dom-drag 今天学了学js里面的拖拉

很久不写代码了,一直不是做管理,不是招聘面试,再就是写方案
技术都有些生了,今天正好安排了一个protal的定制任务下去,自己也顺手看了看.
有一个做好的库,叫dom-drag.js,封装得不错,打开看了一下例子,刚开始有几个问题一直没有理解,花了一个多小时,总算都搞明白了,把想明白的地方写下来:


<html>
<head>
<title> - cropper - </title>
<style type="text/css">
<!--
#pbox {
		width:300px; height:300px;
		overflow:hidden;
	}
.opacity{filter: alpha(opacity=60)}
-->
</style>
<script language="javascript" src="dom-drag.js"></script>
<script language="javascript">
	var oThang, oHandle, reportBox, iReportCount = 0;

	window.onload = function() {
		if (document.all || document.getElementById)
		{
			oThang = document.all ? document.all["thang"] : document.getElementById("thang")
			oHandle = document.all ? document.all["handle"] : document.getElementById("handle")
			oReport = document.all ? document.all["report"] : document.getElementById("report")

			Drag.init(oHandle, oThang, -250, 150, -250, 150);

			// report stuff
			oThang.onDrag = function(x, y) { reportDrag("", x, y); }
		}

		function reportDrag(who, x, y) {
			oReport.value = who + "" + " X = " + (x + 250) + " Y = " + (y + 250) + " W = 100 H = 100"
		}

		oThang.onDrag(-250, -250);
	}
</script>
</head>

<body>

<div style="width:300px; height:300px; overflow:hidden; top:20px; left:20px;">
	<img src="snare_pic_large-300.jpg" />
	<div id="thang" style="position:absolute; left:-250px; top:-250px;">sdfs
		<img class="opacity" style="position:absolute; left:0px; top:0px;" src="selection2.gif" />
		<img id="handle" style="position:absolute; left:250px; top:250px; width:100px; height:100px;" src="x.gif" />
	</div>
</div>

<input type="text" id="report" style="width:300px;" />

</body>
</html>


1)在cropper.html中的最外层的div上加了overflow:hidden,如果去掉的话,就对不齐了,这是因为,最外层的div是相对的,相对于body的,而里面的div thang是绝对定位的,会参考上一个绝对定位的父对象,也就是body,而不是最外层的div,所以,如果加上overflow:hidden以后,div thang就会参考最外层的div,但是具体为什么我不是很清楚,只是知道就是这样一个效果,针对绝对定位的div有效,如果把最外的div改成绝对定位的话,就不需要overflow:hidden了
2)cropper.html是起到了个蒙板的效果,中间有一个100*100的透明窗,可以看到后面的图,这个透明窗是selection2.gif提供的,开始,我以为这个文件也就是100*100的,而其位置是绝对定位到0,0,这样的话,会相对其上一个绝对定位的父对象,也就是div thang,而div thang却定位到-250,-250,这样的话,不就是看不见了吗?想了十分钟才解决,原来selection2.gif居然是600*600的,这真是一个不是问题的问题,一下子就解决了.
记下来免得以后忘记了,dom-drag封装得还是不错的,只是后面的几个参数
/**************************************************
 * dom-drag.js
 * 09.25.2001
 * www.youngpup.net
 **************************************************
 * 10.28.2001 - fixed minor bug where events
 * sometimes fired off the handle, not the root.
 **************************************************/

var Drag = {

	obj : null,

	init : function(o, oRoot, minX, maxX, minY, maxY, bSwapHorzRef, bSwapVertRef, fXMapper, fYMapper)
	{
		o.onmousedown	= Drag.start;

		o.hmode			= bSwapHorzRef ? false : true ;
		o.vmode			= bSwapVertRef ? false : true ;

		o.root = oRoot && oRoot != null ? oRoot : o ;

		if (o.hmode  && isNaN(parseInt(o.root.style.left  ))) o.root.style.left   = "0px";
		if (o.vmode  && isNaN(parseInt(o.root.style.top   ))) o.root.style.top    = "0px";
		if (!o.hmode && isNaN(parseInt(o.root.style.right ))) o.root.style.right  = "0px";
		if (!o.vmode && isNaN(parseInt(o.root.style.bottom))) o.root.style.bottom = "0px";

