【9RIA—ladeng6666】—【Box2D系列教程 16】多边形刚体贴图

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）


在前面的刚体的上衣教程中，我们学会了简单的刚体贴图，确实非常简单，只需要根据b2Body刚体的坐标和角度实时更新userData的坐标和角度就可以了。那么多边形刚体贴图呢？

放心啦，没你想象的那么复杂，和简单刚体的贴图方法是一样一样的，重点是如何绘制和多边形刚体一样的图形，很幸运，我们在用drawPath自由绘制图形中已经学会了，结合运行时创建多边形刚体，我们可以轻松给多边形刚体啦(如果你还不熟练，强烈建议你好好看看这两篇教程)。效果如下：



完整的代码和注释如下：

[Actionscript3] 纯文本查看 复制代码

package
{
	import Box2D.Collision.b2AABB;
	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 Box2DSeparator.b2Separator;
	import flash.display.Bitmap;
	import flash.display.BitmapData;
	import flash.display.DisplayObject;
	import flash.geom.Matrix;
 
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
	import flash.geom.Point;
	import flash.display.GraphicsPathCommand;
 
	/**
	 * [url]http://www.ladeng6666.com[/url]
	 * @author ladeng6666
	 */
	public class MainWithSeparator extends Sprite
	{
		private const segmentLength:Number = 20;
 
		private var world:b2World;
		//绘制图形的画布
		private var spriteCanvas:Sprite;
		private var spriteCommand:Vector.<int> = new Vector.<int>();
		private var spriteData:Vector.<Number> = new Vector.<Number>();
		//绘制图像的纹理
		private var woodBmd:BitmapData = new Wood();
 
		private var prePoint:Point = new Point();
		private var curPoint:Point = new Point();
 
		private var verticesList:Vector.<b2Vec2> = new Vector.<b2Vec2>();
 
		private var isDrawing:Boolean = false;
		public function MainWithSeparator()
		{
			//创建box2D世界
			world = LDEasyBox2D.createWorld();
			//创建box2D调试图
			addChild(LDEasyBox2D.createDebug(world));
			//创建地面
			LDEasyBox2D.createWrapWall(world,stage);
 
			spriteCanvas = new Sprite();
			addChild(spriteCanvas);
			//侦听事件
			addEventListener(Event.ENTER_FRAME, loop);
			stage.addEventListener(MouseEvent.MOUSE_DOWN, onStageMouseDown);
			stage.addEventListener(MouseEvent.MOUSE_UP, onStageMouseUp);
			stage.addEventListener(MouseEvent.MOUSE_MOVE, onStageMouseMove);
		}
 
		private function onStageMouseMove(e:MouseEvent):void
		{
			//如果鼠标没有按下，isDrawing为false，跳出
			if(!isDrawing) return;
			spriteCanvas.graphics.lineTo(mouseX, mouseY);
			//记录鼠标坐标为当前curPoint，并计算curPoint与上一个点prePoint的距离
			curPoint = new Point(mouseX, mouseY);
			var distance:Number = Point.distance(prePoint, curPoint);
			//当前后两个点的距离大于线段距离时，添加顶点
			if (distance >= segmentLength) {
				//记录顶点到verticesList数组中
				verticesList.push(new b2Vec2(mouseX / 30, mouseY / 30));
				prePoint = curPoint.clone();
				//存储绘制命令和绘制顶点
				spriteCommand.push(GraphicsPathCommand.LINE_TO);
				spriteData.push(mouseX);
				spriteData.push(mouseY);
			}
		}
 
