高级对象与角色控制技术解析

# 高级对象与角色控制技术解析 ## 1. 全方位发射弹丸案例分析 在这个案例中，我们可以通过拖动鼠标让 Button Fairy 在舞台上飞行。同时，其“魔杖”会围绕精灵旋转并指向鼠标光标，点击鼠标左键就能向各个方向发射星星，星星碰到舞台边界会被移除。这个案例展示了以下关键游戏设计技术： - 如何让一个对象围绕另一个对象旋转 - 如何全方位发射弹丸 - 如何使用组合技术，通过一个 `GameObject` 类创建所有游戏对象 ### 1.1 代码实现 以下是实现该功能的完整应用类代码： ```actionscript package { import flash.display.DisplayObject; import flash.display.Sprite; import flash.events.Event; import flash.events.MouseEvent; import flash.ui.Mouse; [SWF(width="550", height="400", backgroundColor="#FFFFFF", frameRate="60")] public class ButtonFairy extends Sprite { //Embed the images [Embed(source="../images/fairy.png")] private var FairyImage:Class; [Embed(source="../images/wand.png")] private var WandImage:Class; [Embed(source="../images/star.png")] private var StarImage:Class; //Private properties private const EASING:Number = 0.1; private var _fairyImage:DisplayObject = new FairyImage(); private var _wandImage:DisplayObject = new WandImage(); //Create the fairy and wand game objects //(The images will be centered by the GameObject class) private var _fairy:GameObject = new GameObject(_fairyImage); private var _wand:GameObject = new GameObject(_wandImage); //A variable to store the angle between //the mouse and the center of the fairy private var _angle:Number; //An array to store the stars private var _stars:Array = new Array(); public function ButtonFairy() { //Add the fairy and the wand to the stage stage.addChild(_fairy); stage.addChild(_wand); //Hide the mouse Mouse.hide(); //Add the event listeners stage.addEventListener (Event.ENTER_FRAME, enterFrameHandler); stage.addEventListener (MouseEvent.MOUSE_DOWN, mouseDownHandler); } private function enterFrameHandler(event:Event):void { //Find the angle between the center of the //fairy and the mouse _angle = Math.atan2 ( _fairy.y - stage.mouseY, _fairy.x - stage.mouseX ); //Move the wand around the fairy var radius:int = -50; _wand.x = _fairy.x + (radius * Math.cos(_angle)); _wand.y = _fairy.y + (radius * Math.sin(_angle)); //Figure out the distance between the //mouse and the center of the fairy var vx:Number = stage.mouseX - _fairy.x; var vy:Number = stage.mouseY - _fairy.y; var distance:Number = Math.sqrt(vx * vx + vy * vy); //Move the fairy if it's more than 1 pixel away from the mouse if (distance >= 1) { _fairy.x += vx * EASING; _fairy.y += vy * EASING; } //Move the stars for(var i:int = 0; i < _stars.length; i++) { var star:GameObject = _stars[i]; star.x += star.vx; star.y += star.vy; //check the star's stage boundaries if (star.y < 0 || star.x < 0 || star.x > stage.stageWidth || star.y > stage.stageHeight) { //Remove the star from the stage stage.removeChild(star); star = null; //Remove the star from the _stars array _stars.splice(i,1); //Reduce the loop counter //by one to compensate //for the removed star i--; } } } private function mouseDownHandler(event:MouseEvent):void { //Create a star and add it to the stage var starImage:DisplayObject = new StarImage(); var star:Game ```