Classes
 ClassDescription
 b2CircleDef This structure is used to build circle shapes.
 b2CircleShape 
 b2FilterData This holds contact filtering data.
 b2MassData This holds the mass data computed for a shape.
 b2PolygonDef 
 b2PolygonShape Convex polygon.
 b2Shape A shape is used for collision detection.
 b2ShapeDef A shape definition is used to construct a shape.