canvas学习时钟案例

Canvas绘制的时钟效果

html

<html>
    <head>
        <meta name="viewport" content="width=device-width,initial-scale=1">
        <title>canvas clock</title>
        <style type="text/css">
        div{
            text-align: center;
            margin-top: 250px;
        }
        #clock{
            border: 1px solid #ccc;
        }
        </style>
    </head>
    <body>
        <div>
            <canvas id="clock" height="200px" width="200px"></canvas>
        </div>
        <script type="text/javascript" src="clock.js"></script>
    </body>
</html>

var dom=document.getElementById("clock");
var ctx=dom.getContext('2d');
var width=ctx.canvas.width;
var height=ctx.canvas.height;
var r=width/2;
var rem=width/200;

function drawBackground(){
    ctx.save();
    ctx.translate(r,r);
    ctx.beginPath();
    ctx.lineWidth=10*rem;
    ctx.arc(0,0,r-ctx.lineWidth/2,0,2*Math.PI,false);
    ctx.stroke();

    var hourNumbers=[3,4,5,6,7,8,9,10,11,12,1,2];
    ctx.font=18*rem+'px Arial';
    ctx.textAlign='center';
    ctx.textBaseline='middle';
    hourNumbers.forEach(function(number,i){
        var rad=2*Math.PI/12*i;
        var x=Math.cos(rad)*(r-30*rem);
        var y=Math.sin(rad)*(r-30*rem);
        ctx.fillText(number,x,y);
    });
    for(var i=0;i<60;i++){
        var rad =2*Math.PI/60*i;
        var x=Math.cos(rad)*(r-18*rem);
        var y=Math.sin(rad)*(r-18*rem);
        ctx.beginPath();
        if(i%5===0){
            ctx.fillStyle='#000';
            ctx.arc(x,y,2*rem,0,2*Math.PI,false);
        }else{
            ctx.fillStyle='#ccc';
            ctx.arc(x,y,2*rem,0,2*Math.PI,false);
        }
        ctx.fill();
    }
}
function drawHour(hour,minute){
    ctx.save();
    ctx.beginPath();
    var rad=2*Math.PI/12*hour;
    var mrad=2*Math.PI/12/60*minute;
    ctx.rotate(rad+mrad);
    ctx.lineWidth=6*rem;
    ctx.lineCap='round';
    ctx.moveTo(0,10*rem);
    ctx.lineTo(0,-r/2);
    ctx.stroke();
    ctx.restore();
}
function drawMinute(minute){
    ctx.save();
    ctx.beginPath();
    var rad=2*Math.PI/60*minute;
    ctx.rotate(rad);
    ctx.lineWidth=3*rem;
    ctx.lineCap='round';
    ctx.moveTo(0,10*rem);
    ctx.lineTo(0,-r+30*rem);
    ctx.stroke();
    ctx.restore();
}
function drawSecond(second){
    ctx.save();
    ctx.beginPath();
    ctx.fillStyle="#c14543";
    var rad=2*Math.PI/60*second;
    ctx.rotate(rad);
    ctx.moveTo(-2*rem,20*rem);
    ctx.lineTo(2*rem,20*rem);
    ctx.lineTo(1,-r+18*rem);
    ctx.lineTo(-1,-r+18*rem);
   ctx.fill();
    ctx.restore();
}
function drawDot(){
    ctx.beginPath();
    ctx.fillStyle="#fff";
    ctx.arc(0,0,3*rem,0,2*Math.PI,false);
    ctx.fill();
}

function draw(){
    ctx.clearRect(0,0,width,height);
    var now =new Date();
    var hour=now.getHours();
    var minute=now.getMinutes();
    var second=now.getSeconds();
    drawBackground();
    drawHour(hour,minute);
    drawMinute(minute);
    drawSecond(second);
    drawDot();
    ctx.restore();
}
draw();
setInterval(draw,1000);

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