3. [代码][JavaScript]代码     // 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 = 'http://static.oschina.net/uploads/space/2012/0712/125855_nnla_89964.png'; setInterval(drawScene, 1000); // loop drawScene });