angular13 canvas画板绘图

angular13 canvas 绘图组件代码实现，供个人学习

    <canvas id="canvas" [width]="cwidth" [height]="cheight"> canvas>

    <span class="eraser" (click)="getEraser()">清空/橡皮擦span>
    <input type="button" value="生成图片" (click)="change()"><br>
    <img id="image" [src]="src"  width="500px" height="200px">
    
    <img id="scream"  src="assets/R-A.jpg"> 

#canvas{
  cursor:crosshair;
  // background-color: white;
  border:5px solid rgb(194, 194, 194);
}

import { Component, OnInit } from '@angular/core';

@Component({
  selector: 'app-blackboard',
  templateUrl: './blackboard.component.html',
  styleUrls: ['./blackboard.component.scss']
})

export class BlackboardComponent implements OnInit {


  ngOnInit() {
    this.drawCanvas();
  }
 
  cwidth = 800
  cheight = 600
  canvas: any;
  ctx:any;
  //按下标记
   onoff=false; //默认是未按下
  //设置颜色默认为白色
   linecolor = "red";
  //宽度默认为4
   linw = 4;
   src = ""
   lastLoc = { x: 0, y: 0};//初始位置值



  //生成图片
  change():void{
  this.src = this.canvas.toDataURL("image/jpg");
  console.log( "接受到的图片："+ this.src)
  }

  //绘制画板中内容
  drawCanvas() {
    this.canvas = document.getElementById('canvas');
    this.ctx = this.canvas.getContext("2d");
    var imgUrl = document.getElementById("scream");

    //画一个黑色矩形
    this.ctx.fillStyle="#ffffff";
    this.ctx.fillRect(0,0,600,400);

    // 等待加载完成再绘制
      setTimeout(() => {   //延时两秒执行读取方法
        this.ctx.drawImage(imgUrl,0,0, this.cwidth, this.cheight);
      }, 500)
  
 
    this.canvas.onmousedown = (e: { pageX: any; pageY: any; clientX: number; clientY: number; } ) => {
      	this.onoff=true;
        this.lastLoc = this.windowCanvas(e.clientX, e.clientY);
    }


 //鼠标移动事件，事件绑定
 this.canvas.onmousemove = (e: any) => {
  if (this.onoff) {
      var curLoc = this.windowCanvas(e.clientX, e.clientY);
      this.ctx.beginPath();
      this.ctx.moveTo(this.lastLoc.x, this.lastLoc.y);
      this.ctx.lineTo(curLoc.x, curLoc.y);
      this.ctx.strokeStyle=this.linecolor;
      this.ctx.lineWidth=this.linw;
      this.ctx.lineCap="round";
      this.ctx.stroke();
      this.lastLoc = curLoc;
  }
  console.log("...移动onmousemove");
  }

  //鼠标按下，松开，移动，离开事件执行
    this.canvas.onmouseup = (e: { preventDefault: () => void; pageX: any; pageY: any; }) => {
      this.onoff = false;
    }
    this.canvas.onmouseout = (e: { preventDefault: () => void; }) => {
      this.onoff = false;
    }

  }


  /**
   * 获取canvas坐标
   */
   windowCanvas(x: number, y: number) {
    var ctxbox = this.canvas.getBoundingClientRect();
    console.log('canvas坐标', Math.round(x - ctxbox.left), Math.round(y - ctxbox.top));
    return { x: Math.round(x - ctxbox.left), y: Math.round(y - ctxbox.top) };
  }


  /**
   * 橡皮擦：canvas的高度及宽度重置
   */
   getEraser() {
    this.canvas.width = this.cwidth;
    this.canvas.height = this.cheight;
  }
}