使用canvas一步步实现图片打码功能的方法

2024-09-05 07:22:54

字体：大中小

来源：转载

供稿：网友

原文地址
https://github.com/MY729/front-common-funtion/blob/master/picture-code-demo/README.md

预览地址
https://my729.github.io/front-common-funtion/picture-code-demo/picture-code.html

准备工作

demo 基于 vue + elelment-ui

首先创建一个html文件, 并引入 vue 和 elelment-ui(注意还有样式文件)

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <meta name="viewport" content="width=device-width, initial-scale=1.0">  <meta http-equiv="X-UA-Compatible" content="ie=edge">  <title>Document</title>  <!-- elelment-ui样式 -->  <link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css"></head><body>  </body><!-- 引入vue --><script src="https://cdn.jsdelivr.net/npm/vue"></script><!-- 引入element-ui --><script src="https://unpkg.com/element-ui/lib/index.js"></script></html>

接下来就可以写我们的打码功能啦

实现思路

创建canvas画布，并将要打码的图片绘制上去
监听鼠标在图片上的点击，移动、松开事件，在canvas画布上绘制要打码的区域
处理绘制的打码区域
保存打码后的图片

将要打码的图片绘制到canvas画布上

// 初始化 绘制图片toCode (currentImg) {  this.$nextTick(() => {    // 获取将要绘制的canvas的父元素节点    let parentId = document.getElementById('parentId')    // 初始化图片    let drawImg = new Image()    drawImg.setAttribute('crossOrigin', 'anonymous')    drawImg.crossOrigin = 'Anonymous'    drawImg.src = currentImg    // 创建canvas元素并添加到父节点中    let addCanvas = document.createElement('canvas')    parentId.appendChild(addCanvas)    let canvas = parentId.lastElementChild    canvas.id = 'imgCanvas'    if (canvas.getContext) {      let ctx = canvas.getContext('2d')      // 绘制图片      drawImg.onload = function () {        canvas.width = 720        canvas.height = 500        ctx.drawImage(drawImg, 0, 0, 720, 500)      }    }  })}

点击打码按钮，绘制打码区域

思路：

鼠标点击，获取点击时的坐标，每次点击前可能会存在打过码的区域，先清除画布，重新绘制图片
鼠标移动，开始绘制打码的矩形，通过移动的坐标和上面点击的点坐标确定绘制的矩形坐标和宽高
将绘制的打码矩形，分割成一个个宽高15像素的小正方形，并给每个小正方形生产随机颜色
鼠标松开，停止绘制矩形

// 打码dialogCode (img) {  let parentId = document.getElementById('parentId')  let canvas = document.getElementById('imgCanvas')  if (canvas.getContext) {    let ctx = canvas.getContext('2d')    let drawImage = new Image()    drawImage.crossOrigin = 'Anonymous'    drawImage.src = img    drawImage.onload = () => {      ctx.drawImage(drawImage, 0, 0, 720, 500)    }    // 鼠标点击    parentId.onmousedown = e => {      ctx.clearRect(0, 0, canvas.width, canvas.height)      ctx.drawImage(drawImage, 0, 0, 720, 500)      this.flag = true      this.clickX = e.offsetX // 鼠标点击时的X      this.clickY = e.offsetY // 鼠标点击时的Y    }    // 鼠标松开    parentId.onmouseup = () => {      this.flag = false    }    // 鼠标按下    parentId.onmousemove = e => {      if (this.flag) {        ctx.clearRect(0, 0, canvas.width, canvas.height)        ctx.drawImage(drawImage, 0, 0, 720, 500)        ctx.beginPath()        let pixels = [] // 二维数组，每个子数组有5个值（绘制矩形左上角的X坐标、y坐标，矩形的宽、高，生成的4位随机数用于颜色值）        for (let x = 0; x < (e.offsetX - this.clickX) / 15; x++) {          for (let y = 0; y < (e.offsetY - this.clickY) / 15; y++) {            pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])          }          for (let y = 0; y > (e.offsetY - this.clickY) / 15; y--) {            pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])          }        }        for (let x = 0; x > (e.offsetX - this.clickX) / 15; x--) {          for (let y = 0; y > (e.offsetY - this.clickY) / 15; y--) {            pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])          }          for (let y = 0; y < (e.offsetY - this.clickY) / 15; y++) {            pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])          }        }        // 遍历数组绘制小正方形块        for (let i = 0; i < pixels.length; i++) {          ctx.fillStyle = '#bf' + pixels[i][4]          ctx.fillRect(pixels[i][0], pixels[i][1], pixels[i][2], pixels[i][3])        }        ctx.fill()        ctx.closePath()      }    }  }}

保存

// 保存dialogUpload () {  let canvas = document.getElementById('imgCanvas')  let tempImg = canvas.toDataURL('image/png')  let imgURL = document.getElementById('imgURL')  imgURL.crossOrigin = 'Anonymous'  imgURL.src = tempImg}

