【9RIA—ladeng6666】—【Box2D系列教程 10】创建圆角刚体
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
attach://785.swf
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：
2.1a版
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();
}
}
}
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