JQuery 自定义CircleAnimation，Animate方法学习笔记

在此贴出一些学习成果，希望能对学习JQuery的其他同学有所帮助，同时也记录下自己的学习情况。
看了一些JQuery的官方教程，已经有点心潮澎湃了，就决定自己尝试着写一些东西出来。我看到了很多很绚的动画效果，然后决定自己也尝试一下，我决定要写一个圆周运动的动画效果，下面贴出js代码

var CircleAnimation = function (center_left, center_top, id, clockwise, duration) { 
return new CircleAnimation.fn.init(center_left, center_top, id, clockwise, duration); 
}; 
CircleAnimation.fn = CircleAnimation.prototype = { 
item: {}, 
init: 
function (center_left, center_top, id, clockwise, duration) { 
this.item = $("#" + id + ""); 
if (!this.item[0]) 
return; 
currentPoint = { 
x: this.item.css("left") == "auto" ? 0 : String(this.item.css("left")).replace("px", "") - center_left, 
y: this.item.css("top") == "auto" ? 0 : String(this.item.css("top")).replace("px", "") - center_top 
}; 
center_left = center_left; 
center_top = center_top; 
if (currentPoint.x == 0 && currentPoint.y == 0) 
return; 
r = Math.pow(Math.pow(currentPoint.x, 2) + Math.pow(currentPoint.y, 2), 0.5); 
var flag = false; 
var caculateMiniAngle = function (angle) { 
//caculate the minimum angle diff, if the distance between 2 points less than 1px, we think this 2 ponits angle should be the minimum angle diff 
if (Math.sin(angle / 2) * 2 * r > 1) { 
return caculateMiniAngle(angle / 2); 
} 
else { 
return angle; 
} 
} 
miniAngle = caculateMiniAngle(Math.PI / 4); 
//store data to dom element 
this.item.data("currentPoint", currentPoint); 
this.item.data("center_left", center_left); 
this.item.data("center_top", center_top); 
this.item.data("r", r); 
this.item.data("clockwise", clockwise); 
this.item.data("miniAngle", miniAngle); 
this.item.data("duration", duration); 
//this.item.data("startX", this.startX); 
}, 
start: 
function () { 
var element; 
if (this.id) 
element = $("#" + this.id.toString()); 
else 
element = this.item; 
element.animate({ left: 1, top: 1 }, { 
duration: element.data( 
"duration"), 
step: CircleAnimation.fn.caculateNextPoint 
}); 
}, 
caculateNextPoint: 
function () { 
var el; 
el = $( 
"#" + this.id.toString()); 
var sin = el.data("currentPoint").y / el.data("r"); 
var angle = Math.asin(sin); 
if (el.data("currentPoint").x < 0) 
angle = Math.PI - angle; 
//caculate the angle diff between current point angle and next point angle 
var anglediff = el.data("miniAngle"); 
if (el.data("duration") != undefined) 
anglediff = 2 * Math.PI * 13 / el.data( 
"duration"); 
if (el.data("clockwise")) 
angle = angle - anglediff; 
else 
angle = angle + anglediff; 
var y = el.data("r") * Math.sin(angle); 
var x = el.data("r") * Math.cos(angle); 
var fx = arguments[1]; 
//set duration big enough then circle animation never stop 
fx.options.duration = ( 
new Date).getTime() - fx.startTime + 10000; 
if (fx.prop == "top") 
fx.now = y + el.data( 
"center_top"); 
if (fx.prop == "left") 
fx.now = x + el.data( 
"center_left"); 
el.data( 
"currentPoint", { x: x, y: y }); 
}, 
stop: 
function () { 
this.item.queue("fx", []); 
this.item.stop(); 
} 
}; 
CircleAnimation.fn.init.prototype = CircleAnimation.fn;