针对上一篇canvas画板的优化和封装

针对上一篇的canvas画板的优化和封装

为了方便以后的使用我将canvas画板封装成了一个对象，使用的时候只需引入之后new成对象即可使用。并有清空画板、改变画笔颜色、粗细、历史上一笔、下一笔等功能
html

   .btnBox {   margin: 0 auto 20px auto;   width: 300px;   padding: 10px;   box-sizing: border-box;   .item{     width: 100%;     display: flex;     justify-content: center;     align-items: center;     .el-button{       width: 100%     }     .size{       margin: 0 10px;       border-radius: 50%;     }     .el-slider{       flex: 1;       .el-slider__runway.show-input{         margin-right: 110px;       }       .el-slider__input{         width: 95px       }     }   } } 

 封装的对象

import store from '../vuex_study_module/store'  export default class Draw {   constructor(tag, historyList, background, color, size) {     this.canvas           = document.getElementById(tag)     this.ctx              = this.canvas.getContext("2d")     this.width            = this.canvas.offsetWidth     this.height           = this.canvas.offsetHeight     this.canvas.width     = this.width     this.canvas.height    = this.height     this.canvasOffsetTop  = this.canvas.offsetTop//移动端canvas距离顶部的距离     this.canvasOffsetLeft = this.canvas.offsetLeft//移动端canvas距离左边的距离     this.startPosition    = []//当前的点     this.isdraw           = false//是否在作画     this.history          = historyList ? historyList : []//所有的历史画笔集合     this.isInit           = false//是否为初始化     this.currentPen       = []//当前画笔     this.drawStep         = 0//当前第几笔画     this.penSize          = size//画笔大小     this.penColor         = color//画笔颜色     this.backGround       = background ? background : '#999999'//画布背景色     this.ctx.fillStyle    = this.backGround     this.ctx.lineWidth    = size * 2 + 1//线的宽度     this.ctx.strokeStyle  = color//点的颜色     this.ctx.fillRect(0, 0, this.width, this.height)//画布大小     this.canvas.addEventListener('touchmove', function (e) { //禁止页面滚动       e.preventDefault();     }, {passive: false}); //passive 参数不能省略，用来兼容ios和android     this.canvas.removeEventListener('touchend', function (e) { //解除页面滚动       e.preventDefault();     }, {passive: false});     this.canvas.onmousedown = res => {       //指针在canvas上点击       this.isdraw = true;       this.startPosition[0] = res.offsetX;       this.startPosition[1] = res.offsetY;       this.drawLine(this.startPosition[0], this.startPosition[1]);     }     this.canvas.onmouseup = res => {       //指针在canvas上放开       if (!this.isdraw) return;       this.clear();     }     this.canvas.onmouseout = res => {       //指针移出canvas       if (!this.isdraw) return;       this.clear();     }     this.canvas.onmousemove = res => {       //指针在canvas移动       if (!this.isdraw) return;       this.drawLine(res.offsetX, res.offsetY);     }     this.canvas.ontouchstart = res => {       // 手指触摸开始       this.isdraw = true;       this.startPosition[0] = res.changedTouches[0].pageX - this.canvasOffsetLeft;       this.startPosition[1] = res.changedTouches[0].pageY - this.canvasOffsetTop;       this.drawLine(this.startPosition[0], this.startPosition[1]);     }     this.canvas.ontouchmove = res => {       //手指触摸移动       if (!this.isdraw) return;       this.drawLine(res.changedTouches[0].pageX - this.canvasOffsetLeft, res.changedTouches[0].pageY - this.canvasOffsetTop);     }     this.canvas.ontouchend = res => {       // 手指触摸结束       if (!this.isdraw) return;       this.clear();     }   }   drawLine(X, Y) {     //画图     if (!this.isdraw) return;     this.ctx.beginPath();//画圆     this.ctx.arc(X, Y, this.penSize, 0, 2 * Math.PI)     this.ctx.closePath();     this.ctx.fillStyle = this.penColor;     this.ctx.fill();     this.ctx.beginPath()//画线     this.ctx.moveTo(this.startPosition[0], this.startPosition[1] + 0.5);     this.ctx.lineTo(X, Y + 0.5);     this.ctx.stroke();     this.ctx.save();     this.startPosition = [X, Y];     if (!this.isInit) this.currentPen.push(this.startPosition)   }   clear() {     // 停止画笔     this.isdraw = false;     this.startPosition = [];     this.history.push({size: this.penSize,color: this.penColor,list: this.currentPen});     this.currentPen = [];     this.drawStep = this.history.length - 1     store.commit('setPenList', this.history)   }   historyDrawPen(penList = []) {     // 画历史画笔     this.history = penList     this.isdraw = true     this.isInit = true     this.resetCanvas()     for(let i = 0;i < penList.length;i++) {       if (this.drawStep < i) break;       if (penList[i].list.length == 0) {         this.resetCanvas()       } else {         this.setColor(penList[i].color)         this.setPenSize(penList[i].size)         this.startPosition = [];//避免画笔的最后一点会和下一个画笔的前一点链接起来         for(let j = 0;j < penList[i].list.length;j++) {           this.drawLine(penList[i].list[j][0], penList[i].list[j][1])         }       }     }     this.isdraw = false     this.isInit = false     this.startPosition = []   }   getHistoryPoint() {     // 返回画笔记录     return this.history   }   setColor(color) {     // 设置画笔的颜色     this.ctx.strokeStyle = color     this.penColor = color   }   setPenSize(size) {     // 设置画笔的粗细     this.penSize = size     this.ctx.lineWidth = size * 2 + 1   }   resetCanvas() {     //清空canvas     this.currentPen = [];     this.ctx.fillStyle = this.backGround;     this.ctx.fillRect(0, 0, this.width, this.height)     if (this.isInit) return     this.history.push({size: this.penSize,color: this.penColor,list: []});     this.drawStep = this.history.length - 1     store.commit('setPenList',this.history)   }   init(penList) {     // 初始化画布     this.drawStep = penList ? penList.length - 1 : 0     this.historyDrawPen(penList)   }   after() {     // 下一笔     if (this.drawStep >= this.history.length - 1) return {code: 404, msg: '没有下一个笔画了'}     this.drawStep = this.drawStep + 1     this.historyDrawPen(this.history)     return {code: 200, msg: '恢复下一笔'}   }   front() {     // 上一笔     if (this.drawStep < 0) return {code: 404, msg: '没有前一个笔画了'}     this.drawStep = this.drawStep - 1     this.historyDrawPen(this.history)     return {code: 200, msg: '恢复前一笔'}   } }