css-sprite
为纪念美国现代舞舞蹈家玛莎·葛兰姆诞辰，Google Doodle推出了一款极其炫酷的LOGO，整个LOGO使用CSS Sprite技术，利用一个初始图片和一张画满各个动作的拼接图片，实现了动画，而非传统的GIF动画图像。
效果
CSS Sprite简介
CSS Sprites(css精灵)，是一种网页图片应用处理方式。它允许你将一个页面涉及到的所有零星图片都包含到一张大图中去，这样一来，当访问该页面时，载入的图片就不会像以前那样一幅一幅地慢慢显示出来了。
限制：不高于200KB的单张图片
整合处理图片的目的是减少请求次数，如果每一张图片都向服务器发送请求，即影响服务器负载也影响页面性能。
CSS Sprite原理
CSS Sprites的原理就是把网页中用到的小图标、图片类集中整合到一张图片中。
再利用CSS中的背景属性
- background-image
- background-repeat
- background-position
当需要显示指定图片时，定位到图片相应位置即可
Google粘土动画
实现步骤：
1、准备素材，设计动画的每一帧图片并整合成一张图片
2、监听点击事件执行动画
3、根据延迟时间设置图片背景位置以显示下一帧图片
素材
HTML
<div>
<div style="display:flex;align-items:flex-end;">
<div style="width:135px;height:156px;background:url(/images/css-sprite/blockheads.png) 0 0;" id="blockheads"></div>
<div style="width:65px;height:102px;background:url(/images/css-sprite/prickle.png) 0 0;" id="prickle"></div>
<div style="width:67px;height:144px;background:url(/images/css-sprite/goo.png) 0 0;" id="goo"></div>
<div style="width:98px;height:156px;background:url(/images/css-sprite/gumby.png) 0 0;" id="gumby"></div>
<div style="width:75px;height:108px;background:url(/images/css-sprite/pokey.png) 0 0;" id="pokey"></div>
</div>
</div>
JS
<script>
class Sprite {
constructor(opt) {
this.element = document.getElementById(opt.element);
this.url = opt.url;
this.delay = 1000 / (opt.speed || 20);
this.defaultBackground = this.element.style.background;
this.defalutUrl = this.element.style.backgroundImage;
this.step = 0;
this.width = this.element.clientWidth;
this.height = this.element.clientHeight;
let img = new Image();
img.onload = () => {
this.cols = parseInt(img.width / this.width);
this.rows = parseInt(img.height / this.height);
this.frames = this.cols * this.rows;
this.element.onclick = () => {
this.play();
};
};
img.src = this.url;
}
play() {
if (this.playing) {
return;
}
this.playing = true;
this.next();
}
next() {
this.step++;
if (this.step > this.frames) {
this.stop();
return;
}
let x = this.step % this.cols;
let y = parseInt(this.step / this.rows);
if (this.step % this.rows > 0) {
y++;
}
var position = "-" + (x - 1) * this.width + "px -" + (y - 1) * this.height + "px";
this.element.style.background = "url(" + this.url + ") " + position;
setTimeout(() => {
this.next();
}, this.delay);
}
stop() {
this.step = 0;
this.playing = false;
this.element.style.background = this.defaultBackground;
}
}
window.addEventListener('load', () => {
new Sprite({
element: 'blockheads',
url:'/images/css-sprite/blockheads.png'
});
new Sprite({
element: 'prickle',
url:'/images/css-sprite/prickle.png'
});
new Sprite({
element: 'goo',
url:'/images/css-sprite/goo.png'
});
new Sprite({
element: 'gumby',
url:'/images/css-sprite/gumby.png'
});
new Sprite({
element: 'pokey',
url:'/images/css-sprite/pokey.png'
});
});
</script>
Google舞蹈者
实现步骤：
1、准备素材，收集舞蹈者每一个动作集成到一张图片
2、初始化每一个动作的位置
3、定时动态创建div元素设置背景位置和元素位置
素材
HTML
<div id="graham-logo" style="position:relative;height:150px;"></div>
JS
(function () {
window.google={};
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],
e = d.length,
f, g, h, i, j = -1,
c = document.getElementById("graham-logo"),
l = function () {
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if (c && a[0]) {
var b = document.createElement("div");
b.id = "graham-logo" + f;
b.style.position = "absolute";
b.style.left = a[0] + "px";
b.style.top = a[1] + "px";
b.style.width = a[2] + "px";
b.style.height = a[3] + "px";
b.style.background = "url(/images/css-sprite/graham-sprite.png) no-repeat " + -g + "px " + -h + "px";
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m = function () {
google.doodle.a = !1;
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j != -1 && (window.clearTimeout(j), j = -1);
c.innerHTML = "";
j = window.setTimeout(l, 83)
};
c.addEventListener ? c.addEventListener("click", m, !1) : c.attachEvent("onclick", m);
if (!google.doodle.a) {
google.doodle.a = !0;
var n = document.createElement("img");
n.addEventListener ? n.addEventListener("load", m, !1) : n.attachEvent("onload", m);
n.src = "/images/css-sprite/graham-sprite.png"
}
})();
总结
希望大家可以通过本文的Google动画实现了解到一些CSS Sprite技术，CSS Sprite是前端优化的一部分，合理的利用好可以提高网页的性能，也可以丰富网页内容。
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