JavaScript Canvas 合成多张图片并实现下载

 <div class="pho-bg">
 <img src="ossweb-img/man-1.png" class="man man-1" id="man-1" alt="">
 <img src="ossweb-img/man-2.png" class="man man-2" id="man-2" alt="">
 <img src="ossweb-img/man-3.png" class="man man-3" id="man-3" alt="">
 <img src="ossweb-img/man-4.png" class="man man-4" id="man-4" alt="">
 <a href="javascript:;" class="btn" title=""></a>
 <img src="ossweb-img/sen.png" class="sen1" id="sen1" alt="">
 <img id="show-pic" alt="">
 </div>
 <div class="photo"></div>
 <canvas id="myCanvas" width="750" height="1180"></canvas>
 <img src="ossweb-img/bg1.jpg" id="bg1" alt="">
 <img src="ossweb-img/btn.png" id="btn1" alt="">

$('.btn').click(function() {
 $('.pho-bg').hide();
 // $('#myCanvas').show();
 var man1 = document.getElementById("man-1"),
 man2 = document.getElementById("man-2"),
 man3 = document.getElementById("man-3"),
 man4 = document.getElementById("man-4"),
 sen1 = document.getElementById("sen1"),
 btn1 = document.getElementById("btn1"),
 canvasBg = document.getElementById("bg1");
 
 
 var canvas = document.getElementById("myCanvas");
 ctx = canvas.getContext("2d");
 canvas.width = 750;
 canvas.height = 1180;
 // 制作背景图
 var patBg = ctx.createPattern(canvasBg, "repeat");
 ctx.rect(0, 0, 750, 1180);
 ctx.fillStyle = patBg;
 ctx.fill();
 // 将man1,man2,man3,man4,sen1,btn加入画布
 ctx.drawImage(man1, 0, 0, 341, 474);
 ctx.drawImage(man2, 410, 0, 341, 474);
 ctx.drawImage(man3, 0, 474, 341, 474);
 ctx.drawImage(man4, 410, 474, 341, 474);
 
 ctx.drawImage(sen1, 40, 950, 669, 109);
 ctx.drawImage(btn1, 150, 350, 449, 288);
 var newImg = new Image();
 newImg.src = canvas.toDataURL("image/png");
 
 $('.photo').append(newImg);
 
 });