cc/web/src/utils/image.js

export default class ImageCompress {
    constructor(file, fileSize, maxWH = 1920) {
        this.file = file
        this.fileSize = fileSize
        this.maxWH = maxWH // 最大长宽
    }

    compress() {
        // 压缩
        const fileType = this.file.type
        const fileSize = this.file.size / 1024
        return new Promise(resolve => {
            const reader = new FileReader();
            reader.readAsDataURL(this.file);
            reader.onload = () => {
                const canvas = document.createElement('canvas');
                const img = document.createElement('img');
                img.src = reader.result;
                img.onload = () => {
                    const ctx = canvas.getContext('2d');
                    let _dWH = this.dWH(img.width, img.height, this.maxWH)
                    canvas.width = _dWH.width
                    canvas.height = _dWH.height

                    // 清空后, 重写画布
                    ctx.clearRect(0, 0, canvas.width, canvas.height)
                    ctx.drawImage(img, 0, 0, canvas.width, canvas.height)

                    let newImgData = canvas.toDataURL(fileType, 0.90)

                    // 压缩宽高后的图像大小
                    let newImgSize = this.fileSizeKB(newImgData)

                    if (newImgSize > this.fileSize) {
                        console.log('图片尺寸太大!' + fileSize + " >> " + newImgSize)
                        reject(`图片尺寸太大!`)
                    }

                    let blob = this.dataURLtoBlob(newImgData, fileType)
                    let nfile = new File([blob], this.file.name);
                    resolve(nfile)
                };
            };
        });
    }

    /*
     * 长宽等比缩小
     * 图像的一边(长或宽)为最大目标值
     * */
    dWH(srcW, srcH, dMax) {

        let defaults = {
            width: srcW,
            height: srcH
        }
        if (Math.max(srcW, srcH) > dMax) {
            if (srcW > srcH) {
                defaults.width = dMax
                defaults.height = Math.round(srcH * (dMax / srcW))
                return defaults
            } else {
                defaults.height = dMax
                defaults.width = Math.round(srcW * (dMax / srcH))
                return defaults
            }
        } else {
            return defaults
        }
    }

    fileSizeKB(dataURL) {
        let self = this

        let sizeKB = 0
        sizeKB = Math.round((dataURL.split(',')[1].length * 3 / 4) / 1024)
        return sizeKB
    }

    /*
     * 转为Blob
     * */
    dataURLtoBlob(dataURL, fileType) {
        let self = this

        let byteString = atob(dataURL.split(',')[1])
        let mimeString = dataURL.split(',')[0].split(':')[1].split(';')[0]
        let ab = new ArrayBuffer(byteString.length)
        let ia = new Uint8Array(ab)
        for (let i = 0; i < byteString.length; i++) {
            ia[i] = byteString.charCodeAt(i)
        }
        if (fileType) {
            mimeString = fileType
        }
        return new Blob([ab], { type: mimeString, lastModifiedDate: new Date() })
    }

}