原文地址

https://github.com/MY729/pict…

在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

• vue版本：3.6.3 https://cli.vuejs.org/zh/
• cropperjs: 1.5.1 https://github.com/fengyuanchen/cropperjs
• elementUI https://element.eleme.io/#/zh-CN

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/pict…
cropper.one.vue组件：https://github.com/MY729/pict…

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：

• 在canvas上绘制图片为背景
• 监听鼠标点击、移动、松开事件

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/pict…

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/pict…

可以直接clone项目，本地运行查看代码和效果