解析3D标签云，其实很简单

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　　最近开始用canvas搞3D了，搞得也是简单的东西，就是球体转圈。做出来后，突然想起以前看过的3D标签云，在以前觉得真心狂拽酷炫叼啊，当时也确实不知道怎么在平面上模拟3D，所以也就没去搞了。现在刚好用了canvas搞3D，也发现，好像3D标签云也差不多，然后就写了一下。

　　具体怎么做呢，先说一下原理，3D标签云就是做一个球面，然后再球面上取均匀分布的点，把点坐标赋给标签，再根据抽象出来的Z轴大小来改变标签的字体大小，透明度，做出立体感觉，然后球体就做好了。关键代码就下面这几句：

function innit(){
            for(var i=0;i<tagEle.length;i++){
                var a , b;
                var k = -1+(2*(i+1)-1)/tagEle.length;
                var a = Math.acos(k);
                var b = a*Math.sqrt(tagEle.length*Math.PI);
                // var a = Math.random()*2*Math.PI;
                // var b = Math.random()*2*Math.PI;
                var x = RADIUS * Math.sin(a) * Math.cos(b);
                var y = RADIUS * Math.sin(a) * Math.sin(b); 
                var z = RADIUS * Math.cos(a);
                var t = new tag(tagEle[i] , x , y , z);
                tagEle[i].style.color = "rgb("+parseInt(Math.random()*255)+","+parseInt(Math.random()*255)+","+parseInt(Math.random()*255)+")";
                tags.push(t);
                t.move();
            }
        }

上面的代码是用于生成球面上的点的x,y,z轴的坐标。用到的就是简单的球面方程：已知半径r和球心，一般为了方便，我们都以坐标轴原点为球心，有下面三个方程

　x=r*sinθ*cosΦ   y=r*sinθ*sinΦ   z=r*cosθ;

也就是说，我们可以对θ和Φ取随机数，来获得圆上的随机点坐标。但仅此还不够，因为如果要做3D标签云，一个很重要点的就是平均分布。如果单纯的取随机坐标，会导致一些标签重叠，相对来说就没那么美观了。所以我们引入第二个公式：

θ = arccos( ((2*num)-1)/all - 1);

Φ = θ*sqrt(all * π);

num是当前第几个点，all则是点的总数。这个公式的是我在别人的代码里找到的，我也不懂原理。不过确实好用。

有了上面两个公式以后，我们就可以获得球面上所需要的平均分布的点。然后再对每个标签进行操作：

var scale = fallLength/(fallLength-this.z);
var alpha = (this.z+RADIUS)/(2*RADIUS);
this.ele.style.fontSize = 15 * scale + "px";
this.ele.style.opacity = alpha+0.5;
this.ele.style.filter = "alpha(opacity = "+(alpha+0.5)*100+")";
this.ele.style.zIndex = parseInt(scale*100);
this.ele.style.left = this.x + CX - this.ele.offsetWidth/2 +"px";
this.ele.style.top = this.y + CY - this.ele.offsetHeight/2 +"px";
fallLength是焦距，也就是一个常量，scale和alpha都是要根据z轴来调整的比例。后面的属性操作就比较简单了，调整一下字体大小，透明度，以及元素位置，球体就做出来了，效果如下（忽略字的内容，乱写的）：

球体做出来了，是时候让其动起来了。这时就引入第三个公式了，矩阵旋转算法:

还可以直接戳 计算机图形学3D变换；

然后，我们就可以写出两个函数，一个是绕X轴旋转，一个是绕Y轴旋转。

function rotateX(){
            var cos = Math.cos(angleX);
            var sin = Math.sin(angleX);
            tags.forEach(function(){
                var y1 = this.y * cos - this.z * sin;
                var z1 = this.z * cos + this.y * sin;
                this.y = y1;
                this.z = z1;
            })
            
        }

        function rotateY(){
            var cos = Math.cos(angleY);
            var sin = Math.sin(angleY);
            tags.forEach(function(){
                var x1 = this.x * cos - this.z * sin;
                var z1 = this.z * cos + this.x * sin;
                this.x = x1;
                this.z = z1;
            })
        }

然后就可以通过控制angleX和angleY两个角度的值来控制标签云的旋转方向以及旋转速度，角度的正负值控制旋转方向，大小控制旋转速度。

接下来就可以用鼠标事件来控制了：

if("addEventListener" in window){
            paper.addEventListener("mousemove" , function(event){
                var x = event.clientX - EX - CX;
                var y = event.clientY - EY - CY;
                // angleY = -x* (Math.sqrt(Math.pow(x , 2) + Math.pow(y , 2)) > RADIUS/4 ? 0.0002 : 0.0001);
                // angleX = -y* (Math.sqrt(Math.pow(x , 2) + Math.pow(y , 2)) > RADIUS/4 ? 0.0002 : 0.0001);
                angleY = x*0.0001;
                angleX = y*0.0001;
            });
        }
        else {
            paper.attachEvent("onmousemove" , function(event){
                var x = event.clientX - EX - CX;
                var y = event.clientY - EY - CY;
                angleY = x*0.0001;
                angleX = y*0.0001;
            });
        }