		private function onStageMouseUp(e:MouseEvent):void
		{
			spriteCommand.push(GraphicsPathCommand.LINE_TO);
			spriteData.push(spriteData[0]);
			spriteData.push(spriteData[1]);
			//鼠标弹起后，停止绘制
			isDrawing = false;
			//画布里的内容
			spriteCanvas.graphics.clear();
			//在鼠标位置随机创建一个多边形刚体
			var polygonBody:b2Body=createPolygon();
			if (polygonBody != null) {
				createUseData(polygonBody, spriteCommand, spriteData);
			}
			//清空存储命令和顶点的数组
			spriteCommand = new Vector.<int>();
			spriteData = new Vector.<Number>();
			//清空存储顶点的Vector数组
			verticesList = new Vector.<b2Vec2>();
		}
		/**
		 * 鼠标按下事件侦听
		 * @param	e
		 */
		private function onStageMouseDown(e:MouseEvent):void
		{
			//鼠标按下后，开始绘制
			isDrawing = true;
			//设置线条样式
			spriteCanvas.graphics.lineStyle(2);
			spriteCanvas.graphics.moveTo(mouseX, mouseY);
			//存储绘制命令和绘制顶点
			spriteCommand.push(GraphicsPathCommand.MOVE_TO);
			spriteData.push(mouseX);
			spriteData.push(mouseY);
			//定义鼠标点为起点
			curPoint = new Point(mouseX, mouseY);
			prePoint = curPoint.clone();
 
			verticesList.push(new b2Vec2(mouseX / 30, mouseY / 30));
		}
		/**
		 * 刷新屏幕
		 * @param	e
		 */
		private function loop(e:Event):void
		{
			world.Step(1 / 30, 10, 10);
			world.ClearForces();
			world.DrawDebugData();
 
			for (var body:b2Body = world.GetBodyList(); body; body=body.GetNext()) {
				if (body.GetUserData() != null) {
					//根据刚体的坐标个角度，更新绑定的userData
					body.GetUserData().x = body.GetPosition().x * 30;
					body.GetUserData().y = body.GetPosition().y * 30;
					body.GetUserData().rotation = body.GetAngle() * 180 / Math.PI;
				}
			}
		}
		/**
		 * 创建多边形刚体
		 * @return
		 */
		private function createPolygon():b2Body
		{
			//1.创建刚体需求b2BodyDef
			var bodyRequest:b2BodyDef = new b2BodyDef();
			bodyRequest.type = b2Body.b2_dynamicBody;
			bodyRequest.position.Set(0 , 0);//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
			var body:b2Body=world.CreateBody(bodyRequest);
			//3.创建敢提形状需求b2ShapeDef的子类
				//创建矩形刚体形状需求
			var fixtureRequest:b2FixtureDef = new b2FixtureDef();
			fixtureRequest.density = 3;
			fixtureRequest.friction = 0.3;
			fixtureRequest.restitution = 0.2;
			//创建一个Separator对象
			var separator:b2Separator = new b2Separator();
			//验证顶点是否符合创建多边形的标准
			var validate:int = separator.Validate(verticesList);
			//如果是顶点因非顺时针不符标准，则反转数组中的顶点顺序
			if (validate == 2) {
				verticesList.reverse();
			}else if (validate != 0) {
				//如果不符合多边形标准，跳出
				return null;
			}
			//将顶点分解成多个凸多边形，组合成复杂的多边形
			separator.Separate(body, fixtureRequest, verticesList);
 
			return body;
		}
		/**
		 * 根据存储的路径、顶点绘制多边形图形，并绑定到刚体中
		 * @param	body 要添加贴图的刚体
		 * @param	commandVector 存储绘图命令的刚体
		 * @param	posVector 存储绘图顶点的刚体
		 */
		private function createUseData(body:b2Body, commandVector:Vector.<int>, posVector:Vector.<Number>):void {
			//创建一个空白的画布
			var canvas:Sprite = new Sprite();
			canvas.graphics.clear();
			canvas.graphics.lineStyle(3, 0x4D370B);
			//利用存储的命令和顶点绘制并填充图形
			canvas.graphics.beginBitmapFill(woodBmd);
			canvas.graphics.drawPath(commandVector, posVector);
			canvas.graphics.endFill();
			addChild(canvas);
			//把画布绑定到刚体中
			body.SetUserData(canvas);
		}
	}
 
}