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Making a clock that takes 2560ms to complete a revolution in JavaScript

I'm trying to make a clock for a Libet task - a cognitive task used by psychologists. By convention these clocks take 2560 ms to complete a revolution. Mine seems to be running quite a lot slower and I can figure out why.
I have made an example of the issue here: https://jsfiddle.net/Sumoza/re4v7Lcj/8/
On each iteration of a setInterval with a 1ms delay, I increase the angle of rotation of the hand by (Math.PI*2)/2560, i.e. 1/2560th of a circle in radians. So, incrementing one of these each ms should complete the circle in that number of ms. As you can see from the clock, this runs a fair bit slower. Can anyone shed any light as to why. Interestingly, *10 seems to look a lot closer to what I want - but that doesn't make much sense to me so I'm wary of the fix. Relevant JS from the fiddle below. Thanks for any help.
var time = 0;
var rad_tick = (Math.PI*2)/2560; //radians per tick: last number is ms per revolution
// Draw Clock
const clock = document.getElementById('clock')
const clock_ctx = clock.getContext('2d')
clock_ctx.translate(clock.width/2, clock.height/2);
radius = (clock.height/2) * 0.7;
function drawClock() {
clock_ctx.clearRect(-clock.width/2, -clock.height/2, clock.width, clock.height);
clock.style.backgroundColor = 'transparent';
clock_ctx.beginPath();
clock_ctx.arc(0, 0, radius, 0 , 2 * Math.PI);
clock_ctx.stroke();
}
drawClock();
// Draw Hand
const hand = document.getElementById('hand')
const hand_ctx = hand.getContext('2d')
hand_ctx.translate(hand.width/2, hand.height/2);
function drawHand(time){
hand_ctx.clearRect(-hand.width/2, -hand.height/2, hand.width, hand.height);
hand_ctx.beginPath();
hand_ctx.moveTo(0,0);
hand_ctx.rotate(time);
hand_ctx.lineTo(0, -radius*0.9);
hand_ctx.stroke();
hand_ctx.rotate(-time);
}
function drawTime(){
time+=rad_tick;//*10
drawHand(time)
}
var intervalId = setInterval(drawTime, 1);

Try this
var starttime = new Date().getTime();
function drawTime() {
var elapsed = new Date().getTime() - starttime;
var time = elapsed % 2560;
time = time * rad_tick;
console.log(elapsed + "->" + time);
drawHand(time)
}

Base things on the current time, and don't depend on setInterval to fire at the exact time you set it to fire. If there are things in-queue at the time that setInterval is supposed to fire, it will do those things in-queue first and only then run the function you've wired to setIterval (causing the delays you see --which build up more and more over time). Learn about the event loop and requestAnimationFrame.
Instead, get the time (freshly) prior to doing something, and calculate how much time has passed since the start time. Base your animations on these calculations. This way, even if there are slight delays, your last action will always sync things to the way they're supposed to look right now.
When you do it this way, you might lose some frames (skipping things the engine didn't have time to do), but it will likely complete much closer to the expected completion time.
The bottom line is, if you tell the browser to do more than it can do in a particular amount of time, there will be delays. However, you can skip frames of an animation to make things complete much closer to the expected completion time.

You ask setInterval to call your callback every 1ms, but does it actually call it every 1ms?
Try this code:
let cnt = 0;
setInterval(() => cnt++, 1);
setTimeout(() => { console.log(cnt); }, 1000);
For me, it prints something between 230 and 235. So looks like the actual (average) minimum interval for me is a bit over 4ms.

Adding on to Stig, since javascript isn't super fast when it comes to these things, it won't be super accurate. Using something like getTime() will allow proper timing. How about you call getTime in your drawTime function, so that around every millisecond, it will check the actual time and use that value.

Why does millisecond counter keep going in requestAnimationFrame()?

