AS3: How accurate are the getTimer() method and the Timer class?

Question

I\'m in the process of making a game (a shmup) and I\'ve started to question the accuracy of the timers in ActionScript. Sure, they\'re accurate enough when you want to tim

Answer 1

I just tried running your sample code, exactly as-is except as a frame script, and where I'm sitting Timer works exactly as you'd expect. With a 30ms timer, the average comes out about 33-34, and with a 3ms timer it comes out around 3.4 or 3.5. With a 1 ms timer I get between 1.4 and 1.6 over a thousand trials. It works that way in Flash and in the browser.

So as for the accuracy, see Tinic's blog post in Luke's answer. But for the upper limit on frequency, if you're getting events no faster than 16ms apart with only the sample code you posted, either something's weird, or maybe that's the upper limit on how fast your browser is giving Flash timing messages. If you're getting those results in your actual game, I think you simply have synchronous code that blocking the timer events.

One more thing - I know it's not what you asked, but it would really be wiser to handle your game logic in an ENTER_FRAME handler. It doesn't matter whether the code to spawn lasers runs every 30ms or every 3ms, the screen only gets redrawn once per frame (unless you're forcing it to update more often, which you probably shouldn't be). So whatever happens between screen refreshes is just overhead that lowers your overall framerate, since with a little cleverness it ought to be possible to achieve the exact same results as you'd get from a timer that executed more frequently. For example, instead of spawning a laser every 3ms, you could spawn 10 lasers every 30ms, and move each one a certain distance along its flight path, as if it had been created 3 or 6 or 9ms earlier.

Another natural way to run your logic off frame events would be to make a game loop that "theoretically" runs every T milliseconds. Then, in your ENTER_FRAME handler, simply iterate that loop F/T times, where F is the number of ms that have elapsed since the last frame event. Thus if you want the game to theoretically update every 5ms, and you want the screen to update at 30FPS, you'd simply publish at 30FPS, and in your ENTER_FRAME handler you'd call your main game loop 5-7 times consecutively, depending on how long it had been since the last frame. Onscreen, this will give you the same results as if you had used a 5ms timer event, and it will dispense with much of the overhead.