移动端利用H5实现压缩图片上传功能

filechooser.onchange = function () {
   if (!this.files.length) return;
 
   var files = Array.prototype.slice.call(this.files);
 
   if (files.length > 9) {
    alert("最多同时只可上传9张图片");
    return;
   }
 
   files.forEach(function (file, i) {
    if (!/\/(?:jpegpnggif)/i.test(file.type)) return;
 
    var reader = new FileReader();
 
    var li = document.createElement("li");
    li.innerHTML = "<div class="progress"><span></span></div>";
    $(".img-list").append($(li));
 
    reader.onload = function () {
     var result = this.result;
     var img = new Image();
     img.src = result;
 
     //如果图片大小小于200kb，则直接上传
     if (result.length <= maxsize) {
      $(li).css("background-image", "url(" + result + ")");
      img = null;
      upload(result, file.type, $(li));
 
      return;
     }
 
 //    图片加载完毕之后进行压缩，然后上传
     if (img.complete) {
      callback();
     } else {
      img.onload = callback;
     }
 
     function callback() {
      var data = compress(img);
 
      $(li).css("background-image", "url(" + data + ")");
 
      upload(data, file.type, $(li));
 
      img = null;
     }
 
    };
 
    reader.readAsDataURL(file);
   })
  };

function compress(img) {
  var initSize = img.src.length;
  var width = img.width;
  var height = img.height;

  //如果图片大于四百万像素，计算压缩比并将大小压至400万以下
  var ratio;
  if ((ratio = width * height / 4000000)>1) {
   ratio = Math.sqrt(ratio);
   width /= ratio;
   height /= ratio;
  }else {
   ratio = 1;
  }

  canvas.width = width;
  canvas.height = height;

//  铺底色
  ctx.fillStyle = "#fff";
  ctx.fillRect(0, 0, canvas.width, canvas.height);

  //如果图片像素大于100万则使用瓦片绘制
  var count;
  if ((count = width * height / 1000000) > 1) {
   count = ~~(Math.sqrt(count)+1); //计算要分成多少块瓦片

//   计算每块瓦片的宽和高
   var nw = ~~(width / count);
   var nh = ~~(height / count);

   tCanvas.width = nw;
   tCanvas.height = nh;

   for (var i = 0; i < count; i++) {
    for (var j = 0; j < count; j++) {
     tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);

     ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
    }
   }
  } else {
   ctx.drawImage(img, 0, 0, width, height);
  }

  //进行最小压缩
  var ndata = canvas.toDataURL("image/jpeg", 0.1);

  console.log("压缩前：" + initSize);
  console.log("压缩后：" + ndata.length);
  console.log("压缩率：" + ~~(100 * (initSize - ndata.length) / initSize) + "%");

  tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;

  return ndata;
 }

// 图片上传，将base64的图片转成二进制对象，塞进formdata上传
 function upload(basestr, type, $li) {
  var text = window.atob(basestr.split(",")[1]);
  var buffer = new ArrayBuffer(text.length);
  var ubuffer = new Uint8Array(buffer);
  var pecent = 0 , loop = null;

  for (var i = 0; i < text.length; i++) {
   ubuffer[i] = text.charCodeAt(i);
  }

  var Builder = window.WebKitBlobBuilder window.MozBlobBuilder;
  var blob;

  if (Builder) {
   var builder = new Builder();
   builder.append(buffer);
   blob = builder.getBlob(type);
  } else {
   blob = new window.Blob([buffer], {type: type});
  }

  var xhr = new XMLHttpRequest();
  var formdata = new FormData();
  formdata.append("imagefile", blob);

  xhr.open("post", "/cupload");

  xhr.onreadystatechange = function () {
   if (xhr.readyState == 4 && xhr.status == 200) {
    console.log("上传成功：" + xhr.responseText);

    clearInterval(loop);

    //当收到该消息时上传完毕
    $li.find(".progress span").animate({"width": "100%"}, pecent < 95 ? 200 : 0, function () {
     $(this).html("上传成功");
    });

    $(".pic-list").append("<a href="" + xhr.responseText + " rel="external nofollow" ">" + xhr.responseText + "<img src="" + xhr.responseText + "" /></a>")
   }
  };

  //数据发送进度，前50%展示该进度
  xhr.upload.addEventListener("progress", function (e) {
   if (loop) return;

   pecent = ~~(100 * e.loaded / e.total) / 2;
   $li.find(".progress span").css("width", pecent + "%");

   if (pecent == 50) {
    mockProgress();
   }
  }, false);

  //数据后50%用模拟进度
  function mockProgress() {
   if (loop) return;

   loop = setInterval(function () {
    pecent++;
    $li.find(".progress span").css("width", pecent + "%");

    if (pecent == 99) {
     clearInterval(loop);
    }
   }, 100)
  }

  xhr.send(formdata);
 }