I'm making a game in JavaScript, using the great requestAnimationFrame(callback) function.
Today I learned that the callback passed to requestAnimationFrame() gets a high resolution time measured since we opened that page. Let's call it ms:
function paint(ms) {
// draw my game
requestAnimationFrame(paint);
}
requestAnimationFrame(paint);
It's all great, but there's one thing I don't quite get.
Function requestAnimationFrame() doesn't do anything when we go to another tab, so the rendering is paused. On the other hand, the time passed to the callback still goes on when we leave. Because of this, I'm not sure how would I make any use of that value. If it worked proportionally with rendering engine, I could use ms to calculate logical time of my game, because relying on requestAnimationFrame() as a rock stable 60 FPS doesn't sound like the greatest idea.
Am I missing something? What's the purpose of the ms parameter if it continues to count when we leave our tab?

That's just a timestamp, it doesn't really count anything. It's indeed generally the same as performance.now() which gives the amount of time since the page is active. As to why, it's just how the DOMHighResTimeStamp's origin has been defined.
We usually use it as a way to know how long time has elapsed since some prior event occurred, that is we store a start_time, then check the current timestamp and we can get the delta time of our animation, regardless of the actual frame-rate.
By the way, no, relying on requestAnimationFrame to be at any fixed frame-rate is really not a good idea, requestAnimationFrame is not tied to any frame-rate by specs, and actually it is recommended to align it with the screen refresh-rate (though only Blink does so).
So you actually need to rely on such a timestamp in order to have a consistent speed across different setups. Doing a simple pos++ at every frame will make your animation run twice faster on a 120Hz monitor than on a 60Hz one (at least in Chrome).
This only makes your idea more complex to perceive how it could be implemented: would your paint-timer go twice faster when the window is moved to a 120Hz monitor?
This timestamp may also help to catch up on long frames, it's not because the system had a hiccup that you necessarily want your animation to last longer.
Similarly, not all cases want the animation logic to stop when the window is blurred. Let's say I have a header with a background animation powered by rAF, I don't really want it to pause when going off-screen, even though it didn't have been painted.
If you want your game logic to pause when the window is blurred, listen for the onvisibilitychange, and save the current timestamp (using performance.now() since we're outside of rAF).

To add to Kaiido's answer. It's also common in apps to limit the time delta. For example a common way framerate independant calculations in apps is to compute the time between frames
let previousTime = 0;
function loop(currentTime) {
const deltaTime = currenTime - previousTime;
previousTime = currentTime;
// use deltaTime in various calculations
posX = posX + velX * deltaTime;
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
But, sometimes collision and or other math can break if deltaTime is too large so games will often add a limiter
// don't let deltaTime be more than a 1/10 of a second
const deltaTime = Math.min(currenTime - previousTime, 1000 / 10);
This mostly removes the need for checking for onvisiblitiychange. Especially if you keep your own animation/game clock.
let previousTime = 0;
let clock = 0;
let clockRate = 1;
function loop(currentTime) {
const deltaTime = Math.min(currenTime - previousTime, 1000 / 10) * clockRate;
previousTime = currentTime;
clock += deltaTime; // update our own clock
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
Now not only will or clock not jump if the player hides the tab but we can set clockRate to 0 if we want things to pause.
Why use your own clock? It lets you easily slow down or speed up time for all calculations that depend on that clock (see clockRate above). Also many app (games) have multiple clocks. They'd compute a different deltaTime for each clock. For example one clock for all objects that need to pause vs clocks need to keep going even even with the app/game is pause. Another might be a clock for the player vs one for the enemies so that when the player uses their "slow time super power" the enemies motions go slow but the player's motions remain at the same speed.

HTML/Javascript Ascending Number

I'm trying to make a simple javascript game. Basically, you get pancakes at a certain amount per second. In the code, I call this value (the rate at which you get pancakes) pps. I want to make it so that as the HTML span tag that shows the total amount of pancakes gets more pancakes, (at the rate of pps), it ascends so it looks nicer.
For example, if I get pancakes at 5 pps, right now it just goes 0, 5, 10, etc... every second. I want it to go 0,1,2,3,4,5(1 second), next second 6,7,8,9,10, etc...
Here is the code that I have so far, for the pancake counter:
pps = 100;
tp = 0;
window.setInterval(function(){
tp += parseInt(pps);
document.getElementById("test").innerHTML = tp;
}, 1000);
Anyone know how to do this?

