在给Box2DFlash中的形状赋予纹理之前，缺省采用DebugDraw方式绘制形状。DebugDraw由若干标志位组成：
e_shapeBit：绘制形状轮廓
e_jointBit：绘制关节的节点和连接线
e_aabbBit：绘制轴对齐边界框（axis aligned bounding boxes）
e_controllerBit：绘制控制器
e_pairBit: 绘制宽相对
e_centerOfMassBit：绘制质量的中心
示例代码如下：
package{
import Box2D.Collision.Shapes.b2CircleShape;
import Box2D.Collision.Shapes.b2PolygonShape;
import Box2D.Collision.Shapes.b2Shape;
import Box2D.Collision.b2AABB;
import Box2D.Common.Math.b2Vec2;
import Box2D.Dynamics.Joints.b2MouseJoint;
import Box2D.Dynamics.Joints.b2MouseJointDef;
import Box2D.Dynamics.b2Body;
import Box2D.Dynamics.b2BodyDef;
import Box2D.Dynamics.b2DebugDraw;
import Box2D.Dynamics.b2Fixture;
import Box2D.Dynamics.b2FixtureDef;
import Box2D.Dynamics.b2World;
import flash.display.Sprite;
import flash.events.Event;
import flash.events.MouseEvent;
[SWF(width=”800″,height=”600″,frameRate=”32″,backgroundColor=”0x000000″)]
public class DebugDraw extends Sprite{
private var world:b2World;
private var body:b2Body;
private var timeStep:Number;
private var iterations:uint;
private var pixelsPerMeter:Number = 30;
private var mouseJoint:b2MouseJoint;
private var mousePVec:b2Vec2 = new b2Vec2();
public function DebugDraw(){
createWorld();
makeDebugDraw();
createWall();
createBodies();
addEventListener(Event.ENTER_FRAME,onEnterframe);
stage.addEventListener(MouseEvent.MOUSE_DOWN,onMouseDown);
stage.addEventListener(MouseEvent.MOUSE_UP,onMouseUp);
}
private function createWorld():void{
var gravity:b2Vec2 = new b2Vec2(0.0,9.8);
var doSleep:Boolean = true;
world = new b2World(gravity,doSleep);
world.SetWarmStarting(true);
timeStep = 1.0/30.0;
iterations = 10;
}
private function makeDebugDraw():void{
var debugDraw:b2DebugDraw = new b2DebugDraw();
var debugSprite:Sprite = new Sprite();
addChild(debugSprite);
debugDraw.SetSprite(debugSprite);
debugDraw.SetDrawScale(30.0);
debugDraw.SetFillAlpha(0.5);
debugDraw.SetLineThickness(1.0);
debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit |
b2DebugDraw.e_controllerBit | b2DebugDraw.e_aabbBit |
b2DebugDraw.e_centerOfMassBit | b2DebugDraw.e_pairBit);
world.SetDebugDraw(debugDraw);
}
private function createWall():void{
var bodyDef:b2BodyDef = new b2BodyDef();
// Body的中心点
bodyDef.position.Set(400/pixelsPerMeter,585/pixelsPerMeter);
body = world.CreateBody(bodyDef);
var shape:b2PolygonShape = new b2PolygonShape();
// 几何体的半宽和半高
shape.SetAsBox(400/pixelsPerMeter,15/pixelsPerMeter);
body.CreateFixture2(shape);
}
private function createBodies():void{
for(var i:int=0;i<10;i++){
var bodyDef:b2BodyDef = new b2BodyDef();
bodyDef.type = b2Body.b2_dynamicBody;
bodyDef.position.x = (Math.random()*600+120)/pixelsPerMeter;
bodyDef.position.y = (Math.random()*150)/pixelsPerMeter;
var hx:Number = (Math.random()*30+15)/pixelsPerMeter;
var hy:Number = (Math.random()*30+15)/pixelsPerMeter;
var fixtureDef:b2FixtureDef = new b2FixtureDef();
fixtureDef.density = 1.0;
fixtureDef.friction = 0.5;
fixtureDef.restitution = 0.2;
if(Math.random()<0.5){
var square:b2PolygonShape = new b2PolygonShape();
square.SetAsBox(hx,hy);
fixtureDef.shape = square;
body = world.CreateBody(bodyDef);
body.CreateFixture(fixtureDef);
}
else{
var circle:b2CircleShape = new b2CircleShape();
circle.SetRadius(hx);
fixtureDef.shape = circle;
body = world.CreateBody(bodyDef);
body.CreateFixture(fixtureDef);
}
}
}
private function onMouseDown(e:MouseEvent):void{
var body:b2Body = getBodyAtMouse();
if(body){
// 建立MouseJoint定义
var mouseJointDef:b2MouseJointDef = new b2MouseJointDef();
// bodyA为无碰撞检测的静态刚体
mouseJointDef.bodyA = world.GetGroundBody();
// bodyB为当前检测到被点击的刚体
mouseJointDef.bodyB = body;
// 设置MouseJoint的最初世界位置
mouseJointDef.target.Set(mouseX/pixelsPerMeter,mouseY/pixelsPerMeter);
mouseJointDef.maxForce = 30000;
mouseJoint = world.CreateJoint(mouseJointDef) as b2MouseJoint;
}
}
private function onMouseUp(e:MouseEvent):void{
if(mouseJoint){
world.DestroyJoint(mouseJoint);
mouseJoint = null;
}
}
private function getBodyAtMouse(includeStatic:Boolean = false):b2Body{
var mouseXWorldPhys:Number = mouseX/pixelsPerMeter;
var mouseYWorldPhys:Number = mouseY/pixelsPerMeter;
mousePVec.Set(mouseXWorldPhys,mouseYWorldPhys);
// 利用当前鼠标向量建立一个很小的b2AABB
var aabb:b2AABB = new b2AABB();
aabb.lowerBound.Set(mouseXWorldPhys-0.001,mouseYWorldPhys-0.001);
aabb.upperBound.Set(mouseXWorldPhys+0.001,mouseYWorldPhys+0.001);
var body:b2Body = null;
var fixture:b2Fixture;
function GetBodyCallBack(fixture:b2Fixture):Boolean{
var shape:b2Shape = fixture.GetShape();
if(fixture.GetBody().GetType() != b2Body.b2_staticBody || includeStatic){
var inside:Boolean = shape.TestPoint(fixture.GetBody().GetTransform(),mousePVec);
if(inside){
body = fixture.GetBody();
return false;
}
}
return true;
}
// 在World中查找与鼠标向量定义的Shape相重叠的Shape
world.QueryAABB(GetBodyCallBack,aabb);
return body;
}
private function onEnterframe(e:Event):void{
world.Step(timeStep,iterations,iterations);
world.ClearForces();
world.DrawDebugData();
if(mouseJoint){
var xpos:Number = mouseX/pixelsPerMeter;
var ypos:Number = mouseY/pixelsPerMeter;
var v2:b2Vec2 = new b2Vec2(xpos,ypos);
mouseJoint.SetTarget(v2);
}
}
}
}
[/code]
