Box2DFlash 2.1a released – what changed

January 27, 2010 • Actionscript 3, Box2D, Flash by Emanuele Feronato • 19 Comments

Some days ago Boris the Brave released the new version of the popular physics library.

There are some critical changes that won’t make old projects run in the new environment.

The most important ones are:

  • It is now not necessary to specify a size for your world, it’ll always be large enough.
  • Improved collisions system
  • You must specify if a body is dynamic, no matter if its mass is greater than zero
  • Fixtures now determine material properties of shapes, such as density, friction and so on

But I think an example will be more explicative than a thousand words, so I created a simple vehicle you can control with left and right arrow keys. It uses revolute joints and motors.

This is the code you would need in the old Box2D version

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package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.KeyboardEvent;
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Collision.Shapes.*;
	import Box2D.Common.Math.*;
	import Box2D.Dynamics.Joints.*;
	public class car extends Sprite {
		public var world:b2World;
		public var car_body:b2Body;
		public var front_wheel:b2Body;
		public var rear_wheel:b2Body;
		public var front_motor:b2RevoluteJointDef = new b2RevoluteJointDef();
		public var rear_motor:b2RevoluteJointDef = new b2RevoluteJointDef();
		public var rear_motor_added:b2RevoluteJoint
		public var front_motor_added:b2RevoluteJoint
		public function car():void {
			// world setup
			var worldAABB:b2AABB = new b2AABB();
			worldAABB.lowerBound.Set(-100, -100);
			worldAABB.upperBound.Set(100, 100);
			world=new b2World(worldAABB,new b2Vec2(0,10.0),true);
			debug_draw();
			// variables used for bodies and motors
			var body:b2Body;
			var bodyDef:b2BodyDef= new b2BodyDef();
			var boxDef:b2PolygonDef = new b2PolygonDef();
			var circleDef:b2CircleDef= new b2CircleDef();
			var revoluteJointDef:b2RevoluteJointDef = new b2RevoluteJointDef();
			// adding the ground
			bodyDef.position.Set(250/30, 200/30);
			boxDef.SetAsBox(600/30, 20/30);
			boxDef.friction=1;
			boxDef.density=0;
			body=world.CreateBody(bodyDef);
			body.CreateShape(boxDef);
			body.SetMassFromShapes();
			bodyDef.position.Set(0/30, 200/30);
			boxDef.SetAsBox(50/30, 50/30);
			boxDef.friction=1;
			boxDef.density=0;
			body=world.CreateBody(bodyDef);
			body.CreateShape(boxDef);
			body.SetMassFromShapes();
			bodyDef.position.Set(500/30, 200/30);
			boxDef.SetAsBox(50/30, 50/30);
			boxDef.friction=1;
			boxDef.density=0;
			body=world.CreateBody(bodyDef);
			body.CreateShape(boxDef);
			body.SetMassFromShapes();
			// adding car body
			bodyDef.position.Set(250/30, 90/30);
			car_body=world.CreateBody(bodyDef);
			boxDef.density=1;
			boxDef.friction=1;
			boxDef.restitution=0.1;
			boxDef.SetAsBox(50/30, 10/30);
			car_body.CreateShape(boxDef);
			car_body.SetMassFromShapes();
			// adding wheels
			circleDef.radius=20/30;
			circleDef.density=1;
			circleDef.friction=5;
			circleDef.restitution=0.1;
			// front wheel
			bodyDef.allowSleep = false;
			bodyDef.position.Set(car_body.GetWorldCenter().x + 40/30, car_body.GetWorldCenter().y);
			front_wheel=world.CreateBody(bodyDef);
			front_wheel.CreateShape(circleDef);
			front_wheel.SetMassFromShapes();
			// rear wheel
			bodyDef.position.Set(car_body.GetWorldCenter().x - 40/30, car_body.GetWorldCenter().y);
			rear_wheel=world.CreateBody(bodyDef);
			rear_wheel.CreateShape(circleDef);
			rear_wheel.SetMassFromShapes();
			// front joint
			front_motor.enableMotor=true;
			front_motor.maxMotorTorque=10;
			front_motor.Initialize(car_body, front_wheel, front_wheel.GetWorldCenter());
			front_motor_added=world.CreateJoint(front_motor) as b2RevoluteJoint;
			// rear joint
			rear_motor.enableMotor=true;
			rear_motor.maxMotorTorque=1;
			rear_motor.Initialize(car_body, rear_wheel, rear_wheel.GetWorldCenter());
			rear_motor_added=world.CreateJoint(rear_motor) as b2RevoluteJoint;
			//
			addEventListener(Event.ENTER_FRAME, update);
			stage.addEventListener(KeyboardEvent.KEY_DOWN, key_down);
		}
		public function key_down(event:KeyboardEvent):void {
			switch (event.keyCode) {
				case 39 :
					rear_motor_added.SetMotorSpeed(10);
					front_motor_added.SetMotorSpeed(10);
					break;
				case 37 :
					rear_motor_added.SetMotorSpeed(-10);
					front_motor_added.SetMotorSpeed(-10);
					break;
			}
		}
		public function debug_draw():void {
			var m_sprite:Sprite;
			m_sprite = new Sprite();
			addChild(m_sprite);
			var dbgDraw:b2DebugDraw = new b2DebugDraw();
			var dbgSprite:Sprite = new Sprite();
			m_sprite.addChild(dbgSprite);
			dbgDraw.m_sprite=m_sprite;
			dbgDraw.m_drawScale=30;
			dbgDraw.m_alpha=1;
			dbgDraw.m_fillAlpha=0.5;
			dbgDraw.m_lineThickness=1;
			dbgDraw.m_drawFlags=b2DebugDraw.e_shapeBit;
			world.SetDebugDraw(dbgDraw);
		}
		public function update(e : Event):void {
			world.Step(1/30, 10);
		}
	}
}

