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使用cavans绘制随机圆点

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一、定义标签

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<canvas></canvas>

二、业务代码

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// 获取canvas元素，并设置其绘图上下文以便进行2D绘图
const cvs = document.querySelector("canvas");
const ctx = cvs.getContext("2d");

function init() {
  // window.innerWidth 浏览器窗口的内部宽度（不包括工具栏或滚动条）
  // devicePixelRatio 设备比列
  cvs.width = window.innerWidth * devicePixelRatio;
  cvs.height = window.innerHeight * devicePixelRatio;
}
init();

/**
 * 获取[min, max] 范围内的随机整数
 * @return {Number}
 */
function getRandom(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

// 定义Point类
class Point {
  constructor() {
    this.r = 6;
    this.x = getRandom(0, cvs.width - this.r / 2);
    this.y = getRandom(0, cvs.height - this.r / 2);
    this.xSpeed = getRandom(-50, 50);
    this.ySpeed = getRandom(-50, 50);
    this.lastDrawTime = null;
  }
  // 定义绘制方法
  draw() {
    if (this.lastDrawTime) {
      // 根据运动时间，计算出当前位置
      const now = Date.now();
      const t = (now - this.lastDrawTime) / 1000;
      let x = this.x + this.xSpeed * t;
      let y = this.y + this.ySpeed * t;
      if (x <= this.r || x >= cvs.width - this.r) {
        this.xSpeed *= -1;
      }
      if (y <= this.r || y >= cvs.height - this.r) {
        this.ySpeed *= -1;
      }
      this.x = x;
      this.y = y;
    }
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.r, 0, Math.PI * 2);
    ctx.fillStyle = "rgb(200,200,200)";
    ctx.fill();
    this.lastDrawTime = Date.now();
  }
}

class Graph {
  constructor(pointNumber = 30, maxDis = 500) {
    this.points = new Array(pointNumber).fill(0).map(() => new Point());
    this.maxDis = maxDis;
  }
  draw() {
    requestAnimationFrame(() => {
      this.draw();
    });
    ctx.clearRect(0, 0, cvs.width, cvs.height);
    for (let i = 0; i < this.points.length; i++) {
      const p1 = this.points[i];
      p1.draw();
      for (let j = i + 1; j < this.points.length; j++) {
        const p2 = this.points[j];
        const d = Math.sqrt((p2.x - p1.x) ** 2, (p2.y - p1.y) ** 2);
        if (d > this.maxDis) {
          continue;
        }
        ctx.beginPath();
        ctx.moveTo(p1.x, p1.y);
        ctx.lineTo(p2.x, p2.y);
        ctx.closePath();
        ctx.strokeStyle = `rgba(200,200,200,${this.maxDis})`;
        ctx.stroke();
      }
    }
  }
}

const g = new Graph();
g.draw();

三、效果图

canvas

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