Vue、fabricJS 画布实现自由绘制折线

作者GitHub：https://github.com/gitboyzcf 有兴趣可关注

Vue3代码，Vue2相似改吧改吧

前言

Fabric.js

Fabric.js（英文官网）是一个强大而简单的 Javascript HTML5画布库（也就是针对canvas进行的封装操作，使用起来更方便）

Fabric在画布元素的顶部提供交互式对象模型、Fabric还具有SVG到画布（以及画布到SVG）解析器

安装

npm install fabric --save
or
pnpm install fabric --save
or
yarn add fabric --save

实现

Demo.vue

<script setup>
import { fabric } from 'fabric'
let canvas = null // 画布实例
let currentPolyline = null // 临时折线
let points = []

// 初始化画布
const init = () => {
  canvas = new fabric.Canvas('c')
  canvas.selectionColor = 'transparent'
  canvas.selectionBorderColor = 'transparent'
  canvas.skipTargetFind = true // 禁止选中
  canvas.on('mouse:down', canvasMouseDown) // 鼠标在画布上按下
  canvas.on('mouse:move', canvasMouseMove) // 鼠标在画布上移动
  canvas.on('mouse:dblclick', canvasMouseDblclick) // 鼠标在画布上双击
}

// 创建折线
const createPolyline = (e) => {
  const currentPoint = e.absolutePointer
  currentPolyline = new fabric.Polyline(
    [
      { x: currentPoint.x, y: currentPoint.y },
      { x: currentPoint.x, y: currentPoint.y }
    ],
    {
      fill: 'transparent',
      stroke: 'red',
      objectCaching: false
    }
  )
  canvas.add(currentPolyline)
}

// 修改当前正在创建的折线
const changeCurrentPolyline = (e) => {
  const currentPoint = e.absolutePointer

  let points = currentPolyline.points

  points.push({
    x: currentPoint.x,
    y: currentPoint.y
  })
  canvas.requestRenderAll()
}

// 折线橡皮带
const changePolylineBelt = (e) => {
  const currentPoint = e.absolutePointer
  let points = currentPolyline.points

  points[points.length - 1].x = currentPoint.x
  points[points.length - 1].y = currentPoint.y

  canvas.requestRenderAll()
}

// 完成折线绘制
const finishPolyline = (e) => {
  const currentPoint = e.absolutePointer
  let points = currentPolyline.points
  points[points.length - 1].x = currentPoint.x
  points[points.length - 1].y = currentPoint.y

  points.pop()
  points.pop()
  // 按需添加自闭合代码
  // if (points[0].x != points[points.length - 1].x && points[0].y != points[points.length - 1].y) {
   	// changeCurrentPolyline({ absolutePointer: { x: points[0].x, y: points[0].y } })
  // }
  canvas.remove(currentPolyline)

  if (points.length > 1) {
    let polyline = new fabric.Polyline(points, {
      stroke: 'red',
      fill: 'transparent'
    })

    canvas.add(polyline)
  }
  currentPolyline = null

  canvas.requestRenderAll()
}

// 鼠标在画布上按下
const canvasMouseDown = (e) => {
  if (currentPolyline === null) {
    createPolyline(e)
  } else {
    changeCurrentPolyline(e)
  }
}

// 鼠标在画布上移动
const canvasMouseMove = (e) => {
  if (currentPolyline) {
    changePolylineBelt(e)
  }
}

// 鼠标在画布上双击
const canvasMouseDblclick = (e) => {
  finishPolyline(e)
}

onMounted(() => {
  init()
})
</script>

<template>
  <div>
    <canvas id="c" width="500" height="470" style="border: 1px solid #ccc"></canvas>
  </div>
</template>

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