Blob/DataURL/canvas/image的相互转换

// canvas转dataURL：canvas对象、转换格式、图像品质

function canvasToDataURL(canvas, format, quality){

return canvas.toDataURL(format||'image/jpeg', quality||1.0);

}

// DataURL转canvas

function dataURLToCanvas(dataurl, cb){

var canvas = document.createElement('CANVAS');

var ctx = canvas.getContext('2d');

var img = new Image();

img.onload = function(){

canvas.width = img.width;

canvas.height = img.height;

ctx.drawImage(img, 0, 0);

cb(canvas);

};

img.src = dataurl;

}

/*-----------------------------------------------------------------------*/

// image转canvas：图片地址

function imageToCanvas(src, cb){

var canvas = document.createElement('CANVAS');

var ctx = canvas.getContext('2d');

var img = new Image();

img.src = src;

img.onload = function (){

canvas.width = img.width;

canvas.height = img.height;

ctx.drawImage(img, 0, 0);

cb(canvas);

};

}

// canvas转image

function canvasToImage(canvas){

var img = new Image();

img.src = canvas.toDataURL('image/jpeg', 1.0);

return img;

}

/*-----------------------------------------------------------------------*/

// File/Blob对象转DataURL

function fileOrBlobToDataURL(obj, cb){

var a = new FileReader();

a.readAsDataURL(obj);

a.onload = function (e){

cb(e.target.result);

};

}

// DataURL转Blob对象

function dataURLToBlob(dataurl){

var arr = dataurl.split(',');

var mime = arr[0].match(/:(.*?);/)[1];

var bstr = atob(arr[1]);

var n = bstr.length;

var u8arr = new Uint8Array(n);

while(n--){

u8arr[n] = bstr.charCodeAt(n);

}

return new Blob([u8arr], {type:mime});

}

/*-----------------------------------------------------------------------*/

// Blob转image

function blobToImage(blob, cb){

fileOrBlobToDataURL(blob, function (dataurl){

var img = new Image();

img.src = dataurl;

cb(img);

});

}

// image转Blob

function imageToBlob(src, cb){

imageToCanvas(src, function (canvas){

cb(dataURLToBlob(canvasToDataURL(canvas)));

});

}

/*-----------------------------------------------------------------------*/

// Blob转canvas

function BlobToCanvas(blob, cb){

fileOrBlobToDataURL(blob, function (dataurl){

dataURLToCanvas(dataurl, cb);

});

}

// canvas转Blob

function canvasToBlob(canvas, cb){

cb(dataURLToBlob(canvasToDataURL(canvas)));

}

/*-----------------------------------------------------------------------*/

// image转dataURL

function imageToDataURL(src, cb){

imageToCanvas(src, function (canvas){

cb(canvasToDataURL(canvas));

});

}

// dataURL转image，这个不需要转，直接给了src就能用

function dataURLToImage(dataurl){

var img = new Image();

img.src = d;

return img;

}