Take a look at the compiler errors…

And this is the new one. All changes are commented.

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package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.KeyboardEvent;
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Collision.Shapes.*;
	import Box2D.Common.Math.*;
	import Box2D.Dynamics.Joints.*;
	public class car extends Sprite {
		public var world:b2World;
		public var car_body:b2Body;
		public var front_wheel:b2Body;
		public var rear_wheel:b2Body;
		public var front_motor:b2RevoluteJointDef = new b2RevoluteJointDef();
		public var rear_motor:b2RevoluteJointDef = new b2RevoluteJointDef();
		// this is new!!!
		public var fixtureDef:b2FixtureDef = new b2FixtureDef();
		public var rear_motor_added:b2RevoluteJoint;
		public var front_motor_added:b2RevoluteJoint;
		public function car():void {
			// world setup
			/*var worldAABB:b2AABB = new b2AABB();
			worldAABB.lowerBound.Set(-100, -100);
			worldAABB.upperBound.Set(100, 100);*/
			world=new b2World(new b2Vec2(0,10.0),true);// was world=new b2World(worldAABB,new b2Vec2(0,10.0),true);
			debug_draw();
			// variables used for bodies and motors
			var body:b2Body;
			var bodyDef:b2BodyDef= new b2BodyDef();
			var boxDef:b2PolygonShape = new b2PolygonShape();// was var boxDef:b2PolygonDef = new b2PolygonDef();
			var circleDef:b2CircleShape=new b2CircleShape(20/30);// was var circleDef:b2CircleDef = new b2CircleDef();
			var revoluteJointDef:b2RevoluteJointDef = new b2RevoluteJointDef();
			// adding the ground
			bodyDef.position.Set(250/30, 200/30);
			boxDef.SetAsBox(600/30, 20/30);
			// this is new!!
			fixtureDef.shape=boxDef;
			fixtureDef.friction=1;// was boxDef.friction=1;
			fixtureDef.density=1;// was boxDef.density=0;
			body=world.CreateBody(bodyDef);
			body.CreateFixture(fixtureDef);// was body.CreateShape(boxDef);
			// remove: body.SetMassFromShapes();
			bodyDef.position.Set(0/30, 200/30);
			boxDef.SetAsBox(50/30, 50/30);
			fixtureDef.shape=boxDef;
			fixtureDef.friction=1;// was boxDef.friction=1;
			fixtureDef.density=1;// was boxDef.density=0;
			body=world.CreateBody(bodyDef);
			body.CreateFixture(fixtureDef);// was body.CreateShape(boxDef);
			// remove: body.SetMassFromShapes();
			bodyDef.position.Set(500/30, 200/30);
			boxDef.SetAsBox(50/30, 50/30);
			// this is new!!
			fixtureDef.shape=boxDef;
			fixtureDef.friction=1;// was boxDef.friction=1;
			fixtureDef.density=1;// was boxDef.density=0;
			body=world.CreateBody(bodyDef);
			body.CreateFixture(fixtureDef);// was body.CreateShape(boxDef);
			// remove: body.SetMassFromShapes();
			// adding car body
			bodyDef.position.Set(250/30, 90/30);
			// this is new!!
			bodyDef.type=b2Body.b2_dynamicBody;
			boxDef.SetAsBox(50/30, 10/30);
			// this is new!!
			fixtureDef.shape=boxDef;
			fixtureDef.density=1;// was boxDef.density=1;
			fixtureDef.friction=1;// was boxDef.friction=1;
