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Box2DFlash 2.1a Update Notes


One of the biggest changes is how shapes work. Material properties of shapes, such as density, friction, etc, have been separated from geometric properties (the radius, vertices etc). The former are now fixtures, while the latter remains in shapes.

After creating a body, you should create fixture definition for material properties. You provide the shape to the fixture, and call b2Body.CreateFixture:

var fd:b2FixtureDef = new b2FixtureDef();
fd.density = 1.0;
fd.shape = new b2CircleShape(5.0);
var fixture:b2Fixture = myBody.CreateFixture(fd);

For convenience, b2Body.CreateFixture2 allows you to skip creating a b2FixtureDef, providing just a shape and (optional) density.

var fixture:b2Fixture = myBody.CreateFixture2(new b2CircleShape(5.0), 1.0);

Note that b2CircleShape and b2PolygonShape are used directly - there is no b2ShapeDef.

Body types

In 2.0, there were two sorts of bodies - static and dynamic. The mass determined if a body was static or not. Now a new type has been added, kinematic, for bodies that should move but not be pushed by other bodies. To account for this, you must set the body's type correctly using b2BodyDef.type and b2Body.SetType:

var bd:b2BodyDef = new b2BodyDef();
bd.type = b2Body.b2_dynamicBody;


2.0's collision event system was very hard to use, and has been replace. Events are now not per-contact-point, but per-contact. They provide a manifold containing information including the contact points. BeginContact and EndContact are provided for easily determining when two objects begin and end touching, and are the only events raised by sensors. Please see the reference section for more details.


2.1 has a completely rewritten broadphase. It is now not necessary to specify a size for your world, it'll always be large enough.

Game Loop

Though likely to change for the final release, it is now necessary to call b2World.ClearForces() immediately after b2World.Step. This is to facilitate users who wish have multiple b2World.Steps between one game logic step, for the purposes of stability. You may also need to call b2World.DrawDebugData() if you are using debug drawing.


Several restrictions have been lifted.