Flex高级动画教程中所讲的避开行为

package vector.steering

{

??? public class SteeredVehicle extends Vehicle

??? {

??????? private var _maxForce:Number = 1;????? //旋转力

??????? private var _steeringForce:Vector2D;?? //作为叠加后的转向合力

???????

??????? public function SteeredVehicle()

??????? {

??????????? _steeringForce = new Vector2D();

??????????? super();

??????? }

???????

??????? public function set maxForce(value:Number):void{

??????????? _maxForce = value;

??????? }

???????

??????? public function get maxForce():Number{

??????????? return _maxForce;

??????? }

???????

??????? /**

??????? ?* 主要控制旋转力

??????? ?*/

??????? override public function update():void{

??????????? _steeringForce.truncate(_maxForce);

??????????? _steeringForce = _steeringForce.divide(_mass);

??????????? _velocity = _velocity.add(_steeringForce);

??????????? _steeringForce = new Vector2D();

??????????? super.update();

??????? }

???????

??????? /**

??????? ?* 寻找行为 把机车移动到指定点

??????? ?*/

??????? public function seek(target:Vector2D):void{

??????????? var desiredVelocity:Vector2D = target.substract(_position);

??????????? desiredVelocity.normalize();

??????????? desiredVelocity = desiredVelocity.multiply(_maxSpeed);

??????????? var force:Vector2D = desiredVelocity.substract(_velocity);

??????????? _steeringForce = _steeringForce.add(force);

???????????

??????? }

???????

??????? /**

??????? ?* 避开行为

??????? ?*/

??????? public function flee(target:Vector2D):void{

??????????? var desiredVelocity: Vector2D = target.substract(_position);

??????????? desiredVelocity.normalize();

??????????? desiredVelocity = desiredVelocity.multiply(_maxSpeed);

??????????? var force: Vector2D = desiredVelocity.substract(_velocity);

??????????? _steeringForce = _steeringForce.substract(force);

??????? }

??? }

}

?

--测试类

package vector.chapter1

{

??? import flash.display.Sprite;

??? import flash.display.StageAlign;

??? import flash.display.StageScaleMode;

??? import flash.events.Event;

???

??? import vector.steering.SteeredVehicle;

??? import vector.steering.Vector2D;

??? import vector.steering.Vehicle;

???

??? public class FleeTest extends Sprite

??? {

??????? private var _vehicle:SteeredVehicle;

???????

???????

??????? public function FleeTest(){

??????????? stage.align = StageAlign.TOP_LEFT;

??????????? stage.scaleMode = StageScaleMode.NO_SCALE;

???????????

??????????? _vehicle = new SteeredVehicle();

??????????? _vehicle.position = new Vector2D(200,200);

??????????? _vehicle.edgeBehavior = Vehicle.BOUNCE;

??????????? addChild(_vehicle);

???????????

??????????? addEventListener(Event.ENTER_FRAME,onEnterFrame);

??????? }

???????

??????? private function onEnterFrame(event:Event):void

??????? {

??????????? _vehicle.flee(new Vector2D(mouseX,mouseY));

??????????? _vehicle.update();

??????? }

??? }

}

?

避开行为与寻找行为彻底相反。实际上，除了代码最后一行用相减代替了相加以外，其它都一样。