This is a problem common to all games, and one that you need to solve correctly for your game to work outside of your own computer.
The correct solution is that you need to measure the elasped time between each iteration of your game loop, or between each frame render. This is, in practice, going to be a very small number; you can think of this number as a "scaling factor".
If your game was about moving a space ship, and you wanted it to move 5 screen units per second, your game loop would:
Find the time elapsed since the last interval, in seconds. In a game rate-limited to 60 frames-per-second, this would be around 1/60th of a second
Multiply the ship's speed (5 units per second) by 1/60; the ship would move 0.8333... units this tick
move the ship by that amount.
By the time 1 full second has passed, the ship will have moved 5 units.
The exact same principal applies to your PPS.
The important part is that, in the real world, it will not be exactly 1/60th of a second between frames. If you're not computing the "scaling factor" each iteration of your loop, your game will slowly accrue error. setInterval is particularly bad for this, and not at all suitable as a source for time in a game.
The implementation in JavaScript is simple: Each game loop, record the current time from whatever source of time is available to you; in your case, you can use get Date().getTime(), which returns the time since the UNIX epoch in milliseconds. Record this value.
In the subsequent redraw, you will again call get Date().getTime(), and then subtract the previous value to the the elapsed time. That is your scaling factor, in milliseconds. You can multiply pps by that value to determine how many pancakes to add.
It's important that you still follow this approach, even if you're using setInterval. You might think you can simply setInterval(..., 1000 / 60) to invoke your callback 60 times per second, but setInterval (and setTimeout) are not accurate - they invoke your callback at least that far in the future, but potentially much further. You still need to scale pps by the elapsed times since the last redraw.
Here's a simple implementation:
var PPS = 5;
var lastTime = new Date().getTime();
var cakes = 0;
setInterval(function () {
var currentTime = new Date().getTime()
var elapsedTime = currentTime - lastTime;
lastTime = currentTime;
cakes += (PPS * (elapsedTime / 1000)) // elapsedTime is in milliseconds, divide by 1000 to get fractional seconds
document.getElementById('pps').innerText = cakes;
}, 10);
<div id="pps"></div>
As an aside, the incorrect solution is one you find in a lot of old games: Increment things as fast as you can. On old computers this was a viable solution; the game redrew slowly enough that the game would advance smoothly. As computers got faster, the game would run faster, until it became unplayable.

A simple interval timer would do the trick. Something like this:
function incrementToNumber(tag, currentNumber, targetNumber) {
var numTicks = targetNumber - currentNumber;
var interval = setInterval(function() {
currentNumber++;
tag.innerText = currentNumber;
if(currentNumber == targetNumber) {
clearInterval(interval);
}
}, 1000 / numTicks);
}
That particular function increments over the course of one second. To change the time it takes to increment, swap out the 1000 with whatever milliseconds you want it to take.
For a version that increases forever:
function inrementForever(tag, currentPancakes, pancakesPerSecond) {
setInterval(function() {
currentPancakes++;
tag.innerText = currentPancakes;
}, 1000 / pancakesPerSecond);
}

get a smooth animation for a canvas game

How to get a better animation, dinamically, even when browser is busy or idle, for different devices which have different hardware capacity.
I have tried many ways and still cannot find the right way to make the game to display a better animation.
This is what i tried:
var now;
var then = Date.now();
var delta;
window.gamedraw = function(){
now = Date.now();
delta = now - then;
if(delta > 18){
then = now - (delta % 18);
game_update();
}
}
window.gameloop = setInterval(window.gamedraw,1);
18 is the interval value to update the game, but when browser is busy this interval is not good, and it needs to lower. How to get a better animation dinamically, even when browser is idle or busy ?
I suppose that the interval value is the problem, because if interval is lower then game animation is very fast, if this value is 18 then game animation is good but not when browser is busy, and I do not have idea how to change it dinamically.

