Currently, I am rendering WebGL content using requestAnimationFrame which runs at (ideally) 60 FPS. I'm also concurrently scheduling an "update" process, which handles AI, physics, and so on using setTimeout. I use the latter because I only really need to update objects roughly 30 times per second, and it's not really part of the draw sequence; it seemed like a good idea to save the remaining CPU for actual render passes, since most of my animations are fairly hardware intensive.
My question is one of best practices. setTimeout and setInterval are not particularly kind to battery life and CPU consumption, especially when the browser is not in focus. On the other hand, using requestAnimationFrame (or tying the updates directly into the existing render phase) will potentially enforce far more updates every second than are strictly necessary, and may stop updating altogether when the browser is not in focus or at other times the browser deems unnecessary for "animation".
What is the best course of action for updating, but not rendering content?
setTimeout and setInterval are not particularly kind to battery life and CPU consumption
Let's be honest: Neither is requestAnimationFrame. The difference is that RAF automatically turns off when you leave the tab. That behavior can be emulated with setTimeout if you use the Page Visibility API, though, so in reality the power consumption problems between the two are about on par if used intelligently.
Beyond that, though, setTimeout\Interval is perfectly appropriate for use in your case. The only thing that you may want to be aware of is that you'll be hard pressed to get it perfectly in sync with the render loop. You'll have cases where you may draw one too many times before your animation update hits, which can lead to minor stuttering. If you're rendering at 60hz and updating at 30hz it shouldn't be a big issue, but you'll want to be aware of it.
If staying perfectly in sync with the render loop is important to you, you could simply have a if(framecount % 2) { updateLogic(); } at the top of your RAF callback, which effectively limits your updates to 30hz (every other frame) and it's always in sync with the draw.
Related
We're building a web framework and have identified forced reflows as one of the main performance bottlenecks of our applications. From web research, we learned that actions that trigger forced reflows should be grouped into read- and write-batches to minimize the number of reads that actually are costly (because something changed). [Our main goal is to get rid of forced reflows altogether, but we doubt that we can remove every single one – and from what we learned it is the first one after a change that is expensive.]
In a proof of concept, we implemented this batch approach using the fastdom library for a single application start. Surprisingly, instead of the performance increase, we hoped for, the startup performance decreased from (in median) 372ms to 391ms time to interactive. In the performance trace, we see that the large recalculate style/layout cycle now directly comes from revealing the changed HTML, and that the js-triggered forced reflows (in the animation frame after that reveal) are actually fast. However, the overall performance was better with the forced reflows happening before the reveal.
performance trace before implementing fastdom:
performance trace after implementing fastdom:
Can someone explain why we observe this behavior? Why does it seem that the community-approved approach works in the opposite direction in our case?
Thanks for all hints in advance!
How can I control the rendering loop frame rate in KineticJS? The docs for Kinetic.Animation show a frame rate being passed to the render callback, and Kinetic.Tween seems to have no frame rate logic, but I don't see anyway to force, say, a 30fps when 60fps is possible.
Loads of context for the curious follows, but the question is that simple. If anyone reads on, other advice is welcome. If you already know the answer, don't waste your time reading on!
I'm developing a music app that combines some DOM-based GUI controls (current iteration using jQuery Mobile) and Canvas-based GUI controls (using KineticJS). The latter involve some animation. Because the animated elements are triggered by music playback, I'm using Kinetic.Tween to avoid the complexity of remembering how long a given note has been playing (which Kinetic.Animation would require doing).
This approach works great at 60fps in Chrome (on a fast machine) but is just slow enough on iOS 6.1 Safari (iPad 2) that manipulating controls while animations are happening gets a little janky. I'm not using WebGL (unless KineticJS or Chrome does this by default for canvas?), and that's not an option when I package for native UIWebView.
