【9RIA—ladeng6666】—【Box2D系列教程 10】创建圆角刚体

9RIA-ladeng6666

转载：9RIA游戏开发者社区（天地会）
作者：ladeng6666（拉登大叔）
作者博客：http://www.ladeng6666.com/blog/


【Box2D系列教程-导航帖】—拉登大叔出品（总贴）



上次我们讨论了如何创建一个多边形刚体，终于摆脱了简单的矩形和圆形，又上了一个台阶。

这不，刚学会走，有人就想跑了。天地会的xiaopang125同学前两天问我如何创建一个圆角刚体，我用创建多边形刚体教程里的组合法实现了这个效果：
点击舞台任意位置，创建圆角刚体

[Actionscript3] 纯文本查看 复制代码

private function createRoundBody(posX:Number,posY:Number,width:Number,height:Number,radius:Number):void
{
    //1.创建刚体需求b2BodyDef
    var bodyRequest:b2BodyDef = new b2BodyDef();
    bodyRequest.position.Set(posX / 30, posY / 30);//记得米和像素的转换关系
    //2.Box2D世界工厂更具需求创建createBody()生产刚体
    body=world.CreateBody(bodyRequest);
    //3.创建敢提形状需求b2ShapeDef的子类

    /*    详细说明我们的需求
创建多个b2Shape需求
然后b2Body刚体工厂根据需求createShape生产形状
    */
    //把像素转换成Box2D里的米
    var b2Width:Number = width / 2 / 30;
    var b2height:Number = height / 2 / 30;
    var b2Radius:Number = radius / 2 / 30;
    var offsetX:Number = b2Width - b2Radius;
    var offsetY:Number = b2height - b2Radius;

    //------------------------------------
    //     首先创建两个矩形，我分别把它们高和宽减去了radius，留给圆角用，你可以注释掉下面创建圆角的代码，看看效果
    var shapeRequest:b2PolygonDef = new b2PolygonDef();

    shapeRequest.density = 3;
    shapeRequest.friction = 0.3;
    shapeRequest.restitution = 0.2;
    //创建两个矩形
    shapeRequest.SetAsOrientedBox(b2Width, b2height - b2Radius);
    body.CreateShape(shapeRequest);
    shapeRequest.SetAsOrientedBox(b2Width - b2Radius, b2height);
    body.CreateShape(shapeRequest);
    //------------------------------------
    //       然后，分别在四个角上创建四个圆形，实现圆角效果
    var circleRequest:b2CircleDef = new b2CircleDef();
    circleRequest.density = 3;
    circleRequest.friction = 0.3;
    circleRequest.restitution = 0.3;
    circleRequest.radius = b2Radius;

    circleRequest.localPosition = new b2Vec2(-offsetX, -offsetY);
    body.CreateShape(circleRequest);
    circleRequest.localPosition = new b2Vec2(offsetX, -offsetY);
    body.CreateShape(circleRequest);
    circleRequest.localPosition = new b2Vec2(-offsetX, offsetY);
    body.CreateShape(circleRequest);
    circleRequest.localPosition = new b2Vec2(offsetX, offsetY);
    body.CreateShape(circleRequest);

    body.SetMassFromShapes();

}

代码除了下面创建圆角刚体的函数之外，与创建多边形刚体里的基本一致。下面的代码我已经做了详细的注释，就不再赘述了。

圆角效果实现了，接下来给我自己以及大家留个家庭作业，请参考"刚体的上衣——b2BodyDef.userData"一节，给圆形刚体穿上上衣。

下载：
OK 2012-07-03 创建圆角刚体.rar (254.7 KB, 下载次数: 0)

2018-2-5 16:28 上传

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2.1a版

[Actionscript3] 纯文本查看 复制代码

package {

        import Box2D.Collision.Shapes.b2CircleShape;
        import Box2D.Collision.Shapes.b2PolygonShape;
        import Box2D.Common.Math.b2Vec2;
        import Box2D.Dynamics.b2Body;
        import Box2D.Dynamics.b2BodyDef;
        import Box2D.Dynamics.b2DebugDraw;
        import Box2D.Dynamics.b2FixtureDef;
        import Box2D.Dynamics.b2World;

        import flash.display.Sprite;
        import flash.events.Event;
        import flash.events.MouseEvent;