To get a smooth animation, you must :
• Synchronise on the screen.
• Compute the time elapsed within your game.
• Animate only using this game time.
Synchronizing with the screen is done by using requestAnimationFrame (rAF).
When you write :
requestAnimationFrame( myCalbBack ) ;
You are registering myCalbBack to be called once, the next time the screen is available to draw on.
( If you know about double buffering (canvas are always double-buffered), this time is the next time the GPU will swap the draw buffer with the display buffer. )
If, on the other hand, you don't use rAF but a interval/timeout to schedule the draws, what will happen is that the draws won't get actually displayed until next display refresh. Which might happen (on a 60Hz display) any time from right now to 16.6 ms later.
Below with a 20ms interval and a 16 ms screen, you can see that the images actually displayed will be alternatively 16ms away OR 2*16ms away - never 20, for sure-. You just can't know, from the interval callback, when the actual draw will show. Since both rAF and Intervals are not 100% accurate, you can even have a 3 frames delta.
So now that you are on sync with the screen, here's a bad news : the requestAnimationFrame does not tick exactly regularly. For various reasons the elapsed time in between two frames might change of 1ms or 2, or even more. So if you are using a fixed movement each frame, you'll move by the same distance during a different time : the speed is always changing.
(expl : +10 px on each rAF,
16.6 display -->> rAF time of 14, 15, 16 or 17 ms
--> the apparent speed varies from 0.58 to 0.71 px/ms. )
Answer is to measure time... And use it !
Hopefully requestAnimationFrame provides you the current time so you don't even have to use Date.now(). Secondary benefit is that this time will be very accurate on Browsers having an accurate timer (Chrome desktop).
The code below shows how you could know the time elapsed since last frame, and compute an application time :
function animate(time) {
// register to be called again on next frame.
requestAnimationFrame(animate);
// compute time elapsed since last frame.
var dt = time-lastTime;
if (dt<10) return;
if (dt >100) dt=16; // consider only 1 frame elapsed if unfocused.
lastTime=time;
applicationTime+=dt;
//
update(dt);
draw();
}
var lastTime = 0;
var applicationTime = 0;
requestAnimationFrame(animate);
Now last step is to always use time inside all you formulas. So instead of doing
x += xSpeed ;
you'll have to do :
x += dt * xSpeed ;
And now not only the small variations in between frames will be taken into account, but your game will run at the same apparent speed whatever the device's screen (20Hz, 50Hz, 60 Hz, ...).
I did a small demo where you can choose both the sync and if using fixed time, you'll be able to judge of the differences :
http://jsbin.com/wesaremune/1/

You should use requestAnimationFrame instead of setInterval.
Read this article or this one.
The latter one is in fact exactly discussing your approach (with the delta time), and then introduces the animation frame as a more reliable alternative.
The first article is really a great resource. For starters, with your interval of 18 ms you're apparently aiming for something close to 60 fps. This is in fact the default for requestAnimationFrame, so you don't need to write anything special:
function gamedraw() {
requestAnimationFrame(gamedraw); //self-reference
game_update(); //your update logic, propably needs to handle time intervals internally
}
gamedraw(); //this starts the animation
If you want to set the update interval explicitly, you can do so by wrapping the requestAnimationFrame inside a setInterval, like this:
var interval = 18;
function gamedraw() {
setTimeout(function() {
requestAnimationFrame(gamedraw);
game_update(); //must handle time difference internally
}, interval);
}
gamedraw();
Note that the game_update() function must keep track of when it was last called in order to e.g. move everything twice as far as normal in case a frame had to be skipped.
Actually, this means you could (and probably should) refactor your game_update() function to take the time that has actually passed as an argument instead of determining that internally. (There's no functional difference, it just is better, clearer code IMO because it doesn't hide the timing magic.)
var time;
function gamedraw() {
requestAnimationFrame(gamedraw);
var now = new Date().getTime(),
dt = now - (time || now);
time = now; //reset the timer
game_update(dt); //update with explicit and variable time step
}
gamedraw();
(Here I dropped the explicit frames again.)
Still, I urge you to read the first article because it also deals with cross-browser issues that I haven't gotten into here.

