这个功能可以快速地将已写好的html页面生成为canvas，可用于展示或者通过js保存为图片
使用流程：首先，使用html2canvas将已画好的html页面转为canvas，然后，通过使用Canvas2Image 保存为图片
引用：
html2canvas官网：http://html2canvas.hertzen.com/
html2canvas github:https://github.com/niklasvh/html2canvas
Canvas2Image github:https://github.com/hongru/canvas2image(文末有Canvas2Image.js文件可直接下载)
使用：npm install --save html2canvas 或者直接在官网下载js文件，然后在页面引用
#html
保存为图片
#js
//引用
import Canvas2Image from '@/utils/canvas2Image.js'
import html2canvas from 'html2canvas'
//具体代码
savePoster(){
let that = this
//打开loading
that.savePosterLoading = true
//生成图片之前，需先将整体的滚动条隐藏掉，否则生成出来的照片会偏移
document.getElementById('app').style.overflowY = 'hidden'
//两个参数：所需要截图的元素id，截图后要执行的函数， canvas为截图后返回的最后一个canvas
var shareContent = document.getElementById('screenViewBox');
var width = shareContent.offsetWidth;
var height = shareContent.offsetHeight;
var canvas = document.createElement("canvas");
var scale = 5; //这里为了下载出更清晰的图片，值越大越清晰
canvas.width = width * scale;
canvas.height = height * scale;
canvas.getContext("2d").scale(scale, scale);
var opts = {
scale: 1,//不管上面的scale是多少倍，这里只能取1，否则会显示不完全
canvas: canvas,
logging: true,
width: width,
height: height
};
let downloadName = '下载的图片名称'
html2canvas(shareContent,opts).then(
function(canvas) {
//这个方式是直接将canvas保存为图片的，具体参数可自行查看源码
var img = Canvas2Image.saveAsImage(canvas, canvas.width, canvas.height,'PNG',downloadName);
//这个方式只是提供展示图片的功能，暂时没有用到
// var img = Canvas2Image.convertToPNG(canvas, canvas.width, canvas.height,'PNG');
// document.body.appendChild(img);
//生成图片之前，需先将整体的滚动恢复为之前的状态
document.getElementById('app').style.overflowY = 'scroll'
//关闭loading
that.savePosterLoading = false
},
);
},
canvas2Image.js文件
/**
* covert canvas to image
* and save the image file
*/
const Canvas2Image = (function () {
// check if support sth.
const $support = (function () {
const canvas = document.createElement("canvas"),
ctx = canvas.getContext("2d");
return {
canvas: !!ctx,
imageData: !!ctx.getImageData,
dataURL: !!canvas.toDataURL,
btoa: !!window.btoa,
};
})();
const downloadMime = "image/octet-stream";
function scaleCanvas(canvas, width, height) {
const w = canvas.width,
h = canvas.height;
if (width === undefined) {
width = w;
}
if (height === undefined) {
height = h;
}
let retCanvas = document.createElement("canvas");
let retCtx = retCanvas.getContext("2d");
retCanvas.width = width;
retCanvas.height = height;
retCtx.drawImage(canvas, 0, 0, w, h, 0, 0, width, height);
// retCtx.drawImage(canvas, 0,0, w, h, 10, 10, width, height);
return retCanvas;
}
function getDataURL(canvas, type, width, height) {
canvas = scaleCanvas(canvas, width, height);
return canvas.toDataURL(type);
}
// save file to local with file name and file type
function saveFile(strData, fileType, fileName = "name") {
// document.location.href = strData;
let saveLink = document.createElement("a");
// download file name
saveLink.download = fileName + "." + fileType;
// download file data
saveLink.href = strData;
// start download
saveLink.click();
}
function genImage(strData) {
let img = document.createElement("img");
img.src = strData;
return img;
}
function fixType(type) {
type = type.toLowerCase().replace(/jpg/i, "jpeg");
const r = type.match(/png|jpeg|bmp|gif/)[0];
