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，将高斯模糊的图当作上层元素的背景，利用背景定位使其只显示一部分，然后把这个高斯模糊的窗口放置在高清图的上层，背景图片的位置与下面的图片位置一致，这样看起来就像一张高清的图片打上了马赛克一样。讲起来不是很清楚，大家可以看一下代码。
基础版本
HTML
#css_box {
position: relative;
width: 100%;
height: 500px;
background: url(‘https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1567844929804&di=75928af77a3db7ff54cd4eab49361bc0&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fblog%2F201307%2F19%2F20130719082039_k2NHG.jpeg’) no-repeat;
}
#css_target {
position: absolute;
left: 0px;
top: 0px;
width: 200px;
height: 200px;
background: inherit;
filter: blur(10px);
/* 继承父元素的background属性 */
}
var bar = document.getElementById(“css_box”);
var target = document.getElementById(“css_target”);
startDrag(bar, target, function(x, y) {
target.style.backgroundPosition = (-1 * x) + “px ” + (-1 * y) + “px”;
});
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JS (当作JS文件引入)
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) {
maxX = parseInt(getCss(bar, “width”)) – parseInt(getCss(target, “width”));
maxY = parseInt(getCss(bar, “height”)) – parseInt(getCss(target, “height”));
var resX = 0,
resY = 0;
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”);
}
target.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;
if ((parseInt(params.left) + disX) > maxX) {
resX = maxX;
} else if ((parseInt(params.left) + disX) < 0) {
resX = 0;
} else {
resX = parseInt(params.left) + disX;
}
if ((parseInt(params.top) + disY) > maxY) {
resY = maxY;
} else if ((parseInt(params.top) + disY) < 0) {
resY = 0;
} else {
resY = parseInt(params.top) + disY;
}
target.style.left = resX + ‘px’
target.style.top = resY + ‘px’
if (typeof callback == “function”) {
callback(resX, resY);
}
if (event.preventDefault) {
event.preventDefault();
}
return false;
}
}
};
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兼容移动端优化版本
HTML
#css_box {
position: relative;
touch-action: none;
width: 100%;
height: 500px;
background: url(‘https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1567844929804&di=75928af77a3db7ff54cd4eab49361bc0&imgtype=0&src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fblog%2F201307%2F19%2F20130719082039_k2NHG.jpeg’) no-repeat;
background-size: contain;
}
#css_target {
position: absolute;
left: 0px;
top: 0px;
background: inherit;
filter: blur(10px);
touch-action: none;
/* 继承父元素的background属性 */
}
mosaic Demo
传送门
X: 0 px Y: 0 px
$(document).ready(function() {
var bar = document.getElementById(“css_box”);
var target = document.getElementById(“css_target”);
var p_img = document.getElementById(“position_img”);
// 兼容分辨率
bar.style.height = (parseInt(getCss(bar, “width”)) * 636 / 900) + ‘px’;
target.style.backgroundSize = parseInt(getCss(bar, “width”)) + ‘px ‘ + (parseInt(getCss(bar, “width”)) * 636 / 900) + ‘px’;
startDrag(bar, target, function(x, y) {
target.style.backgroundPosition = (-1 * x) + “px ” + (-1 * y) + “px”;
p_img.innerText = “X: ” + target.style.left + ” Y: ” + target.style.top;
});
})
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JS (当作JS文件引入)
// 拖拽
var startDrag = function(bar, target, callback) {
var getCss = function(o, key) {
return o.currentStyle ? o.currentStyle[key] : document.defaultView.getComputedStyle(o, false)[key];
};
var down = function(event) {
// 兼容分辨率
bar.style.height = (parseInt(getCss(bar, “width”)) * 636 / 900) + ‘px’;
target.style.backgroundSize = parseInt(getCss(bar, “width”)) + ‘px ‘ + (parseInt(getCss(bar, “width”)) * 636 / 900) + ‘px’;
params.flag = true;
if (!event) {
event = window.event;
bar.onselectstart = function() {
return false;
}
}
var e = event;
params.currentX = e.clientX || e.changedTouches[0].clientX;
params.currentY = e.clientY || e.changedTouches[0].clientY;
};
var up = function() {
params.flag = false;
if (getCss(target, “left”) !== “auto”) {
params.left = getCss(target, “left”);
}
if (getCss(target, “top”) !== “auto”) {
params.top = getCss(target, “top”);
}
};
var move = function(event) {
var e = event ? event : window.event;
if (params.flag) {
var nowX = e.clientX || e.changedTouches[0].clientX,
nowY = e.clientY || e.changedTouches[0].clientY;
var disX = nowX – params.currentX,
disY = nowY – params.currentY;
if ((parseInt(params.left) + disX) > maxX) {
resX = maxX;
} else if ((parseInt(params.left) + disX) < 0) {
resX = 0;
} else {
resX = parseInt(params.left) + disX;
}
if ((parseInt(params.top) + disY) > maxY) {
resY = maxY;
} else if ((parseInt(params.top) + disY) < 0) {
resY = 0;
} else {
resY = parseInt(params.top) + disY;
}
target.style.left = resX + ‘px’
target.style.top = resY + ‘px’
if (typeof callback == “function”) {
callback(resX, resY);
}
if (event.preventDefault) {
event.preventDefault();
}
return false;
}
}
var resX = 0,
resY = 0;
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”);
}
if ((navigator.userAgent.match(/(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i))) {
console.log(“mobile”);
target.style.width = ‘100px’;
target.style.height = ‘100px’;
maxX = parseInt(getCss(bar, “width”)) – parseInt(getCss(target, “width”));
maxY = parseInt(getCss(bar, “height”)) – parseInt(getCss(target, “height”));
target.ontouchstart = down
document.ontouchend = up
document.ontouchmove = move
} else {
console.log(“pc”);
target.style.width = ‘150px’;
target.style.height = ‘150px’;
maxX = parseInt(getCss(bar, “width”)) – parseInt(getCss(target, “width”));
maxY = parseInt(getCss(bar, “height”)) – parseInt(getCss(target, “height”));
target.onmousedown = down
document.onmouseup = up
document.onmousemove = move
}
};
复制代码以上就是局部模糊的实现方法。可以直接套用。将JS部分当作文件引入。否则要把初始化函数放在函数声明的后面。
最后可查看实际效果：demo演示地址
借鉴于张鑫旭大神