有时候，我们需要显示一个许多用户组合的一个头像，像扣扣的讨论组头像，微信的群头像，下面是一个简单的实现方法：

首先，获取你需要的头像图片地址，保存在一个对象里面，例如：

var data = []; 然后可以限定组合图片的最大个数，比如限定四个，那么久判断数据库里的图片个数是否大于4，如果大于4，那么就取前四个，如果不大于4，那么就取完。

随后，看注释：

var base64 = []; //用来装合成的图片var c = document_createElement_x_x('canvas'); //创建一个canvasvar ctx = c.getContext('2d');//返回一个用于在画布上绘图的2维环境var len = data.length; //获取需要组合的头像图片的张数var a = 0; //初始化需要组合头像的长度var b = 0; //初始化需要组合头像的宽度c.width = 290; //定义canvas画布的宽度c.height = 290; //定义canvas画布的高度ctx.rect(0, 0, c.width, c.height); //画矩形ctx.fillStyle = '#fff'; //设置矩形颜色ctx.fill(); //关闭并填充该路径

接下来就需要写一个function开始画：

​functiondrawing(n){//参数n是传入的是数字，0表示画第一张图片，1表示第二张。在这里先根据不同的需求设置a,b的大小​，我在这里是4张图是极限，设置的是，n=0时a=b=40;n=1时a=150,b=40,n=2时a=40,b=150,n=3时a=b=150​       if(n < len){//当n<需要组合头像图片个数时就不再重复这个函数var img = new Image();​ //创建一个image对象img.src = data[n];//将图片地址赋值给image对象的srcimg.onload = function(){//图片预加载ctx.drawImage(img, a, b, 100, 100); //在画布上绘制image对象的图片drawing(n+ 1); //再执行此函数}​}else{ //如果执行完了，也就是都画完了，就要显示画好的图像base64.push(c.toDataURL("image/jpg")); //将画好的图像放入base64对象//这里可以写一个返回这个对象，也可以把base64赋值给一个全局变量}}​​

最后，执行这个function:

drawing(0);​

完成操作，在html页面中的img的src里面引用base64的值，就可以显示出来了，但是要注意，这段js要在html页面执行之前执行，不然显示不出来的哦

这是效果：

在这里封装好了一个js：

function groupPic(Images, imgId)
{//Images是图片地址数组，imgId是html页面的img标签的id属性值var base64 = [];var canvas = document.createElement('canvas');var context = canvas.getContext('2d');var len = Images.length;if (len > 9) {len = 9;}//len=8;var a = 0;var b = 0;var k = 80;var l = 80;if (len > 4) {k = 60;l = 60;}canvas.width = 290;canvas.height = 290;context.rect(0, 0, canvas.width, canvas.height);context.fillStyle = '#fff';context.fill();function drawing(n) {if (n < len) {if (len <= 4) {if (len != 3) {if (n == 0) {a = b = 40;} else if (n == 1) {a = 130;b = 40;} else if (n == 2) {a = 40;b = 130;} else if (n == 3) {a = b = 130;}} else {if (n == 0) {a = 75;b = 40;} else if (n == 1) {a = 40;b = 130;} else if (n == 2) {a = 130;b = 130;}}}if (len == 5) {if (n == 0) {a = 70;b = 40;} else if (n == 1) {a = 140;b = 40;} else if (n == 2) {a = 40;b = 110;} else if (n == 3) {a = b = 110;} else {a = 180;b = 110;}}if (len == 6) {if (n == 0) {a = 40;b = 40;} else if (n == 1) {a = 110;b = 40;} else if (n == 2) {a = 180;b = 40;} else if (n == 3) {a = 40;b = 110;} else if (n == 4) {a = b = 110} else {a = 180;b = 110;}}if (len == 7) {if (n == 0) {a = 110;b = 40;} else if (n == 1) {a = 40;b = 110;} else if (n == 2) {a = 110;b = 110;} else if (n == 3) {a = 180;b = 110;} else if (n == 4) {a = 40;b = 180;} else if (n == 5) {a = 110;b = 180;} else {a = b = 180;}}if (len == 8) {if (n == 0) {a = 70;b = 40;} else if (n == 1) {a = 140;b = 40;} else if (n == 2) {a = 40;b = 110;} else if (n == 3) {a = 110;b = 110;} else if (n == 4) {a = 180;b = 110;} else if (n == 5) {a = 40;b = 180;} else if (n == 6) {a = 110;b = 180;} else {a = b = 180;}}if (len == 9) {if (n == 0) {a = 40;b = 40;} else if (n == 1) {a = 110;b = 40;} else if (n == 2) {a = 180;b = 40;} else if (n == 3) {a = 40;b = 110;} else if (n == 4) {a = 110;b = 110;} else if (n == 5) {a = 180;b = 110;} else if (n == 6) {a = 40;b = 180;} else if (n == 7) {a = 110;b = 180;} else {a = b = 180;}}var img = new Image();img.src = Images[n];img.onload = function(){context.drawImage(img, a, b, k, l);drawing(n + 1);}} else {base64.push(canvas.toDataURL("image/jpg"));document.getElementById(imgId).src = base64[0];}}drawing(0);
}

使用方法：在html页面中添加下面的js:

window.onload = function(){var Images = ["1.jpg","2.jpg","3.jpg","4.jpg"];var fun = groupPic;fun(Images, "imageId");
}