			fixtureDef.restitution=0.1;// was boxDef.restitution=0.1;
			car_body=world.CreateBody(bodyDef);
			car_body.CreateFixture(fixtureDef);// was body.CreateShape(boxDef);
			// remove: car_body.SetMassFromShapes();
			// adding wheels
			// remove: circleDef.radius=20/30;
			fixtureDef.density=1;// was circleDef.density=1;
			fixtureDef.friction=5;// was circleDef.friction=5;
			fixtureDef.density=0.1;// was circleDef.restitution=0.1;
			// this is new!!
			fixtureDef.shape=circleDef;
			// front wheel
			bodyDef.allowSleep=false;
			bodyDef.position.Set(car_body.GetWorldCenter().x + 40/30, car_body.GetWorldCenter().y);
			front_wheel=world.CreateBody(bodyDef);
			front_wheel.CreateFixture(fixtureDef);// was front_wheel.CreateShape(circleDef);
			// remove: front_wheel.SetMassFromShapes();
			// rear wheel
			bodyDef.position.Set(car_body.GetWorldCenter().x - 40/30, car_body.GetWorldCenter().y);
			rear_wheel=world.CreateBody(bodyDef);
			rear_wheel.CreateFixture(fixtureDef);// was rear_wheel.CreateShape(circleDef);
			// remove: rear_wheel.SetMassFromShapes();
			// front joint
			front_motor.enableMotor=true;
			front_motor.maxMotorTorque=10;
			front_motor.Initialize(car_body, front_wheel, front_wheel.GetWorldCenter());
			front_motor_added=world.CreateJoint(front_motor) as b2RevoluteJoint;
			// rear joint
			rear_motor.enableMotor=true;
			rear_motor.maxMotorTorque=1;
			rear_motor.Initialize(car_body, rear_wheel, rear_wheel.GetWorldCenter());
			rear_motor_added=world.CreateJoint(rear_motor) as b2RevoluteJoint;
			//
			addEventListener(Event.ENTER_FRAME, update);
			stage.addEventListener(KeyboardEvent.KEY_DOWN, key_down);
		}
		public function key_down(event:KeyboardEvent):void {
			switch (event.keyCode) {
				case 39 :
					rear_motor_added.SetMotorSpeed(10);
					front_motor_added.SetMotorSpeed(10);
					break;
				case 37 :
					rear_motor_added.SetMotorSpeed(-10);
					front_motor_added.SetMotorSpeed(-10);
					break;
			}
		}
		public function debug_draw():void {
			var m_sprite:Sprite;
			m_sprite = new Sprite();
			addChild(m_sprite);
			var dbgDraw:b2DebugDraw = new b2DebugDraw();
			var dbgSprite:Sprite = new Sprite();
			m_sprite.addChild(dbgSprite);
			dbgDraw.SetSprite(m_sprite); // was dbgDraw.m_sprite=m_sprite;
			dbgDraw.SetDrawScale(30); // was dbgDraw.m_drawScale=30;
			//dbgDraw.SetAlpha(1); // was dbgDraw.m_alpha=1;
			dbgDraw.SetFillAlpha(0.5); // was dbgDraw.m_fillAlpha=0.5;
			dbgDraw.SetLineThickness(1); // was dbgDraw.m_lineThickness=1;
			dbgDraw.SetFlags(b2DebugDraw.e_shapeBit); // was dbgDraw.m_drawFlags=b2DebugDraw.e_shapeBit;
			world.SetDebugDraw(dbgDraw);
		}
		public function update(e : Event):void {
			world.Step(1/30,10,10);// was world.Step(1/30, 10);
			// this is new!
			world.ClearForces() 
			// this is new!!
			world.DrawDebugData();
		}
	}
}

Download the source code, new library included.

