技术要点
- FileReader去读取图片
- 使用canvas的API去压缩
- buffer处理后上传
HTML
<input type="file" id="choose" accept="image/*" multiple>
<ul class="img-list"></ul>
<a id="upload">上传图片</a>
<span class="tips">只允许上传jpg、png及gif</span>
<div class="pic-list">
你上传的图片(图片有效期为1分钟)：
</div>
JS(使用jQuery库)
var filechooser = document.getElementById("choose");
// 用于压缩图片的canvas
var canvas = document.createElement("canvas");
var ctx = canvas.getContext('2d');
// 瓦片canvas
var tCanvas = document.createElement("canvas");
var tctx = tCanvas.getContext("2d");
var maxsize = 100 * 1024;//自定义只对超过100kb的图片进行压缩
$("#upload").on("click", function() {
filechooser.click();
})
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 (!/\/(?:jpeg|png|gif)/i.test(file.type)) return;
var reader = new FileReader();
var li = document.createElement("li");
// 获取图片大小
var size = file.size / 1024 > 1024 ? (~~(10 * file.size / 1024 / 1024)) / 10 + "MB" : ~~(file.size / 1024) + "KB";
li.innerHTML = '<div class="progress"><span></span></div><div class="size">' + size + '</div>';
$(".img-list").append($(li));
// 读取图片后触发
reader.onload = function() {
var result = this.result;
var img = new Image();
img.src = result;
$(li).css("background-image", "url(" + result + ")");
//如果图片大小小于100kb，则直接上传
if (result.length <= maxsize) {
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 {
// 浏览器显示原图后触发callback进行压缩上传
img.onload = callback;
}
function callback() {
var data = compress(img);
upload(data, file.type, $(li));
img = null;
}
};
// 去读取选择的文件到内存
reader.readAsDataURL(file);
})
};
// 使用canvas对大图片进行压缩
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) {
// ~~ 的作用类似于Math.floor(),性能会好一点
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;
// 先画一个小的tctx，然后将小的从左到右，从上到下画到大的ctx画布上
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（真正压缩的api）
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) {
// 截取图片base64的数据然后转为二进制数据，atob与btoa是一对api
var text = window.atob(basestr.split(",")[1]);
// Uint8Array: 对象 8 位无符号整数值的类型化数组。内容将初始化为 0
var buffer = new Uint8Array(text.length);
var pecent = 0, loop = null;
for (var i = 0; i < text.length; i++) {
buffer[i] = text.charCodeAt(i);
}
var blob = getBlob([buffer], type);
var xhr = new XMLHttpRequest();
// 新建表单对象
var formdata = getFormData();
formdata.append('file', blob);
formdata.append('desc', 'compress_upload');
formdata.append('tel', 'tel');
xhr.open('post', '/upload_compress');
xhr.onreadystatechange = function() {
if (xhr.readyState == 4 && xhr.status == 200) {
console.log(xhr);
var jsonData = JSON.parse(xhr.responseText);
var imagedata = jsonData[0] || {};
var text = imagedata.path ? '上传成功' : '上传失败';
console.log(text + '：' + imagedata.path);
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(text);
});
if (!imagedata.path) return;
$(".pic-list").append('<a href="' + imagedata.path + '">' + imagedata.name + '（' + imagedata.size + '）</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)
}
// 上传
xhr.send(formdata);
}
/**
* 获取blob对象的兼容性写法
* @param {string} buffer 文件内容
* @param {string} format 文件类别
* @return {Blob} 二进制文件的容器
*/
function getBlob(buffer, format) {
try {
return new Blob(buffer, {type: format});
} catch (e) {
var bb = new (window.BlobBuilder || window.WebKitBlobBuilder || window.MSBlobBuilder);
buffer.forEach(function(buf) {
bb.append(buf);
});
return bb.getBlob(format);
}
}
/**
* 获取formdata
*/
function getFormData() {
// 检测浏览器
var isNeedShim = ~navigator.userAgent.indexOf('Android')
&& ~navigator.vendor.indexOf('Google')
&& !~navigator.userAgent.indexOf('Chrome')
&& navigator.userAgent.match(/AppleWebKit\/(\d+)/).pop() <= 534;
return isNeedShim ? new FormDataShim() : new FormData()
}
/**
* formdata 补丁, 给不支持formdata上传blob的android机打补丁
* @constructor
*/
function FormDataShim() {
console.warn('using formdata shim');
var o = this,
parts = [],
boundary = Array(21).join('-') + (+new Date() * (1e16 * Math.random())).toString(36),
oldSend = XMLHttpRequest.prototype.send;
this.append = function(name, value, filename) {
parts.push('--' + boundary + '\r\nContent-Disposition: form-data; name="' + name + '"');
if (value instanceof Blob) {
parts.push('; filename="' + (filename || 'blob') + '"\r\nContent-Type: ' + value.type + '\r\n\r\n');
parts.push(value);
}
else {
parts.push('\r\n\r\n' + value);
}
parts.push('\r\n');
};
// Override XHR send()
XMLHttpRequest.prototype.send = function(val) {
var fr,
data,
oXHR = this;
if (val === o) {
// Append the final boundary string
parts.push('--' + boundary + '--\r\n');
// Create the blob
data = getBlob(parts);
// Set up and read the blob into an array to be sent
fr = new FileReader();
fr.onload = function() {
oldSend.call(oXHR, fr.result);
};
fr.onerror = function(err) {
throw err;
};
fr.readAsArrayBuffer(data);
// Set the multipart content type and boudary
this.setRequestHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);
XMLHttpRequest.prototype.send = oldSend;
}
else {
oldSend.call(this, val);
}
};
}
done
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