canvas转img，blob相互转换

摘自：https://www.cnblogs.com/jyuf/p/7251591.html

 

 

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;
}
/*-----------------------------------------------------------------------*/