解析3D标签云，其实很简单
Posted 一梦_浮生
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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> <a class="tag" target="_blank" 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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">我喜欢你</a> <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> <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">我喜欢你</a> <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" 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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)CSS3三维变形，其实很简单！