As I'm getting beyond prototype into wanting to make more committed tech decisions, I see the following options, in order of perceived goodness:
Figure out how to cap the frame rate. Because my animations heavily use alpha fades but do not involve motion, I believe I could get away with 20-30fps and look fine. Could also scale this up on faster devices.
Don't respond immediately to touch inputs, but add them to a queue which I poll at a constant interval and only use the freshest for things like touchmove. This has no impact on my non-interactive animated elements, but tackles the problem from the other direction, trying to reduce the load of user interaction. This would require making Kinetic controls static and manually tracking touch coordinates (not terrible effort if it actually helped).
Rewrite DOM-based GUI to canvas-based (KineticJS); rewrite WebAudio-based engine to HTML5 audio; leverage CocoonJS or Ejecta for GPU-acceleration. This means having to hand-code stuff like file choosers and nav menus and such (bad). Losing WebAudio is pretty serious as it eliminates features like DSP effects and very fine-grained, low-latency timing (which is working just fine on an iPad 2).
Rewrite the app to separate DOM based GUI and WebAudio from Canvas-based elements, leverage CocoonJS. I'm not sure if/how well this works out, but the fact that CocoonJS passes JavaScript code as strings between the 2 components makes me very skittish about how solid this idea is. It's probably doable, but best case I'm very tied to CocoonJS moving forwards. I don't like architecting this way, but maybe it's not as bad as it sounds?
Make animations less juicy. This is least good not because of its design impact but because, as it is, I'm only animating ~20 simple shapes at any time in my central view component, however they include transparency and span an area ~1000x300. Other components like sliders are similarly bare-bones. In other words, it's not very juicy right now.
Overcome severe allergy to Objective-C; forget about the browser, Android, and that other mobile OS. Have a fast app that performs natively and has shiny Apple-approved widgets. My biggest problem with this approach is not wanting to be stuck in Objective-C reality for years, skillset-wise. I just don't like it.
Buy an iPad 3 or later. Since I already am pretending Android doesn't exist (I don't have any devices to test), why not pretend no one still has iPad 2? I think this is passing the buck -- if I can get acceptable performance on iPad 2, I will feel confident about the app's performance as I add more features.
I may be overlooking options or otherwise naive about how to tackle this. Some would say what I'm trying to build is just silly. But it's working pretty well just not ready for prime time on the iPad 2.
Yes, you can control the Kinetic.Animation framerate
The Kinetic.Animation sends in a frame object which has a frame.time property.
That .time is a running timer that you can use to throttle your animation speed.
Here's an example that throttles the Kinetic.Animation: http://jsfiddle.net/m1erickson/Hn3cC/
var lastTime;
var frameDelay=1000;
var loop = new Kinetic.Animation(function(frame) {
var time = frame.time
if(!lastTime){lastTime=time;}
var elapsed = time-lastTime;
if(elapsed>=frameDelay){
// frameDelay has expired, so animate stuff now
// set lastTime for the next loop
lastTime=time;
}
}, layer);
loop.start();
Working from #markE's suggestions, I tried a few things and found a solution. It's ultimately not rocket science, but sharing what I figured out:
First, tried the hack of doubling Tween durations and targets, using a timer to stop them at 50%. This kinda sorta worked but was hard to get to look good and was pretty error prone in coding bogus targets like negative opacity or height or whatnot.
Second, having read the source to Tween and looked at docs again for Animation, decided I could locally use Animation instances instead of Tween instances, and allow the closure scope to hang onto the relevant note properties. Eventually got this working smoothly and finally realized a big Duh! which is that throttling the frame rate of several independently animating things does not in any way throttle the overall frame rate.
Lastly, decided to give my component a render() method that calls itself in a loop with requestAnimationFrame, exits immediately if called before my clamp time, and inside render() I update all objects in the Kinetic canvas and call layer.drawScene(). Because there is now only one animation, this drops frame rate to whatever I need and the app is fast on iPad 2 (looks exactly the same to my eyes too).
