在最近一个项目里，要求在上传图片的时候需要要求显示图片缩略图、上传图片数量限制、图片超过一定尺寸、一定的大小就自动进行压缩，最后要求同一个页面上传的文件必须拥有统一的GUID，以此来识别是同一个产品的所有图片。
MVC在上传图片这方面上做得非常的现代，可以通过用极简单的代码进行上传图片。图片压缩我是参考了网上的例程。该代码的原理是将大图片显示在canvas里面，再采用canvas.toDataURL的方法得到base64字符串来实现压缩。
弄清了原理以后，就可以进行js代码进行采样。这里我是参考了这篇博客，但我在实际使用中发现了一个BUG，导致上传时显示“参数无效”。而且由于控制器那里使用了try导致我一时半会不知错误是在那里，延误了开发进程，后来我根据我的需求重新写了这个js。
; (function () {
function detectSubsampling(img) {
var iw = img.naturalWidth, ih = img.naturalHeight;
if (iw * ih > 1024 * 1024) { //大于百万像素的就会进行抽样
var canvas = document.createElement('canvas');
canvas.width = canvas.height = 1;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, -iw + 1, 0);
// subsampled image becomes half smaller in rendering size.
// check alpha channel value to confirm image is covering edge pixel or not.
// if alpha value is 0 image is not covering, hence subsampled.
return ctx.getImageData(0, 0, 1, 1).data[3] === 0;
} else {
return false;
}
}
/**
* Detecting vertical squash in loaded image.
* Fixes a bug which squash image vertically while drawing into canvas for some images.
*/
function detectVerticalSquash(img, iw, ih) {
var canvas = document.createElement('canvas');
canvas.width = 1;
canvas.height = ih;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0);
var data = ctx.getImageData(0, 0, 1, ih).data;
// search image edge pixel position in case it is squashed vertically.
var sy = 0;
var ey = ih;
var py = ih;
while (py > sy) {
var alpha = data[(py - 1) * 4 + 3];
if (alpha === 0) {
ey = py;
} else {
sy = py;
}
py = (ey + sy) >> 1;
}
var ratio = (py / ih);
return (ratio === 0) ? 1 : ratio;
}
/**
* Rendering image element (with resizing) and get its data URL
*/
function renderImageToDataURL(img, options, doSquash) {
var canvas = document.createElement('canvas');
renderImageToCanvas(img, canvas, options, doSquash);
return canvas.toDataURL("image/jpeg", options.quality || 0.8);
}
/**
* Rendering image element (with resizing) into the canvas element
*/
function renderImageToCanvas(img, canvas, options, doSquash) {
var iw = img.naturalWidth, ih = img.naturalHeight;
if (!(iw + ih)) return;
var width = options.width, height = options.height;
var ctx = canvas.getContext('2d');
ctx.save();
transformCoordinate(canvas, ctx, width, height, options.orientation);
var subsampled = detectSubsampling(img);
if (subsampled) {
iw /= 2;
ih /= 2;
}
var d = 1024; // size of tiling canvas
var tmpCanvas = document.createElement('canvas');
tmpCanvas.width = tmpCanvas.height = d;
var tmpCtx = tmpCanvas.getContext('2d');
var vertSquashRatio = doSquash ? detectVerticalSquash(img, iw, ih) : 1;
var dw = Math.ceil(d * width / iw);
var dh = Math.ceil(d * height / ih / vertSquashRatio);
var sy = 0;
var dy = 0;
while (sy < ih) {
var sx = 0;
var dx = 0;
while (sx < iw) {
tmpCtx.clearRect(0, 0, d, d);
tmpCtx.drawImage(img, -sx, -sy);
ctx.drawImage(tmpCanvas, 0, 0, d, d, dx, dy, dw, dh);
sx += d;
dx += dw;
}
sy += d;
dy += dh;
}
ctx.restore();
tmpCanvas = tmpCtx = null;
}
/**
* Transform canvas coordination according to specified frame size and orientation
* 根据帧的大小和方向调整canvas
* 方向值是来自EXIF标签
*/
function transformCoordinate(canvas, ctx, width, height, orientation) {
switch (orientation) {
case 5:
case 6:
case 7:
case 8:
canvas.width = height;
canvas.height = width;
break;
default:
canvas.width = width;
canvas.height = height;
}
switch (orientation) {
case 2:
// horizontal flip
ctx.translate(width, 0);
ctx.scale(-1, 1);
break;
case 3:
// 180 rotate left
ctx.translate(width, height);
ctx.rotate(Math.PI);
