使用html2canvas在前端生成图片并下载
1. 需求
在PC网页端，和手机H5端可实现点击拍照按钮将整个页面保存并下载成图片。（其实跟手机的滚动截屏差不多）
2. 准备工作
只需这两个文件：
- html2canvas.1.0.min.js 下载地址：html2canvas.1.0.min.js
- canvas2image.js 下文 会把该文件内容贴上
3. 实现
1.首先写一个按钮（下面所引用的图片在下问贴出）
<div id="btnSave" onclick="screenshot()" style="display: flex;background-color: #b6b8b6;
position: fixed;right: 5%;bottom: 5%;width: 50px;height: 50px;
cursor: pointer;border-radius: 50%;visibility: visible;box-shadow: 0 2px 2px 0 rgb(0 0 0 / 14%), 0 1px 5px 0 rgb(0 0 0 / 12%), 0 3px 1px -2px rgb(0 0 0 / 20%);">
<img src="../images/camera.png" style="
width: 26px;height: 26px;
max-width: 100%; border-style: none;
position: absolute;top: 50%;left: 50%;margin-top: -13px;margin-left: -13px;
" />
</div>
<div id="images" style="display: none;"></div>
2.编写点击事件
//截图
/*生成canvas图形*/
var btnSave = document.getElementById("btnSave");
// 进行canvas生成
btnSave.onclick = function(){
//debugger;
$('#btnSave').hide();
// $('.scoll_bottom_background').remove();
html2canvas(document.querySelector('.container-fluid'),{useCORS: true}).then(canvas => {
//添加属性
canvas.setAttribute('id','thecanvas');
//读取属性值
var value= canvas.getAttribute('id');
document.getElementById('images').appendChild(canvas);
var oCanvas = document.getElementById("thecanvas");
/*自动保存为png*/
// 获取图片资源
var img_data1 = Canvas2Image.saveAsPNG(oCanvas, true).getAttribute('src');
saveFile(img_data1, 'abc');
});
$('#btnSave').show();
}
// 保存文件函数
var saveFile = function(data, filename){
//var save_link = document.createElementNS('http://www.w3.org/1999/xhtml', 'a');
var save_link = document.createElement('a');
save_link.href = data;
save_link.download = filename;
save_link.style.display = 'none';
var event = document.createEvent('MouseEvents');
event.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
save_link.dispatchEvent(event);
};
注：该方法只适用于 手机端H5和PC浏览器，如果想在app中也适用，需要跟安卓大佬沟通怎么把图下载下来。
4.补充资料
jQuery 自行下载吧
1.canvas2image.js
/*
* Canvas2Image v0.1
* Copyright (c) 2008 Jacob Seidelin, jseidelin@nihilogic.dk
* MIT License [http://www.opensource.org/licenses/mit-license.php]
*/
var Canvas2Image = (function() {
// check if we have canvas support
var bHasCanvas = false;
var oCanvas = document.createElement("canvas");
if (oCanvas.getContext("2d")) {
bHasCanvas = true;
}
// no canvas, bail out.
if (!bHasCanvas) {
return {
saveAsBMP : function(){},
saveAsPNG : function(){},
saveAsJPEG : function(){}
}
}
var bHasImageData = !!(oCanvas.getContext("2d").getImageData);
var bHasDataURL = !!(oCanvas.toDataURL);
var bHasBase64 = !!(window.btoa);
var strDownloadMime = "image/octet-stream";
// ok, we're good
var readCanvasData = function(oCanvas) {
var iWidth = parseInt(oCanvas.width);
var iHeight = parseInt(oCanvas.height);
return oCanvas.getContext("2d").getImageData(0,0,iWidth,iHeight);
}
// base64 encodes either a string or an array of charcodes
var encodeData = function(data) {
var strData = "";
if (typeof data == "string") {
strData = data;
} else {
var aData = data;
for (var i=0;i<aData.length;i++) {
strData += String.fromCharCode(aData[i]);
}
}
return btoa(strData);
}
// creates a base64 encoded string containing BMP data
// takes an imagedata object as argument
var createBMP = function(oData) {
var aHeader = [];
var iWidth = oData.width;
var iHeight = oData.height;
aHeader.push(0x42); // magic 1
aHeader.push(0x4D);
var iFileSize = iWidth*iHeight*3 + 54; // total header size = 54 bytes
aHeader.push(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
aHeader.push(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
aHeader.push(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
aHeader.push(iFileSize % 256);
aHeader.push(0); // reserved
aHeader.push(0);
aHeader.push(0); // reserved
aHeader.push(0);
aHeader.push(54); // dataoffset
aHeader.push(0);
aHeader.push(0);
aHeader.push(0);
var aInfoHeader = [];
aInfoHeader.push(40); // info header size
aInfoHeader.push(0);
aInfoHeader.push(0);
aInfoHeader.push(0);
var iImageWidth = iWidth;
