详解vue项目中实现图片裁剪功能

演示地址

https://my729.github.io/picture-crop-demo/dist/#/

前言

使用 cropperjs插件 和 原生canvas 两种方式实现图片裁剪功能

使用cropperjs插件

安装cropperjs

yarn install cropperjs

初始化一个canvas元素，并在上面绘制图片

<canvas :id="data.src" ref="canvas"></canvas>

// 在canvas上绘制图片
drawImg () {
 this.$nextTick(() => {
 // 获取canvas节点
 let canvas = document.getElementById(this.data.src)
 if (canvas) {
 // 设置canvas的宽为canvas的父元素宽度，宽高比3:2
 let parentEle = canvas.parentElement
 canvas.width = parentEle.offsetWidth
 canvas.height = 2 * parentEle.offsetWidth / 3
 let ctx = canvas.getContext('2d')
 ctx.clearRect(0, 0, canvas.width, canvas.height)
 let img = new Image()
 img.crossOrigin = 'Anonymous'
 img.src = this.data.src
 img.onload = function () {
 ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
 }
 }
 })
}

如果遇到canvas跨域绘制图片报错，设置图片img.crossOrigin = 'Anonymous'，并且服务器响应头设置Access-Control-Allow-Origin：*

创建cropperjs

// 引入
import Cropper from 'cropperjs'

// 显示裁剪框
initCropper () {
 let cropper = new Cropper(this.$refs.canvas, {
 checkCrossOrigin: true,
 viewMode: 2,
 aspectRatio: 3 / 2
 })
}

更多方法和属性，参考官网： https://github.com/fengyuanchen/cropperjs

具体实现，可以查看源码的cropper.vue 或 cropper.one.vue组件:

cropper.vue组件：https://github.com/MY729/picture-crop-demo/blob/master/src/components/cropper.vue
cropper.one.vue组件：https://github.com/MY729/picture-crop-demo/blob/master/src/components/cropper.one.vue

使用canvas实现图片裁剪

支持鼠标绘制裁剪框，并移动裁剪框

思路：

canvas的isPointInPath()方法： 如果给定的点的坐标位于路径之内的话（包括路径的边）,否则返回 false

具体实现可查看源码cropper.canvas.vue组件: https://github.com/MY729/picture-crop-demo/blob/master/src/components/cropper.canvas.vue

cropImg () {
 let canvas = document.getElementById(this.data.img_url)
 let ctx = canvas.getContext('2d')
 let img = new Image()
 img.onload = function () {
 ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
 }
 img.src = this.data.src
 let drag = false // 是否拖动矩形
 let flag = false // 是否绘制矩形
 let rectWidth = 0 // 绘制矩形的宽
 let rectHeight = 0 // 绘制矩形的高
 let clickX = 0 // 矩形开始绘制X坐标
 let clickY = 0 // 矩形开始绘制Y坐标
 let dragX = 0 // 当要拖动矩形点击时X坐标
 let dragY = 0 // 当要拖动矩形点击时Y坐标
 let newRectX = 0 // 拖动变化后矩形开始绘制的X坐标
 let newRectY = 0 // 拖动变化后矩形开始绘制的Y坐标
 // 鼠标按下
 canvas.onmousedown = e => {
 // 每次点击前如果有绘制好的矩形框，通过路径绘制出来，用于下面的判断
 ctx.beginPath()
 ctx.setLineDash([6, 6])
 ctx.moveTo(newRectX, newRectY)
 ctx.lineTo(newRectX + rectWidth, newRectY)
 ctx.lineTo(newRectX + rectWidth, newRectY + rectHeight)
 ctx.lineTo(newRectX, newRectY + rectHeight)
 ctx.lineTo(newRectX, newRectY)
 ctx.strokeStyle = 'green'
 ctx.stroke()
 // 每次点击，通过判断鼠标点击的点在矩形框内还是外，来决定重新绘制还是移动矩形框
 if (ctx.isPointInPath(e.offsetX, e.offsetY)) {
 drag = true
 dragX = e.offsetX
 dragY = e.offsetY
 clickX = newRectX
 clickY = newRectY
 } else {
 ctx.clearRect(0, 0, canvas.width, canvas.height)
 ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
 flag = true
 clickX = e.offsetX
 clickY = e.offsetY
 newRectX = e.offsetX
 newRectY = e.offsetY
 }
 }
 // 鼠标抬起
 canvas.onmouseup = () => {
 if (flag) {
 flag = false
 this.sureCrop(clickX, clickY, rectWidth, rectHeight)
 }
 if (drag) {
 drag = false
 this.sureCrop(newRectX, newRectY, rectWidth, rectHeight)
 }
 }
 // 鼠标移动
 canvas.onmousemove = (e) => {
 if (flag) {
 ctx.clearRect(0, 0, canvas.width, canvas.height)
 ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
 rectWidth = e.offsetX - clickX
 rectHeight = e.offsetY - clickY

 ctx.beginPath()
 ctx.strokeStyle = '#FF0000'
 ctx.strokeRect(clickX, clickY, rectWidth, rectHeight)
 ctx.closePath()
 }
 if (drag) {
 ctx.clearRect(0, 0, canvas.width, canvas.height)
 ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
 ctx.beginPath()
 newRectX = clickX + e.offsetX - dragX
 newRectY = clickY + e.offsetY - dragY
 ctx.strokeStyle = 'yellow'
 ctx.strokeRect(newRectX, newRectY, rectWidth, rectHeight)
 ctx.closePath()
 }
 }
},
// 拿到裁剪后的参数，可自行处理图片
sureCrop (x, y, width, height) {
 let canvas = document.getElementById(this.data.img_url + 'after')
 // 设置canvas的宽为canvas的父元素宽度，宽高比3:2
 let parentEle = canvas.parentElement
 canvas.width = parentEle.offsetWidth
 canvas.height = 2 * parentEle.offsetWidth / 3
 let ctx = canvas.getContext('2d')
 let img = new Image()
 img.src = this.data.src
 img.onload = function () {
 ctx.beginPath()
 ctx.moveTo(x, y)
 ctx.lineTo(x + width, y)
 ctx.lineTo(x + width, y + height)
 ctx.lineTo(x, y + height)
 ctx.clip()
 ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
 }
 ctx.stroke()
}

源码地址

https://github.com/MY729/picture-crop-demo

可以直接clone项目，本地运行查看代码和效果

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