You should use requestAnimationFrame. It will queue up a callback to run on the next time the browser renders a frame. To achieve constant updating, call the update function recursively.
var update = function(){
//Do stuff
requestAnimationFrame(update)
}

HTML5 Canvas game loop delta time calculations

I'm new to game development. Currently I'm doing a game for js13kgames contest, so the game should be small and that's why I don't use any of modern popular frameworks.
While developing my infinite game loop I found several articles and pieces of advice to implement it. Right now it looks like this:
self.gameLoop = function () {
self.dt = 0;
var now;
var lastTime = timestamp();
var fpsmeter = new FPSMeter({decimals: 0, graph: true, theme: 'dark', left: '5px'});
function frame () {
fpsmeter.tickStart();
now = window.performance.now();
// first variant - delta is increasing..
self.dt = self.dt + Math.min(1, (now-lastTime)/1000);
// second variant - delta is stable..
self.dt = (now - lastTime)/16;
self.dt = (self.dt > 10) ? 10 : self.dt;
self.clearRect();
self.createWeapons();
self.createTargets();
self.update('weapons');
self.render('weapons');
self.update('targets');
self.render('targets');
self.ticks++;
lastTime = now;
fpsmeter.tick();
requestAnimationFrame(frame);
}
requestAnimationFrame(frame);
};
So the problem is in self.dt I've eventually found out that first variant is not suitable for my game because it increases forever and the speed of weapons is increasing with it as well (e.g. this.position.x += (Math.cos(this.angle) * this.speed) * self.dt;..
Second variant looks more suitable, but does it correspond to this kind of loop (http://codeincomplete.com/posts/2013/12/4/javascript_game_foundations_the_game_loop/)?

Here' an implementation of an HTML5 rendering system using a fixed time step with a variable rendering time:
http://jsbin.com/ditad/10/edit?js,output
It's based on this article:
http://gameprogrammingpatterns.com/game-loop.html
Here is the game loop:
//Set the frame rate
var fps = 60,
//Get the start time
start = Date.now(),
//Set the frame duration in milliseconds
frameDuration = 1000 / fps,
//Initialize the lag offset
lag = 0;
//Start the game loop
gameLoop();
function gameLoop() {
requestAnimationFrame(gameLoop, canvas);
//Calcuate the time that has elapsed since the last frame
var current = Date.now(),
elapsed = current - start;
start = current;
//Add the elapsed time to the lag counter
lag += elapsed;
//Update the frame if the lag counter is greater than or
//equal to the frame duration
while (lag >= frameDuration){
//Update the logic
update();
//Reduce the lag counter by the frame duration
lag -= frameDuration;
}
//Calculate the lag offset and use it to render the sprites
var lagOffset = lag / frameDuration;
render(lagOffset);
}
The render function calls a render method on each sprite, with a reference to the lagOffset
function render(lagOffset) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
sprites.forEach(function(sprite){
ctx.save();
//Call the sprite's `render` method and feed it the
//canvas context and lagOffset
sprite.render(ctx, lagOffset);
ctx.restore();
});
}
Here's the sprite's render method that uses the lag offset to interpolate the sprite's render position on the canvas.
o.render = function(ctx, lagOffset) {
//Use the `lagOffset` and previous x/y positions to
//calculate the render positions
o.renderX = (o.x - o.oldX) * lagOffset + o.oldX;
o.renderY = (o.y - o.oldY) * lagOffset + o.oldY;
//Render the sprite
ctx.strokeStyle = o.strokeStyle;
ctx.lineWidth = o.lineWidth;
ctx.fillStyle = o.fillStyle;
ctx.translate(
o.renderX + (o.width / 2),
o.renderY + (o.height / 2)
);
ctx.beginPath();
ctx.rect(-o.width / 2, -o.height / 2, o.width, o.height);
ctx.stroke();
ctx.fill();
//Capture the sprite's current positions to use as
//the previous position on the next frame
o.oldX = o.x;
o.oldY = o.y;
};
The important part is this bit of code that uses the lagOffset and the difference in the sprite's rendered position between frames to figure out its new current canvas position:
o.renderX = (o.x - o.oldX) * lagOffset + o.oldX;
o.renderY = (o.y - o.oldY) * lagOffset + o.oldY;
Notice that the oldX and oldY values are being re-calculated each frame at the end of the method, so that they can be used in the next frame to help figure out the difference.
o.oldX = o.x;
o.oldY = o.y;
I'm actually not sure if this interpolation is completely correct or if this is best way to do it. If anyone out there reading this knows that it's wrong, please let us know :)

