Blob/DataURL/canvas/image的相互转换

函数都比较简单，直接看就ok了
 
/*-----------------------------------------------------------------------*/
// 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;
}
/*-----------------------------------------------------------------------*/