[JavaScript] Canvas 动画实例

<!DOCTYPE html>
<html lang="en">

<head>
<meta name="description" content="canvas zoom example">
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <meta http-equiv="X-UA-Compatible" content="ie=edge" />
  <title>zoom</title>
</head>

<body>
  <canvas id="canvas"></canvas>
</body>

</html>

const canvas = document.querySelector("#canvas");
const ctx = canvas.getContext("2d");

canvas.width = canvas.style.width || 500;
canvas.height = canvas.style.height || 500;

const w = canvas.width;
const h = canvas.height;

class Color {
  constructor(r = 255, g = 255, b = 255, a = 1) {
    this.r = r;
    this.g = g;
    this.b = b;
    this.a = a;
  }

  getColor() {
    return `rgba(${this.r}, ${this.g}, ${this.b}, ${this.a})`;
  }

  static getRandomInt(num) {
    return Math.ceil(Math.random() * num);
  }

  static getRandomColor() {
    const r = this.getRandomInt(255);
    const g = this.getRandomInt(255);
    const b = this.getRandomInt(255);
    const a = Math.random().toFixed(2);
    return new Color(r, g, b, a);
  }
}

// 目前仅支持方形
class Node {
  constructor({
    x, y, w, h, color
  }) {
    this.x = x || 0;
    this.y = y || 0;
    this.w = w || 10;
    this.h = h || 10;
    this.color = color || Color.getRandomColor();
  }
  render() {
    const _currentTranslate = ctx._currentTranslate;
    ctx.fillStyle = this.color.getColor();
    ctx.fillRect(this.x - _currentTranslate[0], this.y - _currentTranslate[1], this.w, this.h);
  }
}

const objects = [...Array(Math.ceil(Math.random() * 100))].map(() => {
  return new Node({
    x: Math.ceil((Math.random() - 0.5) * 1000),
    y: Math.ceil((Math.random() - 0.5) * 1000),
    w: Math.ceil(Math.random() * 100 + 5),
    h: Math.ceil(Math.random() * 100 + 5)
  });
});

let zoom = 1;
let sign2 = -1;
const render = () => {
  if (zoom <= 0.01 || zoom >= 2) {
    sign2 *= -1;
  }
  zoom += sign2 * 0.01;

  ctx.clearRect(0, 0, w, h);

  ctx.save();

  // ctx.translate(0, 0);
  ctx.translate(w / 2, h / 2);
  ctx._currentTranslate = [w / 2, h / 2];

  ctx.scale(zoom, zoom);

  objects.forEach(node => {
    node.render();
  });

  ctx.font = "24px serif";
  ctx.textAlign = "center";
  ctx.fillStyle = new Color(255, 255, 0).getColor();
  const _currentTranslate = ctx._currentTranslate;
  ctx.fillText("Hello world!", 0 - _currentTranslate[0], 0 - _currentTranslate[1]);

  ctx.restore();

  ctx.save();
  ctx.fillStyle = '#fff';
  ctx.fillRect(0, 0, 80, 20);
  ctx.font = "18px serif";
  ctx.textBaseline = 'top';
  ctx.textAlign = "left";
  ctx.fillStyle = '#000';
  ctx.fillText("zoom: " + zoom.toFixed(2), 0, 0);
  ctx.restore();
};

function animate() {
  render();
  requestAnimationFrame(animate);
}

animate();

#canvas {
  margin: 0 auto;
  height: 500px;
  width: 500px;
}

posted on 2020-06-02 20:14 晏过留痕阅读(407) 评论(0) 编辑收藏举报