参考书目：《HTML5 Canvas核心技术 图形、动画与游戏开发》
用HTML5 Canvas实现一个基本的时钟程序
1-4.html
<!DOCTYPE html>
<html>
<head>
<title>Clock</title>
<style>
body {
background: #dddddd;
}
#canvas {
position: absolute;
left: 0px;
top: 0px;
margin: 20px;
background: #ffffff;
border: thin solid #aaaaaa;
}
</style>
</head>
<body>
<canvas id='canvas' width='400' height='400'>
Canvas not supported
</canvas>
<script src='1-4.js'></script>
</body>
</html>
1-4.js
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
FONT_HEIGHT = 15,
MARGIN = 35,
HAND_TRUNCATION = canvas.width/25,
HOUR_HAND_TRUNCATION = canvas.width/10,
NUMERAL_SPACING = 20,
RADIUS = canvas.width/2 - MARGIN,
HAND_RADIUS = RADIUS + NUMERAL_SPACING;
function drawCircle() {
context.beginPath();
context.arc(canvas.width/2, canvas.height/2,
RADIUS, 0, Math.PI*2, true);
context.stroke();
}
function drawNumerals() {
var numerals = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ],
angle = 0,
numeralWidth = 0;
numerals.forEach(function(numeral) {
angle = Math.PI/6 * (numeral-3);
numeralWidth = context.measureText(numeral).width;
context.fillText(numeral,
canvas.width/2 + Math.cos(angle)*(HAND_RADIUS) - numeralWidth/2,
canvas.height/2 + Math.sin(angle)*(HAND_RADIUS) + FONT_HEIGHT/3);
});
}
function drawCenter() {
context.beginPath();
context.arc(canvas.width/2, canvas.height/2, 5, 0, Math.PI*2, true);
context.fill();
}
function drawHand(loc, isHour) {
var angle = (Math.PI*2) * (loc/60) - Math.PI/2,
handRadius = isHour ? RADIUS - HAND_TRUNCATION-HOUR_HAND_TRUNCATION
: RADIUS - HAND_TRUNCATION;
context.moveTo(canvas.width/2, canvas.height/2);
context.lineTo(canvas.width/2 + Math.cos(angle)*handRadius,
canvas.height/2 + Math.sin(angle)*handRadius);
context.stroke();
}
function drawHands() {
var date = new Date,
hour = date.getHours();
hour = hour > 12 ? hour - 12 : hour;
drawHand(hour*5 + (date.getMinutes()/60)*5, true, 0.5);
drawHand(date.getMinutes(), false, 0.5);
drawHand(date.getSeconds(), false, 0.2);
}
function drawClock() {
context.clearRect(0,0,canvas.width,canvas.height);
drawCircle();
drawCenter();
drawHands();
drawNumerals();
}
context.font = FONT_HEIGHT + 'px Arial';
loop = setInterval(drawClock, 1000);
效果如图：
