/**
 * @description 将图片的base64 转变成Blob形式
 * */
function dataURLtoBlob(dataurl) {
    let arr = dataurl.split(',')
    let mime = arr[0].match(/:(.*?);/)[1]

    let bstr = atob(arr[1])
    let n = bstr.length
    let u8arr = new Uint8Array(n)
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n)
    }
    return new Blob([u8arr], { type: mime })
}

/**
 * @description 使用canvas绘制缩略图
 * */
export const getImageByCanvas = function(url, callback) {
    getThumb(url, dataURL => {
        callback(window.URL.createObjectURL(dataURLtoBlob(dataURL)))
    })
}