本文部分素材来自QQ部落（http://bl.qq.com）,仅作研究学习之用，如有侵权，请与本站联系。 SWF效果如下： 本实例用的是二次贝塞尔曲线，详情见代码。 逻辑类如下： [codesyntax lang=”php”]
package com.sqstudio.study.qqbl.archer
{
import com.sqstudio.study.util.Bezier;
import flash.display.Sprite;
import flash.display.Stage;
import flash.events.Event;
import flash.geom.Point;
/**
*QQ部落箭塔之弓箭飞行
* @author Nestor
* @website sqstudio.com
*
*/
public class ArcherStudy extends Sprite
{
private var arrow:UI_Arrow;
private var drawPathSp:Sprite;
private var startPoint:Point;
private var endPoint:Point;
private var controlPoint:Point;
private var tower:UI_Tower;
private var monster:UI_Monster;
private var steps:uint;
private var crtStep:int;
public function ArcherStudy()
{
//塔
tower = new UI_Tower();
tower.shooterLeft.stop();
tower.shooterRight.stop();
this.addChild(tower);
tower.x = 100;
tower.y = 150;
//怪
monster = new UI_Monster();
this.addChild(monster);
monster.x = 400;
monster.y = 300;
//箭头
this.arrow = new UI_Arrow();
this.addChild(arrow);
//初始化数据
startPoint = new Point(tower.x,tower.y-30);
controlPoint = new Point(monster.x-200,tower.y-130);
endPoint = new Point(monster.x,monster.y-20);
steps = Bezier.init(startPoint,controlPoint,endPoint,8);
this.crtStep = 0;//当前步
this.addEventListener(Event.ENTER_FRAME,loopEfHandler);
//路径绘制SP
drawData();
}
/**
*循环帧频函数
* @param e
*
*/
private function loopEfHandler(e:Event):void
{
var tmpArr:Array = Bezier.getAnchorPoint(crtStep);
arrow.x = tmpArr[0];
arrow.y = tmpArr[1];
arrow.rotation = tmpArr[2];
this.crtStep++;
if(crtStep>steps){
crtStep=0;
if(Math.random()>0.5){
tower.shooterLeft.gotoAndPlay(2);
}else{
tower.shooterRight.gotoAndPlay(2);
}
}
}
/**
*绘制路线
*
*/
private function drawData():void{
this.drawPathSp = new Sprite();
this.addChild(drawPathSp);
drawPathSp.graphics.lineStyle(1,0,0.5);
drawPathSp.graphics.moveTo(startPoint.x, startPoint.y);
drawPathSp.graphics.curveTo(controlPoint.x, controlPoint.y,endPoint.x, endPoint.y);
drawPathSp.graphics.endFill();
drawP(startPoint);
drawP(endPoint);
drawP(controlPoint);
drawPathSp.graphics.moveTo(startPoint.x,startPoint.y);
drawPathSp.graphics.lineTo(endPoint.x,endPoint.y);
drawPathSp.graphics.lineTo(controlPoint.x,controlPoint.y);
drawPathSp.graphics.lineTo(startPoint.x,startPoint.y);
}
/**
*生成顶点
* @param p
* @param type
* @return
*
*/
public function drawP(p:Point):Sprite{
var sp:Sprite = new Sprite();
this.addChild(sp);
sp.graphics.beginFill(0xffffff*Math.random());
sp.graphics.drawCircle(0,0,4);
sp.graphics.endFill();
sp.x = p.x;
sp.y = p.y;
return sp;
}
}
}
[/codesyntax] 实例中，怪物的位置是固定，贝塞尔曲线的控制点也是手动调整的，这两个因素在实际游戏中是不一样的，尤其是控制的点，也应该有计算公式，具体的算法就留待你来扩展了，具体表现效果可以到QQ部落游戏中去体验（声明，我不是托儿，QQ部落也是抄袭国外一款塔防游戏的Kingdom Rush） 工具类（来自网上，略作整理）： [codesyntax lang=”php”]
package com.sqstudio.study.util
{
import flash.geom.Point;
public class Bezier