return "image/" + r;
}
function encodeData(data) {
if (!window.btoa) {
// eslint-disable-next-line no-throw-literal
throw "btoa undefined";
}
let str = "";
if (typeof data == "string") {
str = data;
} else {
for (let i = 0; i < data.length; i++) {
str += String.fromCharCode(data[i]);
}
}
return btoa(str);
}
// function getImageData(canvas) {
// const w = canvas.width,
// h = canvas.height;
// return canvas.getContext("2d").getImageData(0, 0, w, h);
// }
function getImageData(canvas) {
const w = canvas.width,
h = canvas.height;
return canvas.getContext("2d").getImageData(50, 30, w, h);
}
function makeURI(strData, type) {
return "data:" + type + ";base64," + strData;
}
/**
* create bitmap image
* 按照规则生成图片响应头和响应体
*/
const genBitmapImage = function (oData) {
//
// BITMAPFILEHEADER: http://msdn.microsoft.com/en-us/library/windows/desktop/dd183374(v=vs.85).aspx
// BITMAPINFOHEADER: http://msdn.microsoft.com/en-us/library/dd183376.aspx
//
const biWidth = oData.width;
const biHeight = oData.height;
const biSizeImage = biWidth * biHeight * 3;
const bfSize = biSizeImage + 54; // total header size = 54 bytes
//
// typedef struct tagBITMAPFILEHEADER {
// WORD bfType;
// DWORD bfSize;
// WORD bfReserved1;
// WORD bfReserved2;
// DWORD bfOffBits;
// } BITMAPFILEHEADER;
//
const BITMAPFILEHEADER = [
// WORD bfType -- The file type signature; must be "BM"
0x42,
0x4d,
// DWORD bfSize -- The size, in bytes, of the bitmap file
bfSize & 0xff,
(bfSize >> 8) & 0xff,
(bfSize >> 16) & 0xff,
(bfSize >> 24) & 0xff,
// WORD bfReserved1 -- Reserved; must be zero
0,
0,
// WORD bfReserved2 -- Reserved; must be zero
0,
0,
// DWORD bfOffBits -- The offset, in bytes, from the beginning of the BITMAPFILEHEADER structure to the bitmap bits.
54,
0,
0,
0,
];
//
// typedef struct tagBITMAPINFOHEADER {
// DWORD biSize;
// LONG biWidth;
// LONG biHeight;
// WORD biPlanes;
// WORD biBitCount;
// DWORD biCompression;
// DWORD biSizeImage;
// LONG biXPelsPerMeter;
// LONG biYPelsPerMeter;
// DWORD biClrUsed;
// DWORD biClrImportant;
// } BITMAPINFOHEADER, *PBITMAPINFOHEADER;
//
const BITMAPINFOHEADER = [
// DWORD biSize -- The number of bytes required by the structure
40,
0,
0,
0,
// LONG biWidth -- The width of the bitmap, in pixels
biWidth & 0xff,
(biWidth >> 8) & 0xff,
(biWidth >> 16) & 0xff,
(biWidth >> 24) & 0xff,
// LONG biHeight -- The height of the bitmap, in pixels
biHeight & 0xff,
(biHeight >> 8) & 0xff,
(biHeight >> 16) & 0xff,
(biHeight >> 24) & 0xff,
// WORD biPlanes -- The number of planes for the target device. This value must be set to 1
1,
0,
// WORD biBitCount -- The number of bits-per-pixel, 24 bits-per-pixel -- the bitmap
// has a maximum of 2^24 colors (16777216, Truecolor)
24,
0,
// DWORD biCompression -- The type of compression, BI_RGB (code 0) -- uncompressed
0,
0,
0,
0,
// DWORD biSizeImage -- The size, in bytes, of the image. This may be set to zero for BI_RGB bitmaps
biSizeImage & 0xff,
(biSizeImage >> 8) & 0xff,
(biSizeImage >> 16) & 0xff,
(biSizeImage >> 24) & 0xff,
// LONG biXPelsPerMeter, unused
0,
0,
0,
0,
// LONG biYPelsPerMeter, unused
0,
0,
0,
0,
// DWORD biClrUsed, the number of color indexes of palette, unused
0,
0,
0,
0,
