79 lines
2.3 KiB
Markdown
79 lines
2.3 KiB
Markdown
---
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title: "H5 Canvas前端绘图库 Fabric 简单应用"
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categories: [ "前端技术" ]
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tags: [ ]
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draft: false
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slug: "fabricjs"
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date: "2020-12-09 12:46:00"
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---
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圣诞节又快到了，又到了全民给微信头像加圣诞帽的时候了。
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撸了一个纯前端实现的加圣诞帽的页面，[点击前往][1]
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## JS引用
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```js
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<script src="https://cdn.bootcdn.net/ajax/libs/fabric.js/4.2.0/fabric.min.js"></script>
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```
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直接用 bootcdn 引用 fabric.js 最新版
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## 构建 fabric 对象
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```html
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<div class="body" id="uploadContainer">
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<img id="export" alt="圣诞快乐" src="" />
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<canvas id="cvs"></canvas>
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<div style="display: none">
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<img id="img" src="" alt="" />
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<img class="hide" id="hat0" src="./hat0.png" />
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<!-- 此处省略其余帽子图像-->
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</div>
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```
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部分DOM内容，只保留关键组件
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```js
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var screenWidth = window.screen.width < 500 ? window.screen.width : 300 // 计算是最终输出大小（适配移动端）
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canvasFabric = new fabric.Canvas('cvs', {
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width: screenWidth ,
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height: screenWidth ,
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backgroundImage: new fabric.Image(img, {
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scaleX: screenWidth / img.width, // 强制缩放至正方形
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scaleY: screenWidth / img.height,
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})
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```
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要对 canvas进行操作，首先要构建一个对象
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```js
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hatInstance = new fabric.Image(hatImage, { // 以一个img DOM创建fabric图像对象
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top: 40,
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left: 50,
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scaleX: 100 / hatImage.width,
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scaleY: 100 / hatImage.height,
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cornerColor: '#0b3a42',
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cornerStrokeColor: '#fff',
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cornerStyle: 'circle',
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transparentCorners: false,
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rotatingPointOffset: 30,
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})
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hatInstance.setControlVisible('bl', false) // 默认的对象都会有控制大小的手柄，此处关闭几个
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hatInstance.setControlVisible('tr', false)
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hatInstance.setControlVisible('tl', false)
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hatInstance.setControlVisible('mr', false)
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hatInstance.setControlVisible('mt', false)
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canvasFabric.add(hatInstance) // 添加实例到画布中
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```
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随后就是在头像图上绘制圣诞帽
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创建一个 Image 对象，并将其添加到画布中。
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```js
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exportImage.src = canvasFabric.toDataURL({ width: screenWidth, height: screenWidth })
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```
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最终将画布内容输出到img DOM中，移动端长按保存，桌面端右键保存。
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## 源码
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[button color="light" icon="" url="https://cdn.rhyland.cn/typecho/2020/12/09/christmas_hat.zip" type="round"]点击下载[/button]
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[1]: https://blog.xingez.me/christmas_hat |