); }; _cb(); }; } else if (window.mozRequestAnimationFrame) { onEachFrame = function(cb) { var _cb = function() { cb(); mozRequestAnimationFrame(_cb); }; _cb(); }; } else { onEachFrame = function(cb) { setInterval(cb, Game.skipTicks); }; } window.onEachFrame = onEachFrame; })(); Even More Information
You can find a full working example, and all of the code here. I have convert this answer into a downloadable javascript framework you can build your games off from.
https://code.google.com/p/twod-js/
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setInterval(onTimerTick, 33); // 33 milliseconds = ~ 30 frames per sec function onTimerTick() { // Do stuff. } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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