So Kinetic is still helping for its higher level canvas API, and so far my other control widgets are still easy code using Kinetic to handle user input and dragging, now performing much better as the big beast component is not eating up the CPU.
The short answer to my original question is that no, you can't lock the overall frame rate for very complex animations, but as Mark said, you can for anything that fits in a single Animation instance.
Note that I could have still used Animation without giving it a layer or explicitly calling any draw() methods, but since I'd still have to write all the logic to determine individual element's current visual state, there was no gain to doing this. What would be very useful would be if Tween could accept a parameter to not automatically render. This would simplify code like mine, as I could shorthand the animation on individual objects but still choose when to actually do the heavy lifting of rendering everything. Seeing how much this whole exercise gained in performance on the iPad 2, might be worth adding this option to the framework.
I'm working on a multiple projectile simulator for a college project and I'm wondering how to best setup timing in JavaScript rendering to a HTML5 canvas
I'm using an Euler integrator setup for physics and accuracy is very important for this project. The rendering is very bare bones
My question is how to best setup the timing for all this.
Right now I have:
The physics and other logic running in a function that loops using setTimeout() with a fixed time step
The rendering in another function that loops using a requestAnimationFrame() call (flexible time step)
These two loops run sort of simultaneously (I know JavaScript doesn't really support threads without Web Workers) but I don't want the rendering (currently running at a much higher FPS than needed) to be unnecessarily 'stealing' CPU cycles from the physics simulation, if you see what I mean.
Given that physics accuracy is most important here how would you recommend setting up the timing system? (Maybe using Web Workers would be useful here but I havent seen this used in other engines)
Thanks!
I'd suggest that you don't try to 'multithread' unless you're actually doing it, and even then, I wouldn't necessarily recommend it.
The best way to keep everything in synch is to have a single thread of execution. A single setTimeout loop of about 33ms seems to work ok for my games.
Also, in my experience at least, setTimeout offers a much more aesthetic experience than setInterval or requestAnimationFrame. With setInterval, Javascript tries to hard to 'catch up' when frames are delivered late, which makes animation frames inconsistent. With requestAnimationFrame, frames are skipped to ensure a smooth running game, which actually makes things harder, because your users aren't entirely sure their view is up to date at any given second.
One way would be to set an interval for processing physics, and once per x frames, render everything.
var physicsTime;
var renderFrequency;
var frameCount;
setInterval(function(){updateStuff()},physicsTime);
then in updateStuff()
function updateStuff(){
frameCount ++;
if (frameCount >= renderFrequency){
frameCount -= renderFrequency;
render();
}
physics();
}
In my game engine, there are objects that need to be updated periodically. For example, a scene can be lowering its alpha, so I set an interval that does it. Also, the camera sometimes needs to jiggle a bit, which requires interpolation on the rotation property.
I see that there are two ways of dealing with these problems:
Have an update() method that calls all other object's update methods. The objects track time since they were last updated and act accordingly.
Do a setInterval for each object's update method.
What is the best solution, and why?
setInterval does not keep to a clock, it just sequences events as they come in. Browsers tend to keep at least some minor amount of time between events. So if you have 10 events that all need to fire after 100ms you'll likely see the last event fire well into the 200ms. (This is easy enough to test).
Having only one event (and calling update on all objects) is in this sense better than having each object set it's own interval. There may be other considerations though but for at least this reason option 2 is unfeasible.
Here is some more about setInterval How do browsers determine what time setInterval should use?
The best way I have found out to make a good update() function and keeping a good framerate and less load is as following.
Have a single update() method which draws your frame, by looping some sort of queue/schedule of all drawable object his own update() function which are added to this update event queue/ schedule. (eventlistener)
This way you don't have to loop all objects which are not scheduled for a redraw/update (like menu buttons or crosshairs). And you don't have an over abundance of intervals running for all drawable objects.
I recommend using the update() method over the setInterval.