The modern version of requestAnimationFrame now sends in a timestamp that you can use to calculate elapsed time. When your desired time interval has elapsed you can do your update, create and render tasks.
Here's example code:
var lastTime;
var requiredElapsed = 1000 / 10; // desired interval is 10fps
requestAnimationFrame(loop);
function loop(now) {
requestAnimationFrame(loop);
if (!lastTime) { lastTime = now; }
var elapsed = now - lastTime;
if (elapsed > requiredElapsed) {
// do stuff
lastTime = now;
}
}

This isn't really an answer to your question, and without knowing more about the particular game I can't say for sure if it will help you, but do you really need to know dt (and FPS)?
In my limited forays into JS game development I've found that often you don't really need to to calculate any kind of dt as you can usually come up with a sensible default value based on your expected frame rate, and make anything time-based (such as weapon reloading) simply work based on the number of ticks (i.e. a bow might take 60 ticks to reload (~1 second # ~60FPS)).
I usually use window.setTimeout() rather than window.requestAnimationFrame(), which I've found generally provides a more stable frame rate which will allow you to define a sensible default to use in place of dt. On the down-side the game will be more of a resource hog and less performant on slower machines (or if the user has a lot of other things running), but depending on your use case those may not be real concerns.
Now this is purely anecdotal advice so you should take it with a pinch of salt, but it has served me pretty well in the past. It all depends on whether you mind the game running more slowly on older/less powerful machines, and how efficient your game loop is. If it's something simple that doesn't need to display real times you might be able to do away with dt completely.

At some point you will want to think about decoupling your physics from your rendering. Otherwise your players could have inconsistent physics. For example, someone with a beefy machine getting 300fps will have very sped up physics compared to someone chugging along at 30fps. This could manifest in the first player cruising around in a mario-like scrolling game at super speed and the other player crawling at half speed (if you did all your testing at 60fps). A way to fix that is to introduce delta time steps. The idea is that you find the time between each frame and use that as part of your physics calculations. It keeps the gameplay consistent regardless of frame rate. Here is a good article to get you started: http://gafferongames.com/game-physics/fix-your-timestep/
requestAnimationFrame will not fix this inconsistency, but it is still a good thing to use sometimes as it has battery saving advantages. Here is a source for more info http://www.chandlerprall.com/2012/06/requestanimationframe-is-not-your-logics-friend/

I did not check the logic of the math in your code .. however here what works for me:
GameBox = function()
{
this.lastFrameTime = Date.now();
this.currentFrameTime = Date.now();
this.timeElapsed = 0;
this.updateInterval = 2000; //in ms
}
GameBox.prototype.gameLoop = function()
{
window.requestAnimationFrame(this.gameLoop.bind(this));
this.lastFrameTime = this.currentFrameTime;
this.currentFrameTime = Date.now();
this.timeElapsed += this.currentFrameTime - this.lastFrameTime ;
if(this.timeElapsed >= this.updateInterval)
{
this.timeElapsed = 0;
this.update(); //modify data which is used to render
}
this.render();
}
This implementation is idenpendant from the CPU-speed(ticks). Hope you can make use of it!

