Game Development Reference
In-Depth Information
Joints and Motors
All kinds of bodies you've met until now have something in common: they are free
and do not depend on each other, unless they collide. Sometimes you may want to
constrain bodies to each other. If you think about Crush the Castle game, the siege
machine is made by a series of bodies connected together in some way.
Box2D allows us to create constraints between bodies with
joints
. Joints allow us to
build complex objects and give more realism to our games.
In this chapter you will learn how to create the most common types of joints, and
you will discover, among other things, how to:
• Pick, drag, and drop bodies with mouse joints
• Keep bodies at a given distance with distance joints
• Make bodies rotate using revolute joints
• Give life to your games using motors
By the end of the chapter, you will be able to destroy the Angry Birds level with a
siege machine.
Anyway, joints can also be used to interact with bodies, by picking and dragging
them with the mouse. This is the first joint you are about to learn.
Picking and dragging bodies - mouse
joints
Hard things first; we are going to start with one of the most difficult joints. Sad but
necessary, as it will allow us to create and test other joints easily.