// DWORD biClrImportant, unused
0,
0,
0,
0,
];
const iPadding = (4 - ((biWidth * 3) % 4)) % 4;
const aImgData = oData.data;
let strPixelData = "";
const biWidth4 = biWidth << 2;
let y = biHeight;
const fromCharCode = String.fromCharCode;
do {
const iOffsetY = biWidth4 * (y - 1);
let strPixelRow = "";
for (let x = 0; x < biWidth; x++) {
const iOffsetX = x << 2;
strPixelRow +=
fromCharCode(aImgData[iOffsetY + iOffsetX + 2]) +
fromCharCode(aImgData[iOffsetY + iOffsetX + 1]) +
fromCharCode(aImgData[iOffsetY + iOffsetX]);
}
for (let c = 0; c < iPadding; c++) {
strPixelRow += String.fromCharCode(0);
}
strPixelData += strPixelRow;
} while (--y);
return (
encodeData(BITMAPFILEHEADER.concat(BITMAPINFOHEADER)) +
encodeData(strPixelData)
);
};
/**
* saveAsImage
* @param canvas canvasElement
* @param width {String} image type
* @param height {Number} [optional] png width
* @param type {string} [optional] png height
* @param fileName {String} image name
*/
const saveAsImage = function (canvas, width, height, type, fileName) {
// save file type
const fileType = type;
if ($support.canvas && $support.dataURL) {
if (typeof canvas == "string") {
canvas = document.getElementById(canvas);
}
if (type === undefined) {
type = "png";
}
type = fixType(type);
if (/bmp/.test(type)) {
const data = getImageData(scaleCanvas(canvas, width, height));
const strData = genBitmapImage(data);
// use new parameter: fileType
saveFile(makeURI(strData, downloadMime), fileType, fileName);
} else {
const strData = getDataURL(canvas, type, width, height);
// use new parameter: fileType
saveFile(strData.replace(type, downloadMime), fileType, fileName);
}
}
};
const convertToImage = function (canvas, width, height, type) {
if ($support.canvas && $support.dataURL) {
if (typeof canvas == "string") {
canvas = document.getElementById(canvas);
}
if (type === undefined) {
type = "png";
}
type = fixType(type);
if (/bmp/.test(type)) {
const data = getImageData(scaleCanvas(canvas, width, height));
const strData = genBitmapImage(data);
return genImage(makeURI(strData, "image/bmp"));
} else {
const strData = getDataURL(canvas, type, width, height);
return genImage(strData);
}
}
};
return {
saveAsImage: saveAsImage,
saveAsPNG: function (canvas, width, height, fileName) {
return saveAsImage(canvas, width, height, "png", fileName);
},
saveAsJPEG: function (canvas, width, height, fileName) {
return saveAsImage(canvas, width, height, "jpeg", fileName);
},
saveAsGIF: function (canvas, width, height, fileName) {
return saveAsImage(canvas, width, height, "gif", fileName);
},
saveAsBMP: function (canvas, width, height, fileName) {
return saveAsImage(canvas, width, height, "bmp", fileName);
},
convertToImage: convertToImage,
convertToPNG: function (canvas, width, height) {
return convertToImage(canvas, width, height, "png");
},
convertToJPEG: function (canvas, width, height) {
return convertToImage(canvas, width, height, "jpeg");
},
convertToGIF: function (canvas, width, height) {
return convertToImage(canvas, width, height, "gif");
},
convertToBMP: function (canvas, width, height) {
return convertToImage(canvas, width, height, "bmp");
},
};
})();
// Export function, used in npm
export default Canvas2Image;