break;
case 4:
// vertical flip
ctx.translate(0, height);
ctx.scale(1, -1);
break;
case 5:
// vertical flip + 90 rotate right
ctx.rotate(0.5 * Math.PI);
ctx.scale(1, -1);
break;
case 6:
// 90 rotate right
ctx.rotate(0.5 * Math.PI);
ctx.translate(0, -height);
break;
case 7:
// horizontal flip + 90 rotate right
ctx.rotate(0.5 * Math.PI);
ctx.translate(width, -height);
ctx.scale(-1, 1);
break;
case 8:
// 90 rotate left
ctx.rotate(-0.5 * Math.PI);
ctx.translate(-width, 0);
break;
default:
break;
}
}
var URL = window.URL && window.URL.createObjectURL ? window.URL :
window.webkitURL && window.webkitURL.createObjectURL ? window.webkitURL :
null;
/**
* MegaPixImage class
*/
function MegaPixImage(srcImage) {
if (window.Blob && srcImage instanceof Blob) {
if (!URL) { throw Error("No createObjectURL function found to create blob url"); }
var img = new Image();
img.src = URL.createObjectURL(srcImage);
this.blob = srcImage;
srcImage = img;
}
if (!srcImage.naturalWidth && !srcImage.naturalHeight) {
var _this = this;
srcImage.onload = srcImage.onerror = function () {
var listeners = _this.imageLoadListeners;
if (listeners) {
_this.imageLoadListeners = null;
for (var i = 0, len = listeners.length; i < len; i++) {
listeners[i]();
}
}
};
this.imageLoadListeners = [];
}
this.srcImage = srcImage;
}
/**
* Rendering megapix image into specified target element
*/
MegaPixImage.prototype.render = function (target, options, callback) {
if (this.imageLoadListeners) {
var _this = this;
this.imageLoadListeners.push(function () { _this.render(target, options, callback); });
return;
}
options = options || {};
var imgWidth = this.srcImage.naturalWidth, imgHeight = this.srcImage.naturalHeight,
width = options.width, height = options.height,
maxWidth = options.maxWidth, maxHeight = options.maxHeight,
doSquash = !this.blob || this.blob.type === 'image/jpeg';
if (width && !height) {
height = (imgHeight * width / imgWidth) << 0;
} else if (height && !width) {
width = (imgWidth * height / imgHeight) << 0;
} else {
width = imgWidth;
height = imgHeight;
}
if (maxWidth && width > maxWidth) {
width = maxWidth;
height = (imgHeight * width / imgWidth) << 0;
}
if (maxHeight && height > maxHeight) {
height = maxHeight;
width = (imgWidth * height / imgHeight) << 0;
}
var opt = { width: width, height: height };
for (var k in options) opt[k] = options[k];
target.tagName = target.tagName || "IMG";
var tagName = target.tagName.toLowerCase();
if (tagName === 'img') {
target.src = renderImageToDataURL(this.srcImage, opt, doSquash);
} else if (tagName === 'canvas') {
renderImageToCanvas(this.srcImage, target, opt, doSquash);
}
if (typeof this.onrender === 'function') {
this.onrender(target);
}
if (callback) {
callback();
}
if (this.blob) {
this.blob = null;
URL.revokeObjectURL(this.srcImage.src);
}
};
/**
* Export class to global
*/
if (typeof define === 'function' && define.amd) {
define([], function () { return MegaPixImage; }); // for AMD loader
} else if (typeof exports === 'object') {
module.exports = MegaPixImage; // for CommonJS
} else {
this.MegaPixImage = MegaPixImage;
}
})();
; (function ($) {
$.extend($, {
fileUpload: function (options) {
var para = {
multiple: true,
filebutton: ".filePicker",
uploadButton: null,
url: "/me/MUploadImg",
base64strUrl: "/me/MUploadImgBase64Str",
filebase: "mfile",//mvc后台需要对应的名称
auto: true,
previewZoom: null,
uploadComplete: function (res) {
console.log("uploadComplete", res);
uploadCount++;
core.checkComplete();
},
uploadError: function (err) {
