A commenter on hacks.mozilla.org suggested that instead of the pattern of adding a MozBeforePaint Listener and then calling mozRequestAnimationFrame, it would be slightly simpler if mozRequestAnimationFrame took a callback parameter that would be run at the next frame and then discarded. So the example here: http://hacks.mozilla.org/2010/08/more-efficient-javascript-animations-with-mozrequestanimationframe/ would become var start = window.mozAnimationStartTime; function step(event) { var progress = event.timeStamp - start; d.style.left = Math.min(progress/10, 200) + "px"; if (progress < 2000) { window.mozRequestAnimationFrame(step); } } window.mozRequestAnimationFrame(step); which is a bit simpler and avoids the possibility of the author forgetting to unregister the event listener. We could leave the MozBeforePaint event support in --- it's likely to be useful for other things --- and make the callback parameter optional, so authors could use either pattern.

I suppose the callback should probably just take the timestamp as a parameter, so the example would be var start = window.mozAnimationStartTime; function step(timeStamp) { var progress = timeStamp - start; d.style.left = Math.min(progress/10, 200) + "px"; if (progress < 2000) { window.mozRequestAnimationFrame(step); } } window.mozRequestAnimationFrame(step);

I guess we need to get this in for beta6 if we get it in at all. If it slips, we can do it post-FF4.

Comment on attachment 473384 [details] [diff] [review] Make it possible to pass an explicit callback function to mozRequestAnimationFrame. I made sure that if you only use the callback version we don't also fire the event. If it's ok to fire the event in addition to calling the callbacks, then I can probably simplify the code a little bit... but this seemed like cleaner api for web pages.

(In reply to comment #4) > I made sure that if you only use the callback version we don't also fire the > event. If it's ok to fire the event in addition to calling the callbacks, then > I can probably simplify the code a little bit... but this seemed like cleaner > api for web pages. Actually I think we should fire the event for every paint.

(In reply to comment #5) > Actually I think we should fire the event for every paint. I mean, not now, but eventually.

Comment on attachment 473384 [details] [diff] [review] Make it possible to pass an explicit callback function to mozRequestAnimationFrame. Is that the right place for nsIAnimationFrameListener? I expected dom/interfaces somewhere. ForgetAnimationFrameListeners should be called TakeAnimationFrameListeners, maybe? Why does ScheduleAnimationFrameListeners return a value? I suggest it can just return void. This should probably get super-review. Hopefully dbaron's around...

Comment on attachment 473384 [details] [diff] [review] Make it possible to pass an explicit callback function to mozRequestAnimationFrame. Do the other [function] interfaces exposed to the Web not have classinfo? It seems a little odd, but I guess I can't see how it's harmful. Put a newline at the end of the file, though.

> Do the other [function] interfaces exposed to the Web not have classinfo? Yes. Classinfo is per-implementation, and the only expected implementation of this interface is a JS Function object. Classinfo doesn't even make sense there. > Put a newline at the end of the file, though. Done.

> Actually I think we should fire the event for every paint. Per irc discussion, leaving this part as is for now. > Is that the right place for nsIAnimationFrameListener? Excellent question. I could put it in dom/interface/base, I suppose. We don't have a good dumping ground for that sort of thing. > ForgetAnimationFrameListeners should be called TakeAnimationFrameListeners, Sold. > Why does ScheduleAnimationFrameListeners return a value? It doesn't really need to given the existing consumer code, but if we ever want to know whether the listener really got added... I can remove it for now; easy enough to restore if we need it.

Pushed http://hg.mozilla.org/mozilla-central/rev/c05c386324c0

I've updated the doc here: https://developer.mozilla.org/en/DOM/window.mozRequestAnimationFrame