A simple pong implementation that runs on IOS.

The following stuff is used to create this Pong implementation for IOS:

• XCode 4.x
• Objective C
• Cocos2D
• Box2D
• Freetime in an hotel in Rotterdam

All real logic and non scaffolding code can be found in three classes.

Main entry point. Bootstraps all the game objects and is the layer where the game is drawn on. It also holds and manages the game score.

The paddle game object. Contains logic to move itself on touch.

The ball game object. It contains logic to respawn.

Box2D works with several fundamental objects. We briefly define these objects here and more details are given later in this document.

A physics world is a collection of bodies, fixtures, and constraints that interact together. Box2D supports the creation of multiple worlds, but this is usually not necessary or desirable.

A 2D geometrical object, such as a circle or polygon.

A chunk of matter that is so strong that the distance between any two bits of matter on the chunk is completely constant. They are hard like a diamond. In the following discussion we use body interchangeably with rigid body.

A fixture binds a shape to a body and adds material properties such as density, friction, and restitution.

A constraint is a physical connection that removes degrees of freedom from bodies. In 2D a body has 3 degrees of freedom (two translation coordinates and one rotation coordinate). If we take a body and pin it to the wall (like a pendulum) we have constrained the body to the wall. At this point the body can only rotate about the pin, so the constraint has removed 2 degrees of freedom.

A special constraint designed to prevent penetration of rigid bodies and to simulate friction and restitution. You do not create contact constraints; they are created automatically by Box2D.

This is a constraint used to hold two or more bodies together. Box2D supports several joint types: revolute, prismatic, distance, and more. Some joints may have limits and motors.

A joint limit restricts the range of motion of a joint. For example, the human elbow only allows a certain range of angles.

A joint motor drives the motion of the connected bodies according to the joint's degrees of freedom. For example, you can use a motor to drive the rotation of an elbow.

I created this for the Devnology Code Fest. using XCode, ObjC and the Cocos2D Box2d framework.