aInfoHeader.push(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
aInfoHeader.push(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
aInfoHeader.push(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
aInfoHeader.push(iImageWidth % 256);
var iImageHeight = iHeight;
aInfoHeader.push(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
aInfoHeader.push(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
aInfoHeader.push(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
aInfoHeader.push(iImageHeight % 256);
aInfoHeader.push(1); // num of planes
aInfoHeader.push(0);
aInfoHeader.push(24); // num of bits per pixel
aInfoHeader.push(0);
aInfoHeader.push(0); // compression = none
aInfoHeader.push(0);
aInfoHeader.push(0);
aInfoHeader.push(0);
var iDataSize = iWidth*iHeight*3;
aInfoHeader.push(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
aInfoHeader.push(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
aInfoHeader.push(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
aInfoHeader.push(iDataSize % 256);
for (var i=0;i<16;i++) {
aInfoHeader.push(0); // these bytes not used
}
var iPadding = (4 - ((iWidth * 3) % 4)) % 4;
var aImgData = oData.data;
var strPixelData = "";
var y = iHeight;
do {
var iOffsetY = iWidth*(y-1)*4;
var strPixelRow = "";
for (var x=0;x<iWidth;x++) {
var iOffsetX = 4*x;
strPixelRow += String.fromCharCode(aImgData[iOffsetY+iOffsetX+2]);
strPixelRow += String.fromCharCode(aImgData[iOffsetY+iOffsetX+1]);
strPixelRow += String.fromCharCode(aImgData[iOffsetY+iOffsetX]);
}
for (var c=0;c<iPadding;c++) {
strPixelRow += String.fromCharCode(0);
}
strPixelData += strPixelRow;
} while (--y);
var strEncoded = encodeData(aHeader.concat(aInfoHeader)) + encodeData(strPixelData);
return strEncoded;
}
// sends the generated file to the client
var saveFile = function(strData) {
document.location.href = strData;
}
var makeDataURI = function(strData, strMime) {
return "data:" + strMime + ";base64," + strData;
}
// generates a <img> object containing the imagedata
var makeImageObject = function(strSource) {
var oImgElement = document.createElement("img");
oImgElement.src = strSource;
return oImgElement;
}
var scaleCanvas = function(oCanvas, iWidth, iHeight) {
if (iWidth && iHeight) {
var oSaveCanvas = document.createElement("canvas");
oSaveCanvas.width = iWidth;
oSaveCanvas.height = iHeight;
oSaveCanvas.style.width = iWidth+"px";
oSaveCanvas.style.height = iHeight+"px";
var oSaveCtx = oSaveCanvas.getContext("2d");
oSaveCtx.drawImage(oCanvas, 0, 0, oCanvas.width, oCanvas.height, 0, 0, iWidth, iHeight);
return oSaveCanvas;
}
return oCanvas;
}
return {
saveAsPNG : function(oCanvas, bReturnImg, iWidth, iHeight) {
if (!bHasDataURL) {
return false;
}
var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight);
var strData = oScaledCanvas.toDataURL("image/png");
if (bReturnImg) {
return makeImageObject(strData);
} else {
saveFile(strData.replace("image/png", strDownloadMime));
}
return true;
},
saveAsJPEG : function(oCanvas, bReturnImg, iWidth, iHeight) {
if (!bHasDataURL) {
return false;
}
var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight);
var strMime = "image/jpeg";
var strData = oScaledCanvas.toDataURL(strMime);
// check if browser actually supports jpeg by looking for the mime type in the data uri.
// if not, return false
if (strData.indexOf(strMime) != 5) {
return false;
}
if (bReturnImg) {
return makeImageObject(strData);
} else {
saveFile(strData.replace(strMime, strDownloadMime));
}
return true;
},
saveAsBMP : function(oCanvas, bReturnImg, iWidth, iHeight) {
if (!(bHasImageData && bHasBase64)) {
return false;
}
var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight);
var oData = readCanvasData(oScaledCanvas);
var strImgData = createBMP(oData);
if (bReturnImg) {
return makeImageObject(makeDataURI(strImgData, "image/bmp"));
} else {
saveFile(makeDataURI(strImgData, strDownloadMime));
}
return true;
}
};
})();
- 图片(透明背景 白色照相机 不知道你们能不能看出来！！！)