A great solution to your game engine would be to think in objects and entities. You can think of everything in your world as objects and entities. Then you want to make a game object manager that will have a list of all your game objects. Then you want to make a common communication method in the engine so game objects can make event triggers. The entities in your game for example a player would not need to inherent from anything to get the ability to render to the screen or have collision detection. You would simple make common methods in the entity that the game engine is looking for. Then let the game engine handle the entity as it would like. Entities in your game can be created or destroyed at anytime in the game so you should not hard-code any entities at all in the game loop.
You will want other objects in your game engine to respond to event triggers that the engine has received. This can be done using methods in the entity that the game engine will check to see if the method is available and if it is would pass the events to the entity. Do not hard code any of your game logic into the engine it messes up portability and limits your ability to expand on the game later on.
The problem with your code is first your calling different objects render and updates not in the correct order. You need to call ALL your updates then call ALL your renders in that order. Another is your method of hard coding objects into the loop is going to give you a lot of problems, when you want one of the objects to no longer be in the game or if you want to add more objects into the game later on.
Your game objects will have an update() and a render() your game engine will look for that function in the object/entity and call it every frame. You can get very fancy and make the engine work in a way to check if the game object/entity has the functions prior to calling them. for example maybe you want an object that has an update() but never renders anything to the screen. You could make the game object functions optional by making the engine check prior to calling them. Its also good practice to have an init() function for all game objects. When the game engine starts up the scene and creates the objects it will start by calling the game objects init() when first creating the object then every frame calling update() that way you can have a function that you only run one time on creation and another that runs every frame.
delta time is not really needed as window.requestAnimationFrame(frame); will give you ~60fps. So if you're keeping track of the frame count you can tell how much time has passed. Different objects in your game can then, (based off of a set point in the game and what the frame count was) determine how long its been doing something based off its new frame count.
window.requestAnimationFrame = window.requestAnimationFrame || function(callback){window.setTimeout(callback,16)};
gameEngine = function () {
this.frameCount=0;
self=this;
this.update = function(){
//loop over your objects and run each objects update function
}
this.render = function(){
//loop over your objects and run each objects render function
}
this.frame = function() {
self.update();
self.render();
self.frameCount++;
window.requestAnimationFrame(frame);
}
this.frame();
};
I have created a full game engine located at https://github.com/Patrick-W-McMahon/Jinx-Engine/ if you review the code at https://github.com/Patrick-W-McMahon/Jinx-Engine/blob/master/JinxEngine.js you will see a fully functional game engine built 100% in javascript. It includes event handlers and permits action calls between objects that are passed into the engine using the event call stack. check out some of the examples https://github.com/Patrick-W-McMahon/Jinx-Engine/tree/master/examples where you will see how it works. The engine can run around 100,000 objects all being rendered and executed per frame at a rate of 60fps. This was tested on a core i5. different hardware may vary. mouse and keyboard events are built into the engine. objects passed into the engine just need to listen for the event passed by the engine. Scene management and multi scene support is currently being built in for more complex games. The engine also supports high pixel density screens.
Reviewing my source code should get you on the track for building a more fully functional game engine.
I would also like to point out that you should have requestAnimationFrame() called when you're ready to repaint and not prior (aka at the end of the game loop). One good example why you should not call requestAnimationFrame() at the beginning of the loop is if you're using a canvas buffer. If you call requestAnimationFrame() at the beginning, then begin to draw to the canvas buffer you can end up having it draw half of the new frame with the other half being the old frame. This will happen on every frame depending on the time it takes to finish the buffer in relation to the repaint cycle (60fps). But at the same time you would end up overlapping each frame so the buffer will get more messed up as it loops over its self. This is why you should only call requestAnimationFrame() when the buffer is fully ready to draw to the canvas. by having the requestAnimationFrame() at the end you can have it skip a repaint if the buffer is not ready to draw and so every repaint is drawn as it is expected. The position of requestAnimationFrame() in the game loop has a big difference.