        public class YuanJiaoJuXingGangTi extends Sprite {
                private var world:b2World;
                private var body:b2Body;
                private const WORLDSCALE:int = 30;

                public function YuanJiaoJuXingGangTi() {
                        createWorld();
                        createGround();
                        createDebug();
                        addEventListener(Event.ENTER_FRAME, loop);
                        stage.addEventListener(MouseEvent.MOUSE_DOWN, onStageMouseDown);
                }

                private function createWorld():void {
                        var gravity:b2Vec2 = new b2Vec2(0, 10);
                        var doSleep:Boolean = true;
                        world = new b2World(gravity, doSleep);
                }

                private function createGround():void {
                        var polygonShape:b2PolygonShape = new b2PolygonShape();
                        polygonShape.SetAsBox(stage.stageWidth / WORLDSCALE, 0.5 / WORLDSCALE);
                        var fixtureDef:b2FixtureDef = new b2FixtureDef();
                        fixtureDef.density = 0;
                        fixtureDef.friction = 0.3;
                        fixtureDef.restitution = 0.2;
                        fixtureDef.shape = polygonShape;
                        var bodyDef:b2BodyDef = new b2BodyDef();
                        bodyDef.type = b2Body.b2_staticBody;
                        bodyDef.position.Set(stage.stageWidth / 2 / WORLDSCALE, stage.stageHeight / WORLDSCALE);
                        body = world.CreateBody(bodyDef);
                        body.CreateFixture(fixtureDef);
                }

                private function createDebug():void {
                        var debugSprite:Sprite = new Sprite();
                        addChild(debugSprite);
                        var debugDraw:b2DebugDraw = new b2DebugDraw();
                        debugDraw.SetSprite(debugSprite);
                        debugDraw.SetDrawScale(30);
                        debugDraw.SetAlpha(0.5);
                        debugDraw.SetLineThickness(1);
                        debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit);
                        world.SetDebugDraw(debugDraw);
                }

                private function createRoundPolygon(posX:Number, posY:Number, w:Number, h:Number, r:Number):void {
                        var offsetX:Number = w / WORLDSCALE - r / WORLDSCALE;
                        var offsetY:Number = h / WORLDSCALE - r / WORLDSCALE;
                        var bodyDef:b2BodyDef = new b2BodyDef();
                        bodyDef.type = b2Body.b2_dynamicBody;
                        bodyDef.position.Set(posX / WORLDSCALE, posY / WORLDSCALE);
                        body = world.CreateBody(bodyDef);
                        var circleShape:b2CircleShape = new b2CircleShape();
                        circleShape.SetRadius(r / WORLDSCALE);
                        var polygonShape:b2PolygonShape = new b2PolygonShape();
                        var fixtureDef:b2FixtureDef = new b2FixtureDef();
                        fixtureDef.density = 3;
                        fixtureDef.friction = 0.3;
                        fixtureDef.restitution = 0.3;
                        fixtureDef.shape = polygonShape;
                        polygonShape.SetAsOrientedBox(w / WORLDSCALE, h / WORLDSCALE - r / WORLDSCALE, new b2Vec2());
                        body.CreateFixture(fixtureDef);
                        polygonShape.SetAsOrientedBox(w / WORLDSCALE - r / WORLDSCALE, h / WORLDSCALE, new b2Vec2());
                        body.CreateFixture(fixtureDef);
                        fixtureDef.shape = circleShape;
                        circleShape.SetLocalPosition(new b2Vec2(-offsetX, -offsetY));
                        body.CreateFixture(fixtureDef);
                        circleShape.SetLocalPosition(new b2Vec2(offsetX, -offsetY));
                        body.CreateFixture(fixtureDef);
                        circleShape.SetLocalPosition(new b2Vec2(-offsetX, offsetY));
                        body.CreateFixture(fixtureDef);
                        circleShape.SetLocalPosition(new b2Vec2(offsetX, offsetY));
                        body.CreateFixture(fixtureDef);
                }

                private function onStageMouseDown(e:MouseEvent):void {
                        createRoundPolygon(mouseX, mouseY, 40, 20, 10);
                }

                private function loop(e:Event):void {
                        world.Step(1 / 30, 10, 10);
                        world.ClearForces();
                        world.DrawDebugData();
                }
        }
}