		o.minX	= typeof minX != 'undefined' ? minX : null;
		o.minY	= typeof minY != 'undefined' ? minY : null;
		o.maxX	= typeof maxX != 'undefined' ? maxX : null;
		o.maxY	= typeof maxY != 'undefined' ? maxY : null;

		o.xMapper = fXMapper ? fXMapper : null;
		o.yMapper = fYMapper ? fYMapper : null;

		o.root.onDragStart	= new Function();
		o.root.onDragEnd	= new Function();
		o.root.onDrag		= new Function();
	},

	start : function(e)
	{
		var o = Drag.obj = this;
		e = Drag.fixE(e);
		var y = parseInt(o.vmode ? o.root.style.top  : o.root.style.bottom);
		var x = parseInt(o.hmode ? o.root.style.left : o.root.style.right );
		o.root.onDragStart(x, y);

		o.lastMouseX	= e.clientX;
		o.lastMouseY	= e.clientY;

		if (o.hmode) {
			if (o.minX != null)	o.minMouseX	= e.clientX - x + o.minX;
			if (o.maxX != null)	o.maxMouseX	= o.minMouseX + o.maxX - o.minX;
		} else {
			if (o.minX != null) o.maxMouseX = -o.minX + e.clientX + x;
			if (o.maxX != null) o.minMouseX = -o.maxX + e.clientX + x;
		}

		if (o.vmode) {
			if (o.minY != null)	o.minMouseY	= e.clientY - y + o.minY;
			if (o.maxY != null)	o.maxMouseY	= o.minMouseY + o.maxY - o.minY;
		} else {
			if (o.minY != null) o.maxMouseY = -o.minY + e.clientY + y;
			if (o.maxY != null) o.minMouseY = -o.maxY + e.clientY + y;
		}

		document.onmousemove	= Drag.drag;
		document.onmouseup		= Drag.end;

		return false;
	},

	drag : function(e)
	{
		e = Drag.fixE(e);
		var o = Drag.obj;

		var ey	= e.clientY;
		var ex	= e.clientX;
		var y = parseInt(o.vmode ? o.root.style.top  : o.root.style.bottom);
		var x = parseInt(o.hmode ? o.root.style.left : o.root.style.right );
		var nx, ny;

		if (o.minX != null) ex = o.hmode ? Math.max(ex, o.minMouseX) : Math.min(ex, o.maxMouseX);
		if (o.maxX != null) ex = o.hmode ? Math.min(ex, o.maxMouseX) : Math.max(ex, o.minMouseX);
		if (o.minY != null) ey = o.vmode ? Math.max(ey, o.minMouseY) : Math.min(ey, o.maxMouseY);
		if (o.maxY != null) ey = o.vmode ? Math.min(ey, o.maxMouseY) : Math.max(ey, o.minMouseY);

		nx = x + ((ex - o.lastMouseX) * (o.hmode ? 1 : -1));
		ny = y + ((ey - o.lastMouseY) * (o.vmode ? 1 : -1));

		if (o.xMapper)		nx = o.xMapper(y)
		else if (o.yMapper)	ny = o.yMapper(x)

		Drag.obj.root.style[o.hmode ? "left" : "right"] = nx + "px";
		Drag.obj.root.style[o.vmode ? "top" : "bottom"] = ny + "px";
		Drag.obj.lastMouseX	= ex;
		Drag.obj.lastMouseY	= ey;

		Drag.obj.root.onDrag(nx, ny);
		return false;
	},

	end : function()
	{
		document.onmousemove = null;
		document.onmouseup   = null;
		Drag.obj.root.onDragEnd(	parseInt(Drag.obj.root.style[Drag.obj.hmode ? "left" : "right"]), 
									parseInt(Drag.obj.root.style[Drag.obj.vmode ? "top" : "bottom"]));
		Drag.obj = null;
	},

	fixE : function(e)
	{
		if (typeof e == 'undefined') e = window.event;
		if (typeof e.layerX == 'undefined') e.layerX = e.offsetX;
		if (typeof e.layerY == 'undefined') e.layerY = e.offsetY;
		return e;
	}
};

bSwapHorzRef, bSwapVertRef, fXMapper, fYMapper,读了一下程序,是只能垂直移动和水平移动,而fXMapper和fYMapper是做坐标转换的,觉得应该是传两个function进去的.

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