hammer.js实现背景图手势缩放调整位置

<!DOCTYPE html>
<html>
<head>
<script>
function getxy(e){
    var a=new Array()
    var t=e.offsetTop;
    var l=e.offsetLeft;
    var w=e.offsetWidth;
    var h=e.offsetHeight;
    while(e=e.offsetParent){
        t+=e.offsetTop;
        l+=e.offsetLeft;
    }
    a[0]=w;a[1]=h;
    a[2]=l;a[3]=t;
    return a;
}
</script>
    <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1, maximum-scale=1">
    <link rel="stylesheet" href="assets/style.css">
    <title>Hammer.js</title>

    <style>
		*, *:after, *:before {
			box-sizing: border-box;
			-moz-box-sizing: border-box;
		}

		html, body {
			margin: 0;
			padding: 0;
			height: 100%;
			min-height: 100%;
			background: #eee;
			font: 13px/1.5em 'Open Sans', Helvetica, Arial, sans-serif;
		}

		a {
			color: #4986e7;
		}

		.bg1, .green { background: #42d692; }
		.bg2, .blue { background: #4986e7; }
		.bg3, .red { background: #d06b64; }
		.bg4, .purple { background: #cd74e6; }
		.bg5, .azure { background: #9fe1e7; }

		body {
			margin: 20px;
		}

		pre {
			background: #fff;
			padding: 20px;
			margin-bottom: 20px;
		}

		.container {
			max-width: 900px;
			margin: 0 auto;
		}

		.clear { clear: both; }

        html, body {
            overflow: hidden;
            margin: 0;
        }

        body {
            -webkit-perspective: 500;
            -moz-perspective: 500;
            perspective: 500;
        }

        .animate {
            -webkit-transition: all .3s;
            -moz-transition: all .3s;
            transition: all .3s;
        }

        #hit {
            padding: 10px;
        }

        #log {
            position: absolute;
            padding: 10px;
        }

		.bg2{
			width:15em; height:40em; margin:0 auto;
			/*background-image:url(1.jpg);*/
			position:fixed;
			z-index:-2;
			background-repeat:no-repeat;
		}
    </style>
</head>
<body>
<div class="bg2" id="bg2">

</div>

<script src="hammer.js"></script>
<script>
    var reqAnimationFrame = (function () {
        return window[Hammer.prefixed(window, 'requestAnimationFrame')] || function (callback) {
            window.setTimeout(callback, 1000 / 60);
        };
    })();

	var bg = document.getElementById("bg2");
	var xy = getxy(bg);
	var bgP = {
				x:0,y:0,dx:0,dy:0,
				s:1,ls:1,bdw:xy[0],bdh:xy[1]
			};

    var mc = new Hammer.Manager(bg);

	function imgLoaded(){
		bgP.bgw = this.width;
		bgP.bgh = this.height;

		if(bgP.bgw / bgP.bgh > bgP.bdw / bgP.bdh)
			bgP.useW = false;
		else
			bgP.useW = true;

		this.style.display = 'none';

		bg.style.backgroundImage = 'url('+this.src+')';
		bg.style.backgroundSize = bgP.useW? (bgP.bgw+'px auto') : ('auto '+bgP.bgh+'px');

		mc.add(new Hammer.Pan({ threshold: 0, pointers: 0 }));

		mc.add(new Hammer.Rotate({ threshold: 0 })).recognizeWith(mc.get('pan'));
		mc.add(new Hammer.Pinch({ threshold: 0 })).recognizeWith([mc.get('pan'), mc.get('rotate')]);

		mc.on("panstart panmove", onPan);
		//mc.on("rotatestart rotatemove", onRotate);
		mc.on("pinchstart pinchmove", onPinch);

		mc.on("hammer.input", function(ev) {
			if(ev.isFinal) {
				bgP.dx = 0;
				bgP.dy = 0;
				bgP.ls = 1;
			}
		});
	}

    function onPan(ev) {
        bgP.x += ev.deltaX - bgP.dx;
		bgP.y += ev.deltaY - bgP.dy;

		console.log('x='+(ev.deltaX - bgP.dx)+', y='+(ev.deltaY - bgP.dy));

		bgP.dx = ev.deltaX;
		bgP.dy = ev.deltaY;

		if(bgP.x>0) bgP.x = 0;
		if(bgP.y>0) bgP.y = 0;

		if(bgP.x+bgP.bgw*bgP.s<bgP.bdw)
			bgP.x = bgP.bdw - bgP.bgw*bgP.s;

		if(bgP.y+bgP.bgh*bgP.s<bgP.bdh)
			bgP.y = bgP.bdh - bgP.bgh*bgP.s;

		var pos = bgP.x+'px '+bgP.y+'px';
		bg.style.backgroundPosition = pos;
    }

    var initScale = 1;
    function onPinch(ev) {
        if(ev.type == 'pinchstart') {
            initScale = transform.scale || 1;
        }
		var add = ev.scale - bgP.ls;
		bgP.s += add;
		bgP.ls = ev.scale;

		if(bgP.useW){
			var w = (bgP.bgw*bgP.s);
			if(w<bgP.bdw)
			{
				bgP.s = bgP.bdw/bgP.bgw;
				w = (bgP.bgw*bgP.s);
			}
			bg.style.backgroundSize = w +'px auto';
		}else{
			var h = (bgP.bgh*bgP.s);
			if(h<bgP.bdh)
			{
				bgP.s = bgP.bdh/bgP.bgh;
				h = (bgP.bgh*bgP.s);
			}
			bg.style.backgroundSize = 'auto '+h +'px';
		}
    }

	function bgStart(src){
		var img = document.createElement('img');
		img.src = src;
		img.style.opacity = '0.01';
		img.onload = imgLoaded;
	}
	bgStart('1.jpg');
</script>

</body>
</html>