之前学习了下html5中的canvas元素，为了练练手就实现了一个简易的时钟。时钟本身并不复杂，也没有使用图片进行美化，不过麻雀虽小五脏俱全，下面就与大家分享一下：
演示效果：
html代码：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Clock</title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
.canvas{
margin-left: 20px;
margin-top: 20px;
border: solid 1px;
}
</style>
</head>
<body onload= "main()">
<canvas class = "canvas" id="canvasId" width = '500px' height = '400px'></canvas>
<script type= "text/javascript" src = "Clock.js"></script>
</body>
</html>
JS代码:
var Canvas = {};
Canvas.cxt = document.getElementById('canvasId').getContext('2d');
Canvas.Point = function(x, y){
this.x = x;
this.y = y;
};
/*擦除canvas上的所有图形*/
Canvas.clearCxt = function(){
var me = this;
var canvas = me.cxt.canvas;
me.cxt.clearRect(0,0, canvas.offsetWidth, canvas.offsetHeight);
};
/*时钟*/
Canvas.Clock = function(){
var me = Canvas,
c = me.cxt,
radius = 150, /*半径*/
scale = 20, /*刻度长度*/
minangle = (1/30)*Math.PI, /*一分钟的弧度*/
hourangle = (1/6)*Math.PI, /*一小时的弧度*/
hourHandLength = radius/2, /*时针长度*/
minHandLength = radius/3*2, /*分针长度*/
secHandLength = radius/10*9, /*秒针长度*/
center = new me.Point(c.canvas.width/2, c.canvas.height/2); /*圆心*/
/*绘制圆心（表盘中心）*/
function drawCenter(){
c.save();
c.translate(center.x, center.y);
c.fillStyle = 'black';
c.beginPath();
c.arc(0, 0, radius/20, 0, 2*Math.PI);
c.closePath();
c.fill();
c.stroke();
c.restore();
};
/*通过坐标变换绘制表盘*/
function drawBackGround(){
c.save();
c.translate(center.x, center.y); /*平移变换*/
/*绘制刻度*/
function drawScale(){
c.moveTo(radius - scale, 0);
c.lineTo(radius, 0);
};
c.beginPath();
c.arc(0, 0, radius, 0, 2*Math.PI, true);
c.closePath();
for (var i = 1; i <= 12; i++) {
drawScale();
c.rotate(hourangle); /*旋转变换*/
};
/*绘制时间(3,6,9,12)*/
c.font = " bold 30px impack"
c.fillText("3", 110, 10);
c.fillText("6", -7, 120);
c.fillText("9", -120, 10);
c.fillText("12", -16, -100);
c.stroke();
c.restore();
};
/*绘制时针(h: 当前时（24小时制）)*/
this.drawHourHand = function(h){
h = h === 0? 24: h;
c.save();
c.translate(center.x, center.y);
c.rotate(3/2*Math.PI);
c.rotate(h*hourangle);
c.beginPath();
c.moveTo(0, 0);
c.lineTo(hourHandLength, 0);
c.stroke();
c.restore();
};
/*绘制分针（m: 当前分）*/
this.drawMinHand = function(m){
m = m === 0? 60: m;
c.save();
c.translate(center.x, center.y);
c.rotate(3/2*Math.PI);
c.rotate(m*minangle);
c.beginPath();
c.moveTo(0, 0);
c.lineTo(minHandLength, 0);
c.stroke();
c.restore();
};
/*绘制秒针（s：当前秒）*/
this.drawSecHand = function(s){
s = s === 0? 60: s;
c.save();
c.translate(center.x, center.y);
c.rotate(3/2*Math.PI);
c.rotate(s*minangle);
c.beginPath();
c.moveTo(0, 0);
c.lineTo(secHandLength, 0);
c.stroke();
c.restore();
};
/*依据本机时间绘制时钟*/
this.drawClock = function(){
var me = this;
function draw(){
var date = new Date();
Canvas.clearCxt();
drawBackGround();
drawCenter();
me.drawHourHand(date.getHours() + date.getMinutes()/60);
me.drawMinHand(date.getMinutes() + date.getSeconds()/60);
me.drawSecHand(date.getSeconds());
}
draw();
setInterval(draw, 1000);
};
};
var main = function(){
var clock = new Canvas.Clock();
clock.drawClock();
};
代码中涉及到了一些简单的canvas元素API 大家度娘一下即可
以上就是本文的全部内容了，希望对大家学习canvas能够有所帮助。
