技术点:

• 状态保存 context.save()
• 状态恢复 context.restore()
• 旋转 context.rotate(弧度)
• 平移 context.translate(x,y) x,y 是需要移动到的目标位置坐标
• 缩放 context.scale(1.5,1.5) 1.5,1.5 是缩放比例, 将原来的画布放大1.5倍
• 画圆弧 context.arc(x,y,r,初始弧度, 最终弧度)
• 清空矩形内容context.clearRect(x,y,width,height)
• 时间(时,分,秒)的角度换算

点击此处查看Demo

效果图如下

CanvasClock

上代码

<canvas id="clock" width="400" height="400"></canvas>

canvas {
        border: 1px solid #000;
        display: block;
        margin: 100px auto;
    }

function Clock(options) {
    this._init(options);
}
Clock.prototype = {
    constructor: Clock,
    _init: function(options) {
        options = options || {};
        this.width = options.width || 400;
        this.height = options.height || 400;
        this.r = options.r || 180;
        this.clockR = options.r - 20 || 160;
        this.ctx = options.ctx || document.getElementById('clock').getContext('2d');
    },
    // 渲染表盘
    renderClock: function() {

        // 保存状态
        this.ctx.save();

        // 绘制外面的圈
        this.ctx.arc(0, 0, this.r, 0, 2 * Math.PI);
        this.ctx.strokeStyle = '#408000';
        this.ctx.lineWidth = 10;
        this.ctx.stroke();

        // 恢复状态
        this.ctx.restore();
    },
    renderPoint: function() {
        this.ctx.save();
        this.ctx.beginPath();
        this.ctx.fillStyle = '#FF6666';
        this.ctx.arc(0, 0, 8, 0, 2 * Math.PI);
        this.ctx.fill();
        this.ctx.restore();
    },
    // 渲染刻度
    renderScale: function() {
        // 保存状态
        this.ctx.save();
        // 绘制刻度
        this.ctx.beginPath();
        for (var i = 0; i < 60; i++) {
            var x = Math.cos(i * 6 * Math.PI / 180) * this.clockR;
            var y = Math.sin(i * 6 * Math.PI / 180) * this.clockR;
            this.ctx.beginPath();
            var r = 3;
            var text = 1;
            if (i % 5 == 0) {
                r = 5;
                this.ctx.save();
                var v = parseInt(i / 5);
                text = v == 0 ? 12 : v;
                this.ctx.textAlign = 'center';
                this.ctx.textBaseline = 'middle';
                this.ctx.font = '18px Monaco';
                this.ctx.fillStyle = '#000';
                var xx = Math.cos(i * 6 * Math.PI / 180) * (this.clockR + 15);
                var yy = Math.sin(i * 6 * Math.PI / 180) * (this.clockR + 15);
                this.ctx.translate(xx, yy);
                this.ctx.rotate(90 * Math.PI / 180);
                this.ctx.fillText(text, 0, 0);
                this.ctx.restore();
            }
            this.ctx.beginPath();
            this.ctx.arc(x, y, r, 0, 2 * Math.PI);
            this.ctx.fillStyle = '#FF8000';
            this.ctx.fill();
        }
        // 恢复状态
        this.ctx.restore();
    },
    // 渲染时针
    renderHour: function(dateTime) {
        this.ctx.save();
        var hour = dateTime.getHours();
        var minute = dateTime.getMinutes();
        var second = dateTime.getSeconds();
        // 每秒6度
        var deg = ((hour % 12) * 30 * Math.PI / 180);
        
        // 计算分针和秒针旋转过的角度对应的时针旋转过的角度
        var otherDeg = ((minute * 6 + 6 / 60 * second) / 60 * 5) * Math.PI / 180;
        deg += otherDeg;
        this.ctx.rotate(deg);
        this.ctx.beginPath();
        this.ctx.moveTo(-15, 0);
        this.ctx.lineTo(90, 0);
        this.ctx.strokeStyle = '#0094ff';
        this.ctx.lineWidth = 8;
        this.ctx.stroke();
        this.ctx.restore();
    },
    // 渲染分针
    renderMiute: function(dateTime) {
        this.ctx.save();
        var minute = dateTime.getMinutes();
        var second = dateTime.getSeconds();
        // 每秒6度
        var deg = (minute * 6 * Math.PI / 180) + (6 / 60 * second * Math.PI / 180);

        this.ctx.rotate(deg);
        this.ctx.beginPath();
        this.ctx.moveTo(-20, 0);
        this.ctx.lineTo(120, 0);
        this.ctx.strokeStyle = '#333333';
        this.ctx.lineWidth = 5;
        this.ctx.stroke();
        this.ctx.restore();
    },
    // 渲染秒针
    renderSecond: function(dateTime) {
        this.ctx.save();
        var second = dateTime.getSeconds();
        // 每秒6度
        var deg = second * 6 * Math.PI / 180;

        this.ctx.rotate(deg);
        this.ctx.beginPath();
        this.ctx.moveTo(-30, 0);
        this.ctx.lineTo(150, 0);
        this.ctx.lineWidth = 2;
        this.ctx.strokeStyle = '#FF6666'
        this.ctx.stroke();
        this.ctx.restore();
    },
    render: function(dateTime) {
        this.ctx.save();
        this.ctx.lineCap = 'round';
        this.ctx.clearRect(0, 0, this.width, this.height);
        this.ctx.beginPath();
        this.ctx.translate(this.width / 2, this.width / 2);
        this.ctx.rotate(-Math.PI / 2);
        this.renderClock();
        this.renderScale();
        this.renderHour(dateTime);
        this.renderMiute(dateTime);
        this.renderSecond(dateTime);
        this.renderPoint();
        this.ctx.restore();
    }
}

var clock = new Clock();
clock.render(new Date());
setInterval(function() {
    clock.render(new Date());
}, 1000)