html2canvas和canvas2image将dom元素转化成图片
原文链接： https://blog.csdn.net/weixin_39003573/article/details/82467508
1.依赖的文件
html2canvas官网：
http://html2canvas.hertzen.com/?utm_source=caibaojian.com
js地址：http://html2canvas.hertzen.com/dist/html2canvas.jscanvas2image：
/**
* covert canvas to image
* and save the image file
*/
var Canvas2Image = function () {
// check if support sth.
var $support = function () {
var canvas = document.createElement('canvas'),
ctx = canvas.getContext('2d');
return {
canvas: !!ctx,
imageData: !!ctx.getImageData,
dataURL: !!canvas.toDataURL,
btoa: !!window.btoa
};
}();
var downloadMime = 'image/octet-stream';
function scaleCanvas (canvas, width, height) {
var w = canvas.width,
h = canvas.height;
if (width == undefined) {
width = w;
}
if (height == undefined) {
height = h;
}
var retCanvas = document.createElement('canvas');
var retCtx = retCanvas.getContext('2d');
retCanvas.width = width;
retCanvas.height = height;
retCtx.drawImage(canvas, 0, 0, w, h, 0, 0, width, height);
return retCanvas;
}
function getDataURL (canvas, type, width, height) {
canvas = scaleCanvas(canvas, width, height);
return canvas.toDataURL(type);
}
function saveFile (strData) {
document.location.href = strData;
}
function genImage(strData) {
var img = document.createElement('img');
img.src = strData;
return img;
}
function fixType (type) {
type = type.toLowerCase().replace(/jpg/i, 'jpeg');
var r = type.match(/png|jpeg|bmp|gif/)[0];
return 'image/' + r;
}
function encodeData (data) {
if (!window.btoa) { throw 'btoa undefined' }
var str = '';
if (typeof data == 'string') {
str = data;
} else {
for (var i = 0; i < data.length; i ++) {
str += String.fromCharCode(data[i]);
}
}
return btoa(str);
}
function getImageData (canvas) {
var w = canvas.width,
h = canvas.height;
return canvas.getContext('2d').getImageData(0, 0, w, h);
}
function makeURI (strData, type) {
return 'data:' + type + ';base64,' + strData;
}
/**
* create bitmap image
* 鎸夌収瑙勫垯鐢熸垚鍥剧墖鍝嶅簲澶村拰鍝嶅簲浣�
*/
var 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
//
var biWidth = oData.width;
var biHeight = oData.height;
var biSizeImage = biWidth * biHeight * 3;
var bfSize = biSizeImage + 54; // total header size = 54 bytes
//
// typedef struct tagBITMAPFILEHEADER {
// WORD bfType;
// DWORD bfSize;
// WORD bfReserved1;
// WORD bfReserved2;
// DWORD bfOffBits;
// } BITMAPFILEHEADER;
//
var 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;
//
var 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
];
var iPadding = (4 - ((biWidth * 3) % 4)) % 4;
var aImgData = oData.data;
var strPixelData = '';
var biWidth4 = biWidth<<2;
var y = biHeight;
var fromCharCode = String.fromCharCode;
do {
var iOffsetY = biWidth4*(y-1);
var strPixelRow = '';
for (var x = 0; x < biWidth; x++) {
var iOffsetX = x<<2;
strPixelRow += fromCharCode(aImgData[iOffsetY+iOffsetX+2]) +
fromCharCode(aImgData[iOffsetY+iOffsetX+1]) +
fromCharCode(aImgData[iOffsetY+iOffsetX]);
}
for (var c = 0; c < iPadding; c++) {
strPixelRow += String.fromCharCode(0);
}
strPixelData += strPixelRow;
} while (--y);
var strEncoded = encodeData(BITMAPFILEHEADER.concat(BITMAPINFOHEADER)) + encodeData(strPixelData);
return strEncoded;
};
/**
* saveAsImage
* @param canvasElement
* @param {String} image type
* @param {Number} [optional] png width
* @param {Number} [optional] png height
*/
var saveAsImage = function (canvas, width, height, type) {
if ($support.canvas && $support.dataURL) {
if (typeof canvas == "string") { canvas = document.getElementById(canvas); }
if (type == undefined) { type = 'png'; }
type = fixType(type);
if (/bmp/.test(type)) {
var data = getImageData(scaleCanvas(canvas, width, height));
var strData = genBitmapImage(data);
saveFile(makeURI(strData, downloadMime));
} else {
var strData = getDataURL(canvas, type, width, height);
saveFile(strData.replace(type, downloadMime));
}
}
};
var convertToImage = function (canvas, width, height, type) {
if ($support.canvas && $support.dataURL) {
if (typeof canvas == "string") { canvas = document.getElementById(canvas); }
if (type == undefined) { type = 'png'; }
type = fixType(type);
if (/bmp/.test(type)) {
var data = getImageData(scaleCanvas(canvas, width, height));
var strData = genBitmapImage(data);
return genImage(makeURI(strData, 'image/bmp'));
} else {
var strData = getDataURL(canvas, type, width, height);
return genImage(strData);
}
}
};
return {
saveAsImage: saveAsImage,
saveAsPNG: function (canvas, width, height) {
return saveAsImage(canvas, width, height, 'png');
},
saveAsJPEG: function (canvas, width, height) {
return saveAsImage(canvas, width, height, 'jpeg');
},
saveAsGIF: function (canvas, width, height) {
return saveAsImage(canvas, width, height, 'gif');
},
saveAsBMP: function (canvas, width, height) {
return saveAsImage(canvas, width, height, 'bmp');
},
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');
}
};
}();完整的一个代码案例：
完整的一个代码案例：
canvas生成图片
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
细化的一个代码部分
css
#demo{
background-color: #fff;
}
.red{
background-color: red;
width: 50px;
height: 50px;
}html
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
如果原来使用百分比设置元素宽高，请更改为px为单位的宽高，避免样式二次计算导致的模糊
js
上述代码中，通过设置canvas的容器为设备 的PixelRatio倍，再将canvas画布缩放，来尽量保证截图的清晰度。
可用参数
| 参数名称 | 类型 | 默认值 | 描述 |
|---|---|---|---|
| allowTaint | boolean | false | Whether to allow cross-origin images to taint the canvas---允许跨域 |
| background | string | #fff | Canvas background color, if none is specified in DOM. Set undefined for transparent---canvas的背景颜色，如果没有设定默认透明 |
| height | number | null | Define the heigt of the canvas in pixels. If null, renders with full height of the window.---canvas高度设定 |
| letterRendering | boolean | false | Whether to render each letter seperately. Necessary if letter-spacing is used.---在设置了字间距的时候有用 |
| logging | boolean | false | Whether to log events in the console.---在console.log()中输出信息 |
| proxy | string | undefined | Url to the proxy which is to be used for loading cross-origin images. If left empty, cross-origin images won't be loaded.---代理地址 |
| taintTest | boolean | true | Whether to test each image if it taints the canvas before drawing them---是否在渲染前测试图片 |
| timeout | number | 0 | Timeout for loading images, in milliseconds. Setting it to 0 will result in no timeout.---图片加载延迟，默认延迟为0，单位毫秒 |
| width | number | null | Define the width of the canvas in pixels. If null, renders with full width of the window.---canvas宽度 |
| useCORS | boolean | false | Whether to attempt to load cross-origin images as CORS served, before reverting back to proxy--这个我也不知道是干嘛的 |
html2canvas example