土旦：移動端 Vue+Vant 的Uploader 實現 ：上傳、壓縮、旋轉圖片

面向百度開發

html

 <van-uploader :after-read="onRead" accept="image/*">
        <img src="./icon_input_add.png" />
 </van-uploader>

 

js

data() {
        return {
            files: {
                name: "",
                type: ""
            },
            headerImage: null,
            picValue: null,
            upImgUrl,
        }
    },
    // 組件方法 獲取 流
    async onRead(file) {
            // console.log(file);
            // console.log(file.file);
            this.files.name = file.file.name; // 獲取文件名
            this.files.type = file.file.type; // 獲取類型
            this.picValue = file.file; // 文件流
            this.imgPreview(this.picValue);
        },
        // 處理圖片
        imgPreview(file) {
            let self = this;
            let Orientation;
            //去獲取拍照時的信息，解決拍出來的照片旋轉問題
            Exif.getData(file, function () {
                Orientation = Exif.getTag(this, "Orientation");
            });
            // 看支持不支持FileReader
            if (!file || !window.FileReader) return;
            if (/^image/.test(file.type)) {
                // 創建一個reader
                let reader = new FileReader();
                // 將圖片2將轉成 base64 格式
                reader.readAsDataURL(file);
                // 讀取成功后的回調
                reader.onloadend = function () {
                    // console.log(this.result);
                    let result = this.result;
                    let img = new Image();
                    img.src = result;
                    //判斷圖片是否大於500K,是就直接上傳，反之壓縮圖片
                    if (this.result.length <= 500 * 1024) {
                        self.headerImage = this.result;
                        self.postImg();
                    } else {
                        img.onload = function () {
                            let data = self.compress(img, Orientation);
                            self.headerImage = data;
                            self.postImg();
                        };
                    }
                };
            }
        },
        // 壓縮圖片
        compress(img, Orientation) {
            let canvas = document.createElement("canvas");
            let ctx = canvas.getContext("2d");
            //瓦片canvas
            let tCanvas = document.createElement("canvas");
            let tctx = tCanvas.getContext("2d");
            // let initSize = img.src.length;
            let width = img.width;
            let height = img.height;
            //如果圖片大於四百萬像素，計算壓縮比並將大小壓至400萬以下
            let ratio;
            if ((ratio = (width * height) / 4000000) > 1) {
                // console.log("大於400萬像素");
                ratio = Math.sqrt(ratio);
                width /= ratio;
                height /= ratio;
            } else {
                ratio = 1;
            }
            canvas.width = width;
            canvas.height = height;
            //        鋪底色
            ctx.fillStyle = "#fff";
            ctx.fillRect(0, 0, canvas.width, canvas.height);
            //如果圖片像素大於100萬則使用瓦片繪制
            let count;
            if ((count = (width * height) / 1000000) > 1) {
                // console.log("超過100W像素");
                count = ~~(Math.sqrt(count) + 1); //計算要分成多少塊瓦片
                //            計算每塊瓦片的寬和高
                let nw = ~~(width / count);
                let nh = ~~(height / count);
                tCanvas.width = nw;
                tCanvas.height = nh;
                for (let i = 0; i < count; i++) {
                    for (let j = 0; j < count; j++) {
                        tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
                        ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
                    }
                }
            } else {
                ctx.drawImage(img, 0, 0, width, height);
            }
            //修復ios上傳圖片的時候 被旋轉的問題
            if (Orientation != "" && Orientation != 1) {
                switch (Orientation) {
                    case 6: //需要順時針（向左）90度旋轉
                        this.rotateImg(img, "left", canvas);
                        break;
                    case 8: //需要逆時針（向右）90度旋轉
                        this.rotateImg(img, "right", canvas);
                        break;
                    case 3: //需要180度旋轉
                        this.rotateImg(img, "right", canvas); //轉兩次
                        this.rotateImg(img, "right", canvas);
                        break;
                }
            }
            //進行最小壓縮
            let ndata = canvas.toDataURL("image/jpeg", 0.1);
            tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
            return ndata;
        },
        // 旋轉圖片
        rotateImg(img, direction, canvas) {
            //最小與最大旋轉方向，圖片旋轉4次后回到原方向
            const min_step = 0;
            const max_step = 3;
            if (img == null) return;
            //img的高度和寬度不能在img元素隱藏后獲取，否則會出錯
            let height = img.height;
            let width = img.width;
            let step = 2;
            if (step == null) {
                step = min_step;
            }
            if (direction == "right") {
                step++;
                //旋轉到原位置，即超過最大值
                step > max_step && (step = min_step);
            } else {
                step--;
                step < min_step && (step = max_step);
            }
            //旋轉角度以弧度值為參數
            let degree = (step * 90 * Math.PI) / 180;
            let ctx = canvas.getContext("2d");
            switch (step) {
                case 0:
                    canvas.width = width;
                    canvas.height = height;
                    ctx.drawImage(img, 0, 0);
                    break;
                case 1:
                    canvas.width = height;
                    canvas.height = width;
                    ctx.rotate(degree);
                    ctx.drawImage(img, 0, -height);
                    break;
                case 2:
                    canvas.width = width;
                    canvas.height = height;
                    ctx.rotate(degree);
                    ctx.drawImage(img, -width, -height);
                    break;
                case 3:
                    canvas.width = height;
                    canvas.height = width;
                    ctx.rotate(degree);
                    ctx.drawImage(img, -width, 0);
                    break;
            }
        },
        //將base64轉換為文件
        dataURLtoFile(dataurl) {
            var arr = dataurl.split(","),
                bstr = atob(arr[1]),
                n = bstr.length,
                u8arr = new Uint8Array(n);
            while (n--) {
                u8arr[n] = bstr.charCodeAt(n);
            }
            return new File([u8arr], this.files.name, {
                type: this.files.type
            });
        },
        //這里寫接口 
        async postImg() {
            let file = this.dataURLtoFile(this.headerImage);
            let formData = new window.FormData();
            formData.append("file", file);
            toast_loding(this, "圖片上傳中···");
            try {
                let res = await util.ajax.post(this.upImgUrl, formData, {
                    headers: {
                        "Content-Type": "multipart/form-data"
                    }
                });
            } catch (e) {
                console.log(e);
            }
        }

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參考：https://www.cnblogs.com/lvshaonan/p/8547676.html