Book Image

Box2D for Flash Games

Book Image

Box2D for Flash Games

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.
Table of Contents (15 chapters)
Box2D for Flash Games
About the Author
About the Reviewers

Trace the beginning and the end of a collision

As the names suggest, the Begin Contact Event is called when two fixtures begin to overlap, while the End Contact Event is called when two fixtures cease to overlap.

  1. Let's analyze the BeginContact function line by line:

    var fixtureA:b2Fixture=contact.GetFixtureA();
    var fixtureB:b2Fixture=contact.GetFixtureB();

    As you can see, BeginContact has a b2Contact object passed as an argument. It contains all collision information we are looking for at the moment. GetFixtureA and GetFixtureB methods return the fixtures involved in the collision. I am saving them in fixtureA and fixtureB variables.

  2. Then, as I am looking for bodies, I need to get the body from a fixture. You should already know about the GetBody method:

    var bodyA:b2Body=fixtureA.GetBody();
    var bodyB:b2Body=fixtureB.GetBody();
  3. Now bodyA and bodyB are the colliding bodies. Time to print some text in the output window:

    trace("first body: "+bodyA.GetUserData());
    trace("second body: "+bodyB.GetUserData...