#### Overview of this book

Physics games are getting more and more popular, and Box2D is the best choice if you are looking for a free, stable and robust library to handle physics. With Box2D you can create every kind of 2D physics game, only coding is not the fun part, but the game itself. "Box2D for Flash Games" will guide you through the process of making a Flash physics game starting from the bare bones and taking you by hand through complex features such as forces, joints and motors. As you are learning, your game will have more and more features, like the physics games you are used to playing. The book analyzes two of the most played physics games, and breaks them down to allow readers to build them from scratch in a step-by-step approach. By the end of the book, you will learn how to create basic primitive bodies as well as complex, compound bodies. Motors will give life to cars, catapults and siege machines firing bullets, while a complete collision management will make your game look even more realistic. If you want to make full Flash games with physics, then Box2D for Flash Games will guide you through the entire process of making a Flash physics game.
Box2D for Flash Games
Credits
www.PacktPub.com
Preface
Free Chapter
Hello Box2D World
Interacting with Bodies
Applying Forces to Bodies
Skinning the Game
Bullets and Sensors
Index

## Creating a box shape

Let's perform the following steps:

1. First, body and fixture definitions can be reassigned to define our new body. This way, we don't need to declare another `bodyDef` variable, but we just need to reuse the one we used for the creation of the sphere by changing its position:

`bodyDef.position.Set(320/worldScale,470/worldScale);`

Now the body definition is located in the horizontal center, and close to the bottom of the screen.

2. To create a polygon shape, we will use the `b2PolygonShape` class:

`var polygonShape:b2PolygonShape=new b2PolygonShape();`

This way we create a polygon shape in the same way we created the circle shape earlier.

3. Polygon shapes must follow some restrictions, but at the moment because we only need an axis-aligned box, the `SetAsBox` method is all we need.

`polygonShape.SetAsBox(320/worldScale,10/worldScale);`

The method requires two arguments: the half-width and the half-height of the box. In the end, our new polygon shape will have its center at pixels (320, 470), and...