#### 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 any kind of convex polygons

Box2D allows you to create any kind of polygon shape, as long as the polygon is convex, which means it must have all interior angles less than 180 degrees, so all the vertices point away from the center, and you provide its vertices in clockwise order.

1. First, let's create a vector to store all vertices:

`var vertices:Vector.<b2Vec2>=new Vector.<b2Vec2>();`
2. Then we will push all vertices in clockwise order, as `b2Vec2` objects, specifying the relative position of the vertices to the center of the idol body.

```vertices.push(new b2Vec2(-15/worldScale,-25/worldScale));
vertices.push(new b2Vec2(0,-40/worldScale));
vertices.push(new b2Vec2(15/worldScale,-25/worldScale));
vertices.push(new b2Vec2(0,-10/worldScale));```
3. The previous lines of code are the four vertices of idol's head. Now let's turn this vector into a polygon shape:

`polygonShape.SetAsVector(vertices,4);`

The `SetAsVector` method turns any vector of clockwise vertices into a polygon shape. The second...