摘要：所以需要在這里做一個判斷。使用的內聯樣式時遇上的寫法問題直接使用手機拍照得到的圖片方向有問題

原文鏈接：鏈接描述
使用vue+html2canvas+exif-js
github地址
線上demo

上傳圖片

對圖片進行操作：移動、放大、縮小

合成海報

html:

js

getPhoto () {
    var imageInput = document.querySelector("#image-input")
    var that = this
    imageInput.addEventListener("change", function (e) {
        reads = new FileReader()
        reads.readAsDataURL(this.files[0])
        reads.addEventListener("load", function (e) {
            that.imgUrl = this.result
            that.myImg.position.x = 0
            that.myImg.position.y = 0
            that.myImg.scale = 1
            var orientation
            that.previewImg.addEventListener("load", function () {
                Exif.getData(that.previewImg, function() { // 獲取圖像的數據
                Exif.getAllTags(this); // 獲取圖像的全部數據，值以對象的方式返回
                orientation = Exif.getTag(this, "Orientation"); // 獲取圖像的拍攝方向
                var rotateCanvas = document.createElement("canvas"),
                rotateCtx = rotateCanvas.getContext("2d");
                 // 針對圖像方向進行處理
                switch (orientation) {
                    case 1 :
                        rotateCanvas.width = that.previewImg.width;
                        rotateCanvas.height = that.previewImg.height;
                        rotateCtx.drawImage(that.previewImg, 0, 0, that.previewImg.width, that.previewImg.height);
                        break;
                    case 6 : // 順時針 90 度
                        rotateCanvas.width = that.previewImg.height;
                        rotateCanvas.height = that.previewImg.width;
                        rotateCtx.translate(0, 0);
                        rotateCtx.rotate(90 * Math.PI / 180);
                        rotateCtx.drawImage(that.previewImg, 0, -that.previewImg.height, that.previewImg.width, that.previewImg.height);
                        break;
                    case 8 :
                        rotateCanvas.width = that.previewImg.height;
                        rotateCanvas.height = that.previewImg.width;
                        rotateCtx.translate(0, 0);
                        rotateCtx.rotate(-90 * Math.PI / 180);
                        rotateCtx.drawImage(that.previewImg, -that.previewImg.width, 0, that.previewImg.width, that.previewImg.height);
                        break;
                    case 3 : // 180 度
                        rotateCanvas.width = that.previewImg.width;
                        rotateCanvas.height = that.previewImg.height;
                        rotateCtx.translate(0, 0);
                        rotateCtx.rotate(Math.PI);
                        rotateCtx.drawImage(that.previewImg, -that.previewImg.width, -that.previewImg.height, that.previewImg.width, that.previewImg.height);
                        break;
                    default :
                        rotateCanvas.width = that.previewImg.width;
                        rotateCanvas.height = that.previewImg.height;
                        rotateCtx.drawImage(that.previewImg, 0, 0, that.previewImg.width, that.previewImg.height);
                    }
                    var rotateBase64 = rotateCanvas.toDataURL("image/jpeg", 0.5);
                });
            })
        }) 
    })
}

對圖片和相框綁定@touchstart @touchmove @touchend

getInitPosition (e) {
    event.preventDefault()
    if (this.imgUrl) {
        var length = e.touches.length
         if (length > 1) {
            let pointOne = e.touches[0]
            let pointTwo = e.touches[1]
            this.initTouchX = pointOne.clientX - pointTwo.clientX
            this.initTouchY = pointOne.clientY - pointTwo.clientY
        } else {
            var touches = e.touches[0]
            this.initTouchX = touches.clientX
            this.initTouchY = touches.clientY
        }   
    }
},
 getMovePosition (e) {
    event.preventDefault()
    if (this.imgUrl) {
        var length = e.touches.length
        if (length > 1) {
            let pointOne = e.touches[0]
            let pointTwo = e.touches[1]
            this.changeTouchX = pointOne.clientX - pointTwo.clientX
            this.changeTouchY = pointOne.clientY - pointTwo.clientY
            var scale = (this.changeTouchX - this.initTouchX) > (this.changeTouchY - this.initTouchY) ? (this.changeTouchX / this.initTouchX) : (this.changeTouchY / this.initTouchY) 
            scale *= this.myImg.lastScale
            this.myImg.scale = scale > 3 ? 3 : scale < 0.5 ? 0.5 : scale
        } else {
            var touches = e.touches[0]
            this.changeTouchX = touches.clientX - this.initTouchX
            this.changeTouchY = touches.clientY - this.initTouchY
            this.myImg.position.x = this.lastTouchX + (this.changeTouchX / this.myImg.scale)
            this.myImg.position.y = this.lastTouchY + (this.changeTouchY / this.myImg.scale)
        }   
    }
},
getLeavePosition (e) {
    this.myImg.lastScale = this.myImg.scale
    if (e.touches.length > 0) {
        var touches = e.touches[0]
        this.initTouchX = touches.clientX
        this.initTouchY = touches.clientY
    }
    this.lastTouchX = this.myImg.position.x
    this.lastTouchY = this.myImg.position.y
},

createPhoto () {
    if (this.imgUrl) {
        let photoBox = document.querySelector(".photo-box")
        newImgWidth = photoBox.style.offsetWidth
        let newImgHeight = photoBox.style.offsetHeight
        let scale = window.devicePixelRatio
        let that = this
        html2canvas(photoBox, {
            width: newImgWidth,
            height: newImgHeight,
            scale: scale,
            useCORS: true
        }).then(function (canvas) { 
            var dataUrl = canvas.toDataURL("image/jpg")
            localStorage.imgData = dataUrl
            that.$router.push({
                name: "share",
                params: {
                    storage: "imgData"
                }
            })
        })
    } else {
        alert("請上傳圖片")
    }
}

1) 在瀏覽器上阻止縮放的問題

在tounchmove時使用event.preventDefault()

2) 合成圖片的清晰度

在html2canvas寫參數時，scale = window.devicePixelRatio

3) 對圖片進行縮放時，對距離的判斷

這里需要區分兩種情況：
- 兩指縮放
- 一指移動  
在兩指縮放后會有一個手放手另一個手繼續操作的情況。這樣在touchend時，e.touches還存在一個元素。所以需要在這里做一個判斷。

4) 使用vue的:style="內聯樣式"時遇上的寫法問題

:style="{transform:"scale("+ myImg.scale+ ") translate("+myImg.position.x+"px,"+myImg.position.y+"px)"}"

5）直接使用手機拍照得到的圖片方向有問題