源码

复制到html文件可预览

<!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <meta name="viewport" content="width=device-width, initial-scale=1.0">  <meta http-equiv="X-UA-Compatible" content="ie=edge">  <title>使用canvas一步步实现图片打码功能</title>  <!-- elelment-ui样式 -->  <link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css">  <style type="text/css">    .rc-code__buttons {      margin: 20px;    }  </style></head><body>  <div id="app">    <div class="rc-code__buttons">      <h1>vue项目中使用canvas一步步实现图片打码功能</h1>      <el-button type="primary" @click="dialogCode(data.img_url)">打码</el-button>      <el-button type="success" @click="dialogUpload()">保存</el-button>    </div>    <el-row>      <el-col :span="12"><h3>点击打码按钮，在图片上绘制打码区域； 点击保存，生成打码后的图片</h3></el-col>      <el-col :span="12"><h3>保存后的图片</h3></el-col>      <el-col :span="12"><div id="parentId"></div></el-col>      <el-col :span="12"><img id="imgURL"/></el-col>    </el-row>  </div></body><!-- 引入vue --><script src="https://cdn.jsdelivr.net/npm/vue"></script><!-- 引入element-ui --><script src="https://unpkg.com/element-ui/lib/index.js"></script><script>new Vue({  el: '#app',  data () {    return {      data: {        img_url: 'https://avatars0.githubusercontent.com/u/26196557?s=460&v=4'      },      flag: false, // 是否绘制矩形      clickX: '', // 开始绘制矩形时，鼠标点击时的x坐标      clickY: '' // 开始绘制矩形时，鼠标点击时的y坐标    }  },  mounted() {    this.toCode(this.data.img_url)  },  methods: {    // 初始化 绘制图片    toCode (currentImg) {      this.$nextTick(() => {        let parentId = document.getElementById('parentId')        let drawImg = new Image()        drawImg.setAttribute('crossOrigin', 'anonymous')        drawImg.crossOrigin = 'Anonymous'        drawImg.src = currentImg        let addCanvas = document.createElement('canvas')        parentId.appendChild(addCanvas)        let canvas = parentId.lastElementChild        canvas.id = 'imgCanvas'        if (canvas.getContext) {          let ctx = canvas.getContext('2d')          drawImg.onload = function () {            canvas.width = 720            canvas.height = 500            ctx.drawImage(drawImg, 0, 0, 720, 500)          }        }      })    },    // 打码    dialogCode (img) {      let parentId = document.getElementById('parentId')      let canvas = document.getElementById('imgCanvas')      if (canvas.getContext) {        let ctx = canvas.getContext('2d')        let drawImage = new Image()        drawImage.crossOrigin = 'Anonymous'        drawImage.src = img        drawImage.onload = () => {          ctx.drawImage(drawImage, 0, 0, 720, 500)        }        parentId.onmousedown = e => {          ctx.clearRect(0, 0, canvas.width, canvas.height)          ctx.drawImage(drawImage, 0, 0, 720, 500)          this.flag = true          this.clickX = e.offsetX // 鼠标点击时的X          this.clickY = e.offsetY // 鼠标点击时的Y        }        parentId.onmouseup = () => {          this.flag = false        }        parentId.onmousemove = e => {          if (this.flag) {            ctx.clearRect(0, 0, canvas.width, canvas.height)            ctx.drawImage(drawImage, 0, 0, 720, 500)            ctx.beginPath()            let pixels = [] // 二维数组，每个子数组有5个值（绘制矩形左上角的X坐标、y坐标，矩形的宽、高，生成的4位随机数用于颜色值）            for (let x = 0; x < (e.offsetX - this.clickX) / 15; x++) {              for (let y = 0; y < (e.offsetY - this.clickY) / 15; y++) {                pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])              }              for (let y = 0; y > (e.offsetY - this.clickY) / 15; y--) {                pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])              }            }            for (let x = 0; x > (e.offsetX - this.clickX) / 15; x--) {              for (let y = 0; y > (e.offsetY - this.clickY) / 15; y--) {                pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])              }              for (let y = 0; y < (e.offsetY - this.clickY) / 15; y++) {                pixels.push([(x * 15 + this.clickX), (y * 15 + this.clickY), 15, 15, Math.floor(Math.random() * 9999)])              }            }            for (let i = 0; i < pixels.length; i++) {              ctx.fillStyle = '#bf' + pixels[i][4]              ctx.fillRect(pixels[i][0], pixels[i][1], pixels[i][2], pixels[i][3])            }            ctx.fill()            ctx.closePath()          }        }      }    },    // 保存    dialogUpload () {      let canvas = document.getElementById('imgCanvas')      let tempImg = canvas.toDataURL('image/png')      let imgURL = document.getElementById('imgURL')      imgURL.crossOrigin = 'Anonymous'      imgURL.src = tempImg    }  }})</script></html>

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