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This post has 19 comments

  1. Luiz Fernando

    on January 27, 2010 at 5:33 pm

    Hmm nice. I’ll check it to see if there was any substantial changes on the engine itself…

  2. Bindiry

    on January 27, 2010 at 8:53 pm

    I only hope release it early.

  3. Vlad

    on January 28, 2010 at 7:43 am

    So basically, Emanuelle, if we try to use this version of box2das3 with your previous tutorials… ouch.

  4. Rackdoll

    on January 28, 2010 at 2:38 pm

    thnx for this tut. Was wondering what i did wrong with all those compiler errors. Now i see the finer of it. Good.
    Keep on the tuts \o/

    Rackdoll

  5. ricky

    on January 28, 2010 at 3:11 pm

    Actually, I was about to learn Box2d yesterday and grabbed a copy of your Box2d for absolute beginners when I got surprised that I got lots of errors.I was really disappointed…how come the hello world of Borris don’t seem to work?

    Will you do a Box2d for absolute beginners the updated version. I was really waiting for your post on the new Box2d changes. Thanks you make complicated things sound simple.You could be a professor.:)

  6. rishabh

    on January 28, 2010 at 5:19 pm

    @ricky
    he is like a professor to me

    i liked the fixtures and all
    got major reusability made now

    but i think we need another begginer tut on this =[

    about the old projects thing

    if you have time rename the new version to Box2DA and then change it each and every class
    thats what i did so my older projects work (they are not that old but i downloaded the new source today)

  7. Monkios

    on January 28, 2010 at 9:25 pm

    Nice …

    So the guy made a version of his thing wich is not backward-compatible ?

    How unuseful !

  8. rishabh

    on January 29, 2010 at 1:00 pm

    minkios:
    it isn’t unuseful at all , it has a lot of changes which help,though i haven’t looked into all

  9. ozdy

    on January 30, 2010 at 9:18 pm

    Hi guys, sounds great.
    Any idea if the flash 10 version has performance enhancements (like using vectors)?

  10. Oscar

    on January 31, 2010 at 4:27 am

    HI, looks some code is gone, like boundaryListener how this works now? some idea? Thanks.

  11. akipponn

    on February 1, 2010 at 12:03 pm

    Hi, what a great entry! This page is so helpful.

    from Kyoto, Japan :-)

  12. Box2dflash 2.1a ??????????????????????? | aki note

    on February 1, 2010 at 12:58 pm

    [...] Box2dflash ? C++ ??????????? Box2d ? Flash ??????????????2008 ??????????????????????????????????????????????????????????????????????????????????? BOX2DFLASH 2.1A RELEASED – WHAT CHANGED @ EMANUELE FERONATO » italian geek and PROgrammer http://www.emanueleferonato.com/2010/01/27/box2dflash-2-1a-released-what-changed/ [...]

  13. box2d flash new release + a minimal sample | aki note

    on February 1, 2010 at 1:58 pm

    [...] http://www.emanueleferonato.com/2010/01/27/box2dflash-2-1a-released-what-changed/ [...]

  14. Box2D tutorial for the absolute beginners – revamped : Emanuele Feronato - italian geek and PROgrammer

    on February 2, 2010 at 1:01 am

    [...] 2.1 release, a lot of things changed, so it’s time to publish another tutorial for the absolute [...]

  15. Create incredible particle effects with Partigen 2 : Emanuele Feronato - italian geek and PROgrammer

    on February 8, 2010 at 12:22 pm

    [...] In this example, I am going to create a particle effect with the user interface provided in the component, then I’ll export it with XML and finally add it “on the fly” to the Box2D car example. [...]

  16. Understanding Box2D’s one-way platforms, aka CLOUDS : Emanuele Feronato - italian geek and PROgrammer

    on March 2, 2010 at 1:24 am

    [...] of the new features introduced with Box2D 2.1a is the improved contact listener class which comes in hand when we want to create one-way [...]

  17. sergey

    on April 28, 2010 at 7:37 pm

    please explain how works new collisions and how a i can catch them

  18. la

    on November 22, 2010 at 4:39 am

    You really saved newbies’ lives!

  19. Viktor

    on September 4, 2011 at 8:12 pm

    mistake on line 80

    80 fixtureDef.density=0.1;// was circleDef.restitution=0.1;

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