The Essential Guide to Physics for Flash Games, Animation, and Simulations

Producing animation using code

There are a number of ways to produce animation using code in AS3.0. For example, there is a Tween class that can be used to move, resize, and fade movie clips. However, our focus is to produce physics-based animation. We basically know how to move objects. What is needed is a method to measure the advancement of time. We need a clock.

Using the built-in frame stepping as a clock

We've already been using a clock: the ENTER_FRAME event. Let's now take a closer look to see how good a time-keeper the ENTER_FRAME event is.

Suppose the frame rate of a movie is 50 fps. This means that, in theory, the Event.ENTER_FRAME event is triggered once every 1/50 seconds (every 20 milliseconds). We said “in theory” because the frame ...