{
// ===================================== 属性
// 对外变量
private static var p0:Point;// 起点
private static var p1:Point;// 控制点
private static var p2:Point;// 终点
private static var step:uint;// 分割份数
// 辅助变量
private static var ax:int;
private static var ay:int;
private static var bx:int;
private static var by:int;
private static var A:Number;
private static var B:Number;
private static var C:Number;
private static var total_length:Number;// 长度
// ===================================== 方法
// 速度函数
private static function s (t:Number):Number
{
return Math.sqrt(A * t * t + B * t + C);
}
// 长度函数
private static function L (t:Number):Number
{
var temp1:Number = Math.sqrt(C + t * (B + A * t));
var temp2:Number = (2 * A * t * temp1 + B *(temp1 - Math.sqrt(C)));
var temp3:Number = Math.log(B + 2 * Math.sqrt(A) * Math.sqrt(C));
var temp4:Number = Math.log(B + 2 * A * t + 2 * Math.sqrt(A) * temp1);
var temp5:Number = 2 * Math.sqrt(A) * temp2;
var temp6:Number = (B * B - 4 * A * C) * (temp3 - temp4);
return (temp5 + temp6) / (8 * Math.pow(A, 1.5));
}
// 长度函数反函数，使用牛顿切线法求解
private static function InvertL (t:Number, l:Number):Number
{
var t1:Number = t;
var t2:Number;
do
{
t2 = t1 - (L(t1) - l)/s(t1);
if (Math.abs(t1-t2) < 0.000001) break;
t1 = t2;
}while(true);
return t2;
}
// ===================================== 封装
// 返回所需总步数
/**
*获得所需步数
* @param $p0
* @param $p1
* @param $p2
* @param $speed
* @return
*
*/
public static function init ($p0:Point, $p1:Point, $p2:Point, $speed:Number):uint
{
p0 = $p0;
p1 = $p1;
p2 = $p2;
//step = 30;
ax = p0.x - 2 * p1.x + p2.x;
ay = p0.y - 2 * p1.y + p2.y;
bx = 2 * p1.x - 2 * p0.x;
by = 2 * p1.y - 2 * p0.y;
A = 4*(ax * ax + ay * ay);
B = 4*(ax * bx + ay * by);
C = bx * bx + by * by;
// 计算长度
total_length = L(1);
// 计算步数
step = Math.floor(total_length / $speed);
if (total_length % $speed > $speed / 2)step ++;
return step;
}
// 根据指定nIndex位置获取锚点：返回坐标和角度
public static function getAnchorPoint (nIndex:Number):Array
{
if (nIndex >= 0 && nIndex <= step)
{
var t:Number = nIndex/step;
// 如果按照线行增长，此时对应的曲线长度
var l:Number = t*total_length;
// 根据L函数的反函数，求得l对应的t值
t = InvertL(t, l);
// 根据贝塞尔曲线函数，求得取得此时的x,y坐标
var xx:Number = (1 - t) * (1 - t) * p0.x + 2 * (1 - t) * t * p1.x + t * t * p2.x;
var yy:Number = (1 - t) * (1 - t) * p0.y + 2 * (1 - t) * t * p1.y + t * t * p2.y;
// 获取切线
var Q0:Point = new Point((1 - t) * p0.x + t * p1.x, (1 - t) * p0.y + t * p1.y);
var Q1:Point = new Point((1 - t) * p1.x + t * p2.x, (1 - t) * p1.y + t * p2.y);
// 计算角度
var dx:Number = Q1.x - Q0.x;
var dy:Number = Q1.y - Q0.y;
var radians:Number = Math.atan2(dy, dx);
var degrees:Number = radians * 180 / Math.PI;
return new Array(xx, yy, degrees);
}
else
{
return [];
}
}
}
}
[/codesyntax] 延伸阅读：http://zh.wikipedia.org/zh-cn/%E8%B4%9D%E5%A1%9E%E5%B0%94%E6%9B%B2%E7%BA%BF