Box2D for Flash Games

Physics games aren't just a matter of physics

This section has nothing to do with Box2D, and it's just necessary to allow the player to launch the bird. So I am explaining what happens here very quickly, in order to go straight to the point.

Before we start drawing, I want you to know that you can mix physics and non-physics scripts in your game, just like I am doing now. In this case, player interaction is not managed by Box2D, which comes into play once the bird is released.

First, we need some more class-level variables:

private var world:b2World;
private var worldScale:Number=30;
private var theBird:Sprite=new Sprite();
private var slingX:int=100;
private var slingY:int=250;
private var slingR:int=75;

theBird is the sprite representing the ...