当这个也写好后，3D标签云就算完工了，完成效果就直接看DEMO吧：3D标签云；

下面贴出标签云的所有代码，其实都可以通过控制台看代码，不过还是贴一下吧：（本人技术不是很好，代码写的不好请见谅）

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
    <style>
        .tagBall{
            width: 800px;
            height: 800px;
            margin:50px auto;
            position: relative;
        }
        .tag{
            display: block;
            position: absolute;
            left: 0px;
            top: 0px;
            color: #000;
            text-decoration: none;
            font-size: 15px;
            font-family: "微软雅黑";
            font-weight: bold;
        }
        .tag:hover{border:1px solid #666;}
    </style>
    <title>3D标签</title>
</head>
<body>
    <div class="tagBall">
        <a class="tag" target="_blank" href="http://2.axescanvas.sinaapp.com/LoveDemo/secondLove.html">某某某</a>
        <a class="tag" target="_blank" href="http://2.axescanvas.sinaapp.com/LoveDemo/secondLove.html">我喜欢你</a>
        <a class="tag" target="_blank" href="http://2.axescanvas.sinaapp.com/LoveDemo/secondLove.html">某某某</a>
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    </div>
    <script>
        var tagEle = "querySelectorAll" in document ? document.querySelectorAll(".tag") : getClass("tag"),
            paper = "querySelectorAll" in document ? document.querySelector(".tagBall") : getClass("tagBall")[0];
            RADIUS =300,
            fallLength = 500,
            tags=[],
            angleX = Math.PI/500,
            angleY = Math.PI/500,
            CX = paper.offsetWidth/2,
            CY = paper.offsetHeight/2,
            EX = paper.offsetLeft + document.body.scrollLeft + document.documentElement.scrollLeft,
            EY = paper.offsetTop + document.body.scrollTop + document.documentElement.scrollTop;

        function getClass(className){
            var ele = document.getElementsByTagName("*");
            var classEle = [];
            for(var i=0;i<ele.length;i++){
                var cn = ele[i].className;
                if(cn === className){
                    classEle.push(ele[i]);
                }
            }
            return classEle;
        }

        function innit(){
            for(var i=0;i<tagEle.length;i++){
                var a , b;
                var k = (2*(i+1)-1)/tagEle.length - 1;
                var a = Math.acos(k);
                var b = a*Math.sqrt(tagEle.length*Math.PI);
                // var a = Math.random()*2*Math.PI;
                // var b = Math.random()*2*Math.PI;
                var x = RADIUS * Math.sin(a) * Math.cos(b);
                var y = RADIUS * Math.sin(a) * Math.sin(b); 
                var z = RADIUS * Math.cos(a);
                var t = new tag(tagEle[i] , x , y , z);
                tagEle[i].style.color = "rgb("+parseInt(Math.random()*255)+","+parseInt(Math.random()*255)+","+parseInt(Math.random()*255)+")";
                tags.push(t);
                t.move();
            }
        }

        Array.prototype.forEach = function(callback){
            for(var i=0;i<this.length;i++){
                callback.call(this[i]);
            }
        }

        function animate(){
            setInterval(function(){
                rotateX();
                rotateY();
                tags.forEach(function(){
                    this.move();
                })
            } , 17)
        }

        if("addEventListener" in window){
            paper.addEventListener("mousemove" , function(event){
                var x = event.clientX - EX - CX;
                var y = event.clientY - EY - CY;
                // angleY = -x* (Math.sqrt(Math.pow(x , 2) + Math.pow(y , 2)) > RADIUS/4 ? 0.0002 : 0.0001);
                // angleX = -y* (Math.sqrt(Math.pow(x , 2) + Math.pow(y , 2)) > RADIUS/4 ? 0.0002 : 0.0001);
                angleY = x*0.0001;
                angleX = y*0.0001;
            });
        }
        else {
            paper.attachEvent("onmousemove" , function(event){
                var x = event.clientX - EX - CX;
                var y = event.clientY - EY - CY;
                angleY = x*0.0001;
                angleX = y*0.0001;
            });
        }
        
        function rotateX(){
            var cos = Math.cos(angleX);
            var sin = Math.sin(angleX);
            tags.forEach(function(){
                var y1 = this.y * cos - this.z * sin;
                var z1 = this.z * cos + this.y * sin;
                this.y = y1;
                this.z = z1;
            })
            
        }

        function rotateY(){
            var cos = Math.cos(angleY);
            var sin = Math.sin(angleY);
            tags.forEach(function(){
                var x1 = this.x * cos - this.z * sin;
                var z1 = this.z * cos + this.x * sin;
                this.x = x1;
                this.z = z1;
            })
        }

        var tag = function(ele , x , y , z){
            this.ele = ele;
            this.x = x;
            this.y = y;
            this.z = z;
        }

        tag.prototype = {
            move:function(){
                var scale = fallLength/(fallLength-this.z);
                var alpha = (this.z+RADIUS)/(2*RADIUS);
                this.ele.style.fontSize = 15 * scale + "px";
                this.ele.style.opacity = alpha+0.5;
                this.ele.style.filter = "alpha(opacity = "+(alpha+0.5)*100+")";
                this.ele.style.zIndex = parseInt(scale*100);
                this.ele.style.left = this.x + CX - this.ele.offsetWidth/2 +"px";
                this.ele.style.top = this.y + CY - this.ele.offsetHeight/2 +"px";
            }
        }
        innit();
        animate();
    </script>
</body>
</html>
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原文地址：https://www.cnblogs.com/li-sir/p/7494834.html