picture-crop-demo
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/index.html
前言
- vue版本：2.6.10 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/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
cropper.two.vue组件：https://github.com/MY729/picture-crop-demo/blob/master/src/components/cropper.two.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：
- 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/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()
}可以直接clone项目，本地运行查看代码和效果
Project setup
yarn install
Compiles and hot-reloads for development
yarn run serve
Compiles and minifies for production
yarn run build
Lints and fixes files
yarn run lint