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  • bouncing-balls

    效果如下:

    代码目录如下:

    <!DOCTYPE html>
    <html lang="zh-CN">
      <head>
        <meta charset="utf-8">
        <title>弹球</title>
        <link rel="stylesheet" href="style.css">
        <script src="main.js" defer></script>
      </head>
    
      <body>
        <h1>弹球</h1>
        <canvas></canvas>
      </body>
    </html>
    
    //main.js
    const BALLS_COUNT = 25;
    const BALL_SIZE_MIN = 10;
    const BALL_SIZE_MAX = 20;
    const BALL_SPEED_MAX = 7;
    
    // 设定画布
    const canvas = document.querySelector('canvas');
    const ctx = canvas.getContext('2d');
    
    // 将画布窗尺寸置为窗口内尺寸
    const width = canvas.width = window.innerWidth;
    const height = canvas.height = window.innerHeight;
    
    // 定义一个数组来保存所有的球
    const balls = [];
    
    // 生成随机数的函数
    function random(min,max) {
      return Math.floor(Math.random()*(max-min)) + min;
    }
    
    // 生成随机颜色的函数
    function randomColor() {
        return 'rgb(' +
               random(0, 255) + ', ' +
               random(0, 255) + ', ' +
               random(0, 255) + ')';
    }
    
    // 定义 Ball 构造器
    function Ball(x, y, velX, velY, color, size) {
      this.x = x;
      this.y = y;
      this.velX = velX;
      this.velY = velY;
      this.color = color;
      this.size = size;
    }
    
    // 定义绘制球的函数
    Ball.prototype.draw = function() {
      ctx.save();
      ctx.beginPath();
      ctx.fillStyle = this.color;
      ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
      ctx.fill();
      ctx.restore();
    };
    
    // 定义更新球的函数
    Ball.prototype.update = function() {
      if((this.x + this.size) >= width) {
        this.velX = -(this.velX);
      }
    
      if((this.x - this.size) <= 0) {
        this.velX = -(this.velX);
      }
    
      if((this.y + this.size) >= height) {
        this.velY = -(this.velY);
      }
    
      if((this.y - this.size) <= 0) {
        this.velY = -(this.velY);
      }
    
      this.x += this.velX;
      this.y += this.velY;
    };
    
    // 定义碰撞检测函数
    Ball.prototype.collisionDetect = function() {
      for(let j = 0; j < balls.length; j++) {
        if( this !== balls[j]) {
          const dx = this.x - balls[j].x;
          const dy = this.y - balls[j].y;
          const distance = Math.sqrt(dx * dx + dy * dy);
    
          if (distance < this.size + balls[j].size) {
            balls[j].color = this.color = randomColor();        
          }
        }
      }
    };
    
    // 定义一个循环来不停地播放
    function loop() {
      ctx.fillStyle = 'rgb(0, 0, 0, 0.25)';
      ctx.fillRect(0, 0, width, height);
    
      while(balls.length < BALLS_COUNT) {
        const size = random(BALL_SIZE_MIN, BALL_SIZE_MAX);
        const ball = new Ball(
          // 为避免绘制错误,球至少离画布边缘球本身一倍宽度的距离
          random(0 + size, width - size),
          random(0 + size, height - size),
          random(-BALL_SPEED_MAX, BALL_SPEED_MAX),
          random(-BALL_SPEED_MAX, BALL_SPEED_MAX),
          randomColor(),
          size
        );
        balls.push(ball);
      }
    
      for(let i = 0; i < balls.length; i++) {
        balls[i].draw();
        balls[i].update();
        balls[i].collisionDetect();
      }
    
      requestAnimationFrame(loop);
    }
    
    loop();
    
    //style.css
    body {
      margin: 0;
      overflow: hidden;
      font-family: '微软雅黑', sans-serif;
      height: 100%;
    }
      
    h1 {
      font-size: 2rem;
      letter-spacing: -1px;
      position: absolute;
      margin: 0;
      top: -4px;
      right: 5px;
      color: transparent;
      text-shadow: 0 0 4px white;
    }
    
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  • 原文地址:https://www.cnblogs.com/smart-girl/p/10717766.html
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