Use vue+ html2Canvas +exif-js github address online demo

The main function

  • To upload pictures
  • Perform operations on the picture: move, zoom in, zoom out
  • Synthesis of posters

Specific functions:

To upload pictures

html:

<input type="file" value="" accept="image/*" @click="getPhoto" id="image-input">
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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() { // Get the image data
                Exif.getAllTags(this); // Get all the data of the image. The value is returned as an object
                orientation = Exif.getTag(this."Orientation"); // Get the direction of the image
                var rotateCanvas = document.createElement("canvas"),
                rotateCtx = rotateCanvas.getContext("2d");
                 // For image direction processing
                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 : // Clockwise 90 degrees
                        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 degrees
                        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); }); })})})}Copy the code

Moving pictures

Bind the picture and frame to @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
},
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Synthetic images

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('Please upload picture')}}Copy the code

Problems encountered

  1. – preventing zooming issues on browsers using event.preventDefault() on tounchMove
  2. Scale = window. DevicePixelRatio when html2Canvas writes parameters
  3. The judgment of distance when zooming a picture

    Two cases need to be distinguished:
    • Two fingers zoom
    • A condition in which one hand lets go and the other continues after scaling. So there’s still an element in e.Touches on touchEnd. So there’s a judgment to be made here.
  4. Vue :style=” inline style 
    :style="{transform:'scale('+ myImg.scale+ ') translate('+myImg.position.x+'px,'+myImg.position.y+'px)'}"
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