console.log("uploadError", err);
},
onProgress: function (percent) { // 提供给外部获取单个文件的上传进度，供外部实现上传进度效果
console.log(percent);
},
};
para = $.extend(para, options);
var $self = $(para.filebutton);
//先加入一个file元素
var multiple = ""; // 设置多选的参数
para.multiple ? multiple = "multiple" : multiple = "";
$self.css('position', 'relative');
$self.append('');
var doms = {
"fileToUpload": $self.find("#fileImage"),
// "thumb": $self.find(".thumb"),
// "progress": $self.find(".upload-progress")
};
function getBase64Image(img) {
var canvas = document.createElement("canvas");
canvas.width = img.width;
canvas.height = img.height;
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0, img.width, img.height);
var dataURL = canvas.toDataURL("image/jpeg");
return dataURL;
// return dataURL.replace("data:image/png;base64,", "");
}
function simpleSize(size) {
if (!size) return "0";
if (size < 1024) {
return size;
}
var kb = size / 1024;
if (kb < 1024) {
return kb.toFixed(2) + "K";
}
var mb = kb / 1024;
if (mb < 1024) {
return mb.toFixed(2) + "M";
}
var gb = mb / 1024;
return gb.toFixed(2) + "G";
};
//Convert DataURL to Blob to send over Ajax
function dataURItoBlob(dataUrl) {
// convert base64 to raw binary data held in a string
// doesn't handle URLEncoded DataURIs - see SO answer #6850276 for code that does this
var byteString = atob(dataUrl.split(',')[1]);
// separate out the mime component
var mimeString = dataUrl.split(',')[0].split(':')[1].split(';')[0];
// write the bytes of the string to an ArrayBuffer
var ab = new ArrayBuffer(byteString.length);
var ia = new Uint8Array(ab);
for (var i = 0; i < byteString.length; i++) {
ia[i] = byteString.charCodeAt(i);
}
return new Blob([ab], { type: 'image/jpeg' });
}
var uploadCount = 0;
var core = {
fileSelected: function () {
var files = $("#fileImage")[0].files;
var count = files.length;
console.log("共有" + count + "个文件");
for (var i = 0; i < count; i++) {
if (i >= para.limitCount) {
imClient.customerSay("最多只能选择"+para.limitCount+"张图片!");
break;
}
var item = files[i];
console.log("原图片大小", item.size);
if (item.size > 1024 * 1024 * 1) {
console.log("图片大于1M，开始进行压缩...");
(function(img) {
var mpImg = new MegaPixImage(img);
var resImg = document.getElementById("resultImage");
resImg.file = img;
mpImg.render(resImg, { maxWidth: 500, maxHeight: 500, quality: 1 }, function() {
var base64 = getBase64Image(resImg);
var base641 = resImg.src;
console.log("base641", base64.length, simpleSize(base64.length), base641.length, simpleSize(base641.length));
if (para.auto) core.uploadBase64str(base641);
});
})(item);
} else {
if (para.auto) core.uploadFile(item);
}
core.previewImage(item);
}
},
uploadBase64str: function (base64Str) {
var guid = $("#guid0").val();
//var blob = dataURItoBlob(base64Str);
//console.log("压缩后的文件大小", blob.size);
//core.uploadFile(blob);
var formdata = new FormData();
formdata.append("base64str", base64Str);
formdata.append("guid", guid);
var xhr = new XMLHttpRequest();
xhr.upload.addEventListener("progress", function (e) {
var percentComplete = Math.round(e.loaded * 100 / e.total);
para.onProgress(percentComplete.toString() + '%');
});
xhr.addEventListener("load", function (e) {
para.uploadComplete(xhr.responseText);
});
xhr.addEventListener("error", function (e) {
para.uploadError(e);
});
xhr.open("post", para.base64strUrl, true);
xhr.send(formdata);
},
uploadFile: function (file) {
console.log("开始上传");
var guid = $("#guid0").val();
var formdata = new FormData();
formdata.append(para.filebase, file);//这个名字要和mvc后台配合
