使用canvas一步步实现图片打码功能
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>