Flash Box2D 入门

 

从今天开始，学习Box2D, 由于Flash熟悉一点，所以选用Flash平台。

Box2D源库地址：http://box2dflash.sourceforge.net/

今天实现目标，创建一个四周都是墙壁的环境，里面放两个方块。如图：

首先了解几个要用的类：b2AABB，b2World，b2Body，b2BodyDef

b2AABB：An axis aligned bounding box.（官方文档的解释是），大概意思是一个轴边界对齐的盒子。

b2World：The world class manages all physics entities, dynamic simulation, and asynchronous queries.
中文大概意思是：管理所有物理实体、动态模拟和异步的的一个环境。

b2Body：A rigid body（刚体）

b2BodyDef：A body definition holds all the data needed to construct a rigid body. You can safely re-use body definitions
中文大概意思是：定义一个刚体需要的数据，构建了一种刚体。你可以安全地重用的刚体的定义。

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.b2World;import flash.display.Sprite;import flash.events.Event;import General.Input;/** * ... * @author Terry.Xu */public class Main extends Sprite{private var mainSprite:Sprite;private var aabb:b2AABB;private var world:b2World;private var body:b2Body;public var m_physScale:Number = 30;//真实世界与模拟世界的比例public function Main(){mainSprite = new Sprite();addChild(mainSprite);//创建画板aabb = new b2AABB();//设置范围aabb.lowerBound.Set(-100, -100);aabb.upperBound.Set(100, 100);var vec2:b2Vec2 = new b2Vec2(0, 10.0);//构建一个重力的向量var doSleep:Boolean = true;//这个参数设置为true时，物体不运动或没有碰撞时，物体可以处于sleep状态。world = new b2World(vec2, doSleep);var shape:b2PolygonShape = new b2PolygonShape();//实例一个多边形shape.SetAsBox(20 / m_physScale, 30 / m_physScale);var bodyDef:b2BodyDef = new b2BodyDef(); //创建方块1bodyDef.position.Set(100 / m_physScale, 100 / m_physScale);bodyDef.type = b2Body.b2_dynamicBody;//定义的物体是可移动的body = world.CreateBody(bodyDef);body.CreateFixture2(shape, 1);//注意，这个方法的第二个参数是物体的密度，这个参数大于0后。//当着力点不在物体中心时，物体会自己旋转//创建方块2bodyDef.position.Set(150 / m_physScale, 100 / m_physScale);bodyDef.type = b2Body.b2_dynamicBody;body = world.CreateBody(bodyDef);body.CreateFixture2(shape,10);//创建挡板//leftbodyDef.position.Set(-5 / m_physScale, 0 / m_physScale);bodyDef.type = b2Body.b2_staticBody;shape.SetAsBox(10 / m_physScale,400 / m_physScale);body = world.CreateBody(bodyDef);body.CreateFixture2(shape);//rightbodyDef.position.Set(555 / m_physScale, 0 / m_physScale);bodyDef.type = b2Body.b2_staticBody;body = world.CreateBody(bodyDef);body.CreateFixture2(shape);//topbodyDef.position.Set(0 / m_physScale, -5 / m_physScale);bodyDef.type = b2Body.b2_staticBody;shape.SetAsBox(550 / m_physScale, 10 / m_physScale);body = world.CreateBody(bodyDef);body.CreateFixture2(shape);//bottombodyDef.position.Set(0 / m_physScale, 405 / m_physScale);bodyDef.type = b2Body.b2_staticBody;body = world.CreateBody(bodyDef);body.CreateFixture2(shape);//Debug Drawvar dbgDraw:b2DebugDraw = new b2DebugDraw();dbgDraw.SetDrawScale(m_physScale);dbgDraw.SetSprite(mainSprite);dbgDraw.SetLineThickness(1);dbgDraw.SetFlags(b2DebugDraw.e_shapeBit);dbgDraw.SetFillAlpha(.3);world.SetDebugDraw(dbgDraw);world.SetWarmStarting(true);this.addEventListener(Event.ENTER_FRAME, onUpdate);}private function onUpdate(e:Event):void{mainSprite.graphics.clear();world.Step(1 / 30, 10, 10);world.ClearForces();world.DrawDebugData();}}}

这个例子只是简单的演示Box2D在Flash的基本做法，下篇将会引入鼠标控制和与真实显示对象接合。