构建随机运动的效果

//求平面坐标系中两点间的距离
function getdistance(x1, y1, x2, y2) {
var a, b;
a=x2-x1;
b=y2-y1;
return (Math.sqrt(a*a+b*b));
}

//运动距离、范围、速率的设置

MovieClip.prototype.chance = function() {
width = 400;
height = 250;
//mc运动范围的设置
var c, d;
this.x = this._x;
this.y = this._y;
//速率、目标位置的随机设置
this.speed = Math.random()*4+2;
this.targx = Math.random()*width;
this.targy = Math.random()*height;
c = _root.getdistance(this.x, this.y, this.targx, this.targy);
d = this.speed/c;
//mc运动时x、y坐标的增量
this.diffx = (this.targx-this.x)*d;
this.diffy = (this.targy-this.y)*d;
};

//mc运动及停止时间的设置

MovieClip.prototype.move = function() {
//运动的判定
if (_root.getdistance(this.x, this.y, this.targx, this.targy)>this.speed) {
this.x += this.diffx;
this.y += this.diffy;
} else {
this.x = this.targx;
this.y = this.targy;
//停止时间的判定
if (!this.t) {
this.t = getTimer();
}
if (getTimer()-this.t>1000) {
this.chance();
//停止时间大于1秒，调用chance()进行下一次的随机运动
this.t = 0;
}
}
this._x = this.x;
this._y = this.y;
};

//button instance name :Add
Add.onRelease=function(){
n++;
_root.mc.duplicateMovieClip("mc" add n ,n);
trace(n);
}

Delete Clip button code:
//button instance name :Delete
Delete.onRelease=function(){
if (n>0) {
_root["mc"add n].gotoAndPlay(2);
n -= 1;
trace(n);
}
}