css3+js：图片的局部模糊

css3+js: 局部高斯模糊的实现

前两篇文介绍了css3的过滤器filter用来实现图片的高斯模糊效果，还有js拖拽的功能。
要实现局部模糊就要把两者结合起来，计算位移就可以了。

实现原理

原理其实很简单，就是两张图的叠加。底部一张清晰的图，上面一个高斯模糊过的图，局部显示与下面的图片无缝重合，这样看起来就行下面的图片部分模糊了一样。

代码

<style type="text/css">
#box{
    position:relative;
    width:500px;
    height:500px;
    background: url('xxx.jpg') no-repeat;
}
#target{
    position:absolute; 
    left:0px; 
    top:0px; 
    width:100px;
    height:100px;
    background: inherit; //继承父元素的background属性
}

</style>
<div id="#box">
    <div id="#target">

    </div>
</div>
var bar = document.getElementById("bar");
var target = document.getElementById("target");
startDrag(target,target, function(x,y){
    eleDrag.style.backgroundPosition = (-1 * x) + "px " + (-1 * y) + "px"; 
});

为实现局部模糊的回调
var eleDrag = document.getElementById("box");
if (eleDrag) {
    startDrag(eleDrag, eleDrag, function(x, y) {
        eleDrag.style.backgroundPosition = (-1 * x) + "px " + (-1 * y) + "px";    
    });
}*/
var getCss = function(o,key){
    return o.currentStyle? o.currentStyle[key] : document.defaultView.getComputedStyle(o,false)[key];
};
// 拖拽
var startDrag = function(bar, target, callback){
    var params = {
        left: 0,
        top: 0,
        currentX: 0,
        currentY: 0,
        flag: false
    };
    if(getCss(target, "left") !== "auto"){
        params.left = getCss(target, "left");
    }
    if(getCss(target, "top") !== "auto"){
        params.top = getCss(target, "top");
    }
    bar.onmousedown = function(event){
        params.flag = true;
        if(!event){
            event = window.event;
            bar.onselectstart = function(){
                return false;
            }
        }
        var e = event;
        params.currentX = e.clientX;
        params.currentY = e.clientY;
    };
    document.onmouseup = function(){
        params.flag = false;
        if(getCss(target, "left") !== "auto"){
            params.left = getCss(target, "left");
        }
        if(getCss(target, "top") !== "auto"){
            params.top = getCss(target, "top");
        }
    };
    document.onmousemove = function(event){
        var e = event ? event: window.event;
        if(params.flag){
            var nowX = e.clientX, nowY = e.clientY;
            var disX = nowX - params.currentX, disY = nowY - params.currentY;
            target.style.left = parseInt(params.left) + disX + "px";
            target.style.top = parseInt(params.top) + disY + "px";

            if (typeof callback == "function") {
                callback((parseInt(params.left) || 0) + disX, (parseInt(params.top) || 0) + disY);
            }
            if (event.preventDefault) {
                event.preventDefault();
            }
            return false;
        }
    }
};

以上就是局部模糊的实现方法。可以直接套用。

借鉴于张鑫旭大神