Let system time determine animation speed, not program FPS

Question

I'm writing a card game in ActionScript 3. Each card is represented by an instance of a class extending movieclip exported from Flash CS4 that contains the card graphics and a flip animation. When I want to flip a card I call gotoAndPlay on this movieclip.

When the frame rate slows down all animations take longer to finish. It seems Flash will by default animate movieclips in a way that makes sure all frames in the clip will be drawn. Therefor, when the program frame rate goes below the frame rate of the clip, the animation will be played at a slower pace.

I would like to have an animation always play at the same speed and as a consequence always be shown on the screen for the same amount of time. If the frame rate is too slow to show all frames, frames are dropped. Is is possible to tell Flash to animate in this way? If not, what is the easiest way to program this behavior myself?

Answer 1

The easiest way would be to use a Timer (or a setInterval) triggering every 1000/fps milliseconds, telling your MovieClip to go to its next frame.

If you need something more accurate, you'll have to check the time spent since the last update (stolen from the first comment of this article from Keith Peters' blog, which explains everything pretty well).

Answer 2

It's been a while since I used Flash but from what I understand it's not possible because Flash uses a frame based animation model.

Silverlight however uses a time based animation model and will just draw as many intermediate frames as the frame-rate allows.

Answer 3

The tween class (fl.transitions.Tween) is perfect for this situation. By setting the last argument of the constructor to TRUE then it bases its animations/triggers off of seconds, and as far as I know it compensates for FPS loss/gain.

You can easily use it like the Timer class by passing a new object (Trigger(new Object(), "x") to the constructor and creating a listener for MOTION_FINISH (TweenEvent.MOTION_FINISH) to trigger your event!

I use Tweens for a LOT of things because they're easy, fast, and supported by everything. And like I said, it should solve your FPS/lag issues since it adjusts to FPS changes in real-time (as far as I know!).