formdata.append("guid", guid);
var xhr = new XMLHttpRequest();
xhr.upload.addEventListener("progress", function (e) {
var percentComplete = Math.round(e.loaded * 100 / e.total);
para.onProgress(percentComplete.toString() + '%');
});
xhr.addEventListener("load", function (e) {
para.uploadComplete(xhr.responseText);
});
xhr.addEventListener("error", function (e) {
para.uploadError(e);
});
xhr.open("post", para.url, true);
xhr.send(formdata);
},
checkComplete:function() {
var all = (doms.fileToUpload)[0].files.length;
if (all == uploadCount) {
console.log(all + "个文件上传完毕");
doms.fileToUpload.remove();
//input有一个问题就是选择重复的文件不会触发change事件，所以做了一个处理，再每次上传完之后删掉这个元素再新增一个input。
$self.append('');
}
},
uploadFiles: function () {
var files = (doms.fileToUpload)[0].files;
for (var i = 0; i < files.length; i++) {
core.uploadFile(files[i]);
}
},
previewImage: function (file) {
if (!para.previewZoom) return;
var img = document.createElement("img");
img.file = file;
$(para.previewZoom).append(img);
// 使用FileReader方法显示图片内容
var reader = new FileReader();
reader.onload = (function (aImg) {
return function (e) {
aImg.src = e.target.result;
};
})(img);
reader.readAsDataURL(file);
}
}
$(document).on("change", "#fileImage", function () {
core.fileSelected();
});
$(document).on("click", para.filebutton, function () {
console.log("clicked");
});
if (para.uploadButton) {
$(document).on("click", para.uploadButton, function () {
core.uploadFiles();
});
}
}
});
})(jQuery);
在视图中，我用了最简单的页面进行调试：
@{
Layout = null;
}
h5图片压缩与上传
UploadImg
点击选择文件
![]()
ViewBag.uid是在控制器里面直接生成的，这里我为了调试方便，直接采用type="text" 进行赋值，在实际应用可以采用hidden。
下面是控制器的内容：
public ActionResult Uptest()
{
ViewBag.uid = Guid.NewGuid();
return View();
}
[HttpPost]
public ActionResult MUploadImg(HttpPostedFileBase mfile,string guid)
{
return UploadImg(mfile,guid);
}
[HttpPost]
public ActionResult UploadImg(HttpPostedFileBase file,string guid)
{
if (file != null)
{
var path = "~/uploads/";
var uploadpath = Server.MapPath(path);
if (!Directory.Exists(uploadpath))
{
Directory.CreateDirectory(uploadpath);
}
string fileName = Path.GetFileName(file.FileName);// 原始文件名称
string fileExtension = Path.GetExtension(fileName); // 文件扩展名
string saveName = Guid.NewGuid() + fileExtension; // 保存文件名称 这是个好方法。
//string saveName = Encrypt.GenerateOrderNumber() + fileExtension; // 保存文件名称 这是个好方法。
file.SaveAs(uploadpath + saveName);
return Json(new { Success = true, SaveName = path + saveName+' '+guid });
}
return Json(new { Success = false, Message = "请选择要上传的文件！" }, JsonRequestBehavior.AllowGet);
}
[HttpPost]
public ActionResult MUploadImgBase64Str(string base64str, string guid)
{
var imgData = base64str.Split(',')[1];
//过滤特殊字符即可
string dummyData = imgData.Trim().Replace("%", "").Replace(",", "").Replace(" ", "+");
if (dummyData.Length % 4 > 0)
{
dummyData = dummyData.PadRight(dummyData.Length + 4 - dummyData.Length % 4, '=');
}
byte[] byteArray = Convert.FromBase64String(dummyData);
using (System.IO.MemoryStream ms = new System.IO.MemoryStream(byteArray))
{
Image img = Image.FromStream(ms);
var path = "~/uploads/";
var uploadpath = Server.MapPath(path);
var saveName = uploadpath + "stoneniqiu" + ".jpg";
img.Save(saveName);
return Json(new { Success = true, SaveName = saveName+' '+guid });
}
}
在控制器中，我首先传递一个Guid 到视图，然后用AJAX提交，又回到控制器获取，这是为了生成一个唯一而又统一的Guid 。在真实应用中，这里是上传文件成功之后做一个写入数据库的动作，这里是为了测试，我仅仅让它在成功处输出，再到js用console.log 输出在浏览器中显示。
js文件的思路非常不错，提交文件以后，通过判断图像的大小进行处理，文件大于某个字节以后就采样在canvas里面显示，再通过canvas.toDataURL的方法得到base64字符串来实现压缩。前端压缩的好处是速度快。