Creation of a Flash Stabilize! clone using Box2D – part 1

package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
	import Box2D.Dynamics.*;
	import Box2D.Collision.*;
	import Box2D.Collision.Shapes.*;
	import Box2D.Common.Math.*;
	public class stabilize extends Sprite {
		public var m_sprite: Sprite = new Sprite();
		public var m_world:b2World;
		public var initX:Number=0.0;
		public var initY:Number=0.0;
		public var drawing:Boolean=false;
		public function stabilize() {
			var gravity:b2Vec2=new b2Vec2(0,9.8);
			var worldAABB:b2AABB = new b2AABB();
			worldAABB.lowerBound.Set(-1000,-1000);
			worldAABB.upperBound.Set(1000,1000);
			m_world=new b2World(worldAABB,gravity,true);
			m_sprite = new Sprite();
			addChild(m_sprite);
			debug_draw();
			AddBox(250/30,350/30,10/30,10/30,0);
			AddBox(250/30,350/30,200/30,10/30,20);
			addEventListener(Event.ENTER_FRAME,Update);
			stage.addEventListener(MouseEvent.MOUSE_DOWN,mousePressed);
			stage.addEventListener(MouseEvent.MOUSE_MOVE,mouseMoved);
			stage.addEventListener(MouseEvent.MOUSE_UP,mouseReleased);
		}
		public function mousePressed(e:MouseEvent) {
			//Store initial X and Y position
			initX=e.localX;
			initY=e.localY;
			drawing=true;
		}
		public function mouseMoved(e:MouseEvent) {
			if (drawing) {
				//Simply draw the "ghost" of the box we are about to add
				graphics.clear();
				graphics.beginFill(0xFF0000,0.5);
				graphics.drawRect(initX,initY,e.localX-initX,e.localY-initY);
			}
		}
		public function mouseReleased(e:MouseEvent) {
			graphics.clear();
			drawing=false;
 
			//Coordinates of bottom-right of box (when drawing from left to right)
			var finalX:Number=e.localX;
			var finalY:Number=e.localY;
 
			//Correct if drawing from right to left
			if (finalX<initX) {
				//If so, swap initX and finalX
				var tempX:Number=initX;
				initX=finalX;
				finalX=tempX;
			}
			if (finalY<initY) {
				//If so, swap initY and finalY
				var tempY:Number=initY;
				initY=finalY;
				finalY=tempY;
			}
			//Work out the half-width and height of the box
			var boxHalfWidth:Number = Math.abs((finalX-initX)/2);
			var boxHalfHeight:Number = Math.abs((finalY-initY)/2);
			if (boxHalfWidth>0&&boxHalfHeight>0) {
				AddBox((finalX-boxHalfWidth)/30,(finalY-boxHalfHeight)/30,boxHalfWidth/30,boxHalfHeight/30,1);
			}
		}
		/*
		NOTE: AddBox takes the _x,_y and halfwidth and halfheight parameters
		in METRES not PIXELS. This means when you call this function, always
		DIVIDE a pixel size by 30 to get it in meteres.
		*/
		public function AddBox(_x:Number,_y:Number,_halfwidth:Number,_halfheight:Number,density:Number) {
			var bodyDef:b2BodyDef = new b2BodyDef();
			bodyDef.position.Set(_x,_y);
			var boxDef:b2PolygonDef = new b2PolygonDef();
			boxDef.SetAsBox(_halfwidth,_halfheight);
			boxDef.density=density;
			boxDef.friction=0.3;
			boxDef.restitution=0.2;
			var body:b2Body=m_world.CreateBody(bodyDef);
			body.CreateShape(boxDef);
			body.SetMassFromShapes();
		}
		public function Update(e:Event) {
			//We need to do this to simulate physics
			m_world.Step(1/30,10);
		}
		public function debug_draw() {
			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;
			m_world.SetDebugDraw(dbgDraw);
 
		}
	}
}