Also, I would guess that the timing on the several setintervals running would be unreliable.
Another possibility, depending on what other things are happening in your game, using a bunch of separate intervals could introduce race conditions in the counting and comparing of scoring, etc
The proposed algorithms proposed are not exclusive to the related method. That is, you can use setInteval to call all the update methods, or you can have each object update itself by repeatedly calling setTimeout.
More to the point is that a single timer is less overhead than multiple timers (of either type). This really matters when you have lots of timers. On the other hand, only one timer may not suit because some objects might need to be updated more frequently than others, or to a different schedule, so just try to minimise them.
An advantage with setTimeout is that the interval to the next call can be adjusted to meet specific scheduling requirements, e.g. if one is delayed you can skip the next one or make it sooner. setInterval will slowly drift relative to a consistent clock and one–of adjustments are more difficult.
On the other hand, setInteval only needs to be called once so you don't have to keep calling the timer. You may end up with a combination.
I have a tree that gets populated through the web service - this part is super fast, the part that's a bit slower is populating the tree...I have a gif rotating image that rotates while the service is loading. Since I use ajaxStop and ajaxStart trigger, the gif stops rotating after ajax request has completed, which is correct. However, because the loading takes a split second, the gif freezes for that split second which looks unprofessional.
How do I make the gif rotate until the tree is finished loading?
Browsers give a low priority to image refreshing, so in the time your code is manipulating/inserting in the DOM, the browser is busy with that and doesn't have time to repaint the image.
There's not a whole lot you can do, besides optimizing your code so that the processing you're doing with the ajax data is less intensive, or for example if you're getting a list of 1000 items, insert them in the page in intervals of 50, with a small delay between each, so the browser has time to repaint.
YMMV, maybe it looks great as is in Chrome, but freezes for 5 seconds in IE.
Browsers won't typically update images whilst JavaScript code is executing. If you need the spinner to continue animating during DOM population, your population function will have to give up control back to the browser several times a second to let it update the image, typically by setting a timeout (with no delay, or a very short delay) that calls back into the population process, and then returning.
Unfortunately this will usually make your population function much more complicated, as you have to keep track of how far you've got in the population process in variables instead of relying on loops and conditional structures to remember where you are. Also, it will be slightly slower to run, depending on how you're populating the page structures, and if there are click or other events that your application might get delivered half-way through population you can end up with nasty race conditions.
IMO it would probably be better to stop the spinner and then update the DOM. You'll still get the pause, but without the spinner stuttering to a halt it won't be as noticeable. To give the browser a chance to update the spinner after ajaxStop has changed its src, use a zero-delay-timeout-continuation in your AJAX callback function so that on completion the browser gets a chance to display the altered spinner before going into the lengthy population code.
Making this population step faster is definitely worthwhile, if a slightly different topic. (Appending lots of DOM elements one after the other is inherently slow as each operation has to spend more time trudging through list operations. Appending lots of DOM elements all at once via a DocumentFragment is fast, but getting all those DOM elements into the fragment in the first place might not be. Parsing the entire innerHTML at once is generally fast, but generating HTML without injection security holes is an annoyance; serialising and re-parsing via innerHTML+= is slower and totally awful. IE/HTML5 insertAdjacentHTML is fast, but needs fallback implementation for many browsers: ideally fast Range manipulation, falling back to slow node-by-node DOM calls for browsers with no Range. Don't expect jQuery's append to do this for you; it is as slow as node-by-node DOM operations because that's exactly what it's doing.)
While manipulating the DOM on the fly is really tedious for a lot of browser (especially older one) you might want to optimize what you are doing there as much as you can.
Also, another good idea would be to make sure you are running jQuery 1.4 which is a lot faster for doing such operations.
You can see useful benchmark(1.3 vs 1.4) done by the jQuery team that illustrates that here:
http://jquery14.com/day-01/jquery-14