前端图片转换的几种方式-back

/*
 * @Author: your name
 * @Date: 2020-09-04 18:38:23
 * @LastEditTime: 2021-05-07 15:12:14
 * @LastEditors: Please set LastEditors
 * @Description: In User Settings Edit
 * @FilePath: \tt-desktop\src\renderer\utils\imgFormatConversion.js
 */
// base64转换为blob对象
export function dataURLtoBlob(dataurl) {
    var arr = dataurl.split(','),
        mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], { type: mime });
}

export function dataURLtoFile(dataurl) {
    let blob = dataURLtoBlob(dataurl);
    return new File(
        [blob],
        dataurl.substring(25, 40), { type: blob.type }
    );

}
// 获取base64图片的宽与高
export function Base64WidthAndHeight(base64) {
    return new Promise((resolve, reject) => {
        var img = new Image()
        img.src = `${base64}`
        img.onload = () => {
            resolve({
                width: img.width,
                height: img.height
            })
        }
        img.onerror = error => reject(error)
    })
}

//file对象转化为buffer对象
export function fileToBuf(file) {
    return new Promise((resolve, reject) => {
        const reader = new FileReader()
        const filename = file.name;
        reader.readAsArrayBuffer(file)
        reader.onload = () => {
            resolve(Buffer.from(reader.result))
        }
        reader.onerror = error => reject(error)
    })
}


// file对象转换为base64,去掉了data:image\/png;base64,
export function toBase64(file) {
    return new Promise((resolve, reject) => {
        const reader = new FileReader()
        reader.readAsDataURL(file)
        reader.onload = () => {
            resolve(reader.result.split('base64,')[1])
        }
        reader.onerror = error => reject(error)
    })
}
//base64转压缩
export function toSmallBase64(elementObj, maxWidth, maxHeight) {
    return new Promise((resolve, reject) => {
        if (typeof(FileReader) === 'undefined') {
            myApp.log.error("抱歉，你的浏览器不支持发送图片,不支持使用FileReader");
        } else {
            try {
                //创建一个img对象
                var img = new Image();
                img.src = elementObj;
                // base64地址图片加载完毕后执行
                img.onload = function() {
                    // 缩放图片需要的canvas（也可以在DOM中直接定义canvas标签，这样就能把压缩完的图片不转base64也能直接显示出来）
                    var canvas = document.createElement('canvas');
                    var context = canvas.getContext('2d');
                    // 图片原始尺寸
                    var originWidth = this.width;
                    var originHeight = this.height;
                    // 最大尺寸限制，可通过设置宽高来实现图片压缩程度
                    //var maxWidth = 500;
                    //var maxHeight = 400;
                    // 目标尺寸
                    var targetWidth = originWidth,
                        targetHeight = originHeight;
                    // 图片尺寸超过最大值的限制
                    if (originWidth > maxWidth || originHeight > maxHeight) {
                        if (originWidth / originHeight > maxWidth / maxHeight) {
                            // 更宽，按照宽度限定尺寸
                            targetWidth = maxWidth;
                            targetHeight = Math.round(maxWidth * (originHeight / originWidth));
                        } else {
                            targetHeight = maxHeight;
                            targetWidth = Math.round(maxHeight * (originWidth / originHeight));
                        }
                    }
                    // canvas对图片进行缩放
                    canvas.width = targetWidth;
                    canvas.height = targetHeight;
                    // 清除画布
                    context.clearRect(0, 0, targetWidth, targetHeight);
                    // 图片压缩
                    /*第一个参数是创建的img对象；第二三个参数是左上角坐标，后面两个是画布区域宽高*/
                    context.drawImage(img, 0, 0, targetWidth, targetHeight);
                    //压缩后的图片转base64 url
                    //canvas.toDataURL(mimeType, qualityArgument),mimeType 默认值是'image/png';
                    //qualityArgument表示导出的图片质量，只有导出为jpeg和webp格式的时候此参数才有效，默认值是0.92
                    var base64_url = canvas.toDataURL('image/jpeg', 0.92); //base64 格式
                    resolve(base64_url)
                }
            } catch (e) {
                reject('图片转Base64出错啦！' + e.toString())
            }
        }
    })

}
//网络图片转化为base64
export function getBase64Image(img) {
    let canvas = document.createElement("canvas")
    canvas.width = img.width
    canvas.height = img.height
    let ctx = canvas.getContext("2d")
    ctx.drawImage(img, 0, 0, img.width, img.height)
    let ext = img.src.substring(img.src.lastIndexOf(".") + 1).toLowerCase()
    let dataURL = canvas.toDataURL("image/" + ext)
    return dataURL
}
export function srcToBaseOrFile(src, isFile) {
    let image = new Image()
    image.src = src
    image.setAttribute("crossOrigin", "Anonymous")
    // image.setAttribute("crossorigin", " *")
    image.onload = function() {
        let base64 = getBase64Image(image)
        if (isFile) {
            let formData = new FormData()
            //转换base64到file
            let file = baseToFile(base64, "test")
            formData.append("imageName", file)
        }
    }
}
export function baseToFile(data, fileName) {
    const dataArr = data.split(",")
    const byteString = atob(dataArr[1])

    const options = {
        type: "image/jpeg",
        endings: "native"
    }
    const u8Arr = new Uint8Array(byteString.length)
    for (let i = 0; i < byteString.length; i++) {
        u8Arr[i] = byteString.charCodeAt(i)
    }
    return new File([u8Arr], fileName + ".jpg", options)
}


// 本地图片转为base64
export function locationPcitionToBase(fileUrl) {
    const fs = require('fs')
    let imageData = fs.readFileSync(fileUrl); // 例：fileUrl="D:\\test\\test.bmp"
    let imageBase64 = imageData.toString("base64");
    let imagePrefix = "data:image/bmp;base64,";
    return imageBase64;
}