使用 HTML5 Canvas 制作时钟

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<!DOCTYPE html>
<html lang="en" >
    <head>
        <meta charset="utf-8" />
        <title>HTML5 时钟</title>
        <script src="https://cdn.staticfile.net/jquery/3.2.1/jquery.min.js"></script>
      <style>
        .clocks {
          height: 500px;
          margin: 25px auto;
          position: relative;
          width: 500px;
        }
      </style>
    </head>
    <body>
        <header>
            <h2>HTML5 时钟</h2>
        </header>
        <div class="clocks">
            <canvas id="canvas" width="500" height="500"></canvas>
        </div>
    </body>
</html>

HTML

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// inner variables
var canvas, ctx;
var clockRadius = 250;
var clockImage;
​
// draw functions :
function clear() { // clear canvas function
    ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}
​
function drawScene() { // main drawScene function
    clear(); // clear canvas
​
    // get current time
    var date = new Date();
    var hours = date.getHours();
    var minutes = date.getMinutes();
    var seconds = date.getSeconds();
    hours = hours > 12 ? hours - 12 : hours;
    var hour = hours + minutes / 60;
    var minute = minutes + seconds / 60;
​
    // save current context
    ctx.save();
​
    // draw clock image (as background)
    ctx.drawImage(clockImage, 0, 0, 500, 500);
​
    ctx.translate(canvas.width / 2, canvas.height / 2);
    ctx.beginPath();
​
    // draw numbers
    ctx.font = '36px Arial';
    ctx.fillStyle = '#000';
    ctx.textAlign = 'center';
    ctx.textBaseline = 'middle';
    for (var n = 1; n <= 12; n++) {
        var theta = (n - 3) * (Math.PI * 2) / 12;
        var x = clockRadius * 0.7 * Math.cos(theta);
        var y = clockRadius * 0.7 * Math.sin(theta);
        ctx.fillText(n, x, y);
    }
​
    // draw hour
    ctx.save();
    var theta = (hour - 3) * 2 * Math.PI / 12;
    ctx.rotate(theta);
    ctx.beginPath();
    ctx.moveTo(-15, -5);
    ctx.lineTo(-15, 5);
    ctx.lineTo(clockRadius * 0.5, 1);
    ctx.lineTo(clockRadius * 0.5, -1);
    ctx.fill();
    ctx.restore();
​
    // draw minute
    ctx.save();
    var theta = (minute - 15) * 2 * Math.PI / 60;
    ctx.rotate(theta);
    ctx.beginPath();
    ctx.moveTo(-15, -4);
    ctx.lineTo(-15, 4);
    ctx.lineTo(clockRadius * 0.8, 1);
    ctx.lineTo(clockRadius * 0.8, -1);
    ctx.fill();
    ctx.restore();
​
    // draw second
    ctx.save();
    var theta = (seconds - 15) * 2 * Math.PI / 60;
    ctx.rotate(theta);
    ctx.beginPath();
    ctx.moveTo(-15, -3);
    ctx.lineTo(-15, 3);
    ctx.lineTo(clockRadius * 0.9, 1);
    ctx.lineTo(clockRadius * 0.9, -1);
    ctx.fillStyle = '#0f0';
    ctx.fill();
    ctx.restore();
​
    ctx.restore();
}
​
// initialization
$(function(){
    canvas = document.getElementById('canvas');
    ctx = canvas.getContext('2d');
​
    // var width = canvas.width;
    // var height = canvas.height;
​
clockImage = new Image();
clockImage.src = 'https://statiwww.jyshare.com/images/mix/125855_nnla_89964.png';
​
    setInterval(drawScene, 1000); // loop drawScene
});

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