js基于canvas实现时钟组件

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这篇文章主要介绍了js基于canvas实现时钟组件的方法,帮助大家更好的理解和使用JavaScript,感兴趣的朋友可以了解下

canvas一直是前端开发中不可或缺的一种用来绘制图形的标签元素,比如压缩上传的图片、比如刮刮卡、比如制作海报、图表插件等,很多人在面试的过程中也会被问到有没有接触过canvas图形绘制。

定义

canvas元素用于图形的绘制,通过脚本 (通常是JavaScript)来完成。
canvas标签只是图形容器,您必须使用脚本来绘制图形。

浏览器支持

Internet Explorer 9、Firefox、Opera、Chrome 和 Safari 支持

那么本篇文章就通过一个时钟组件来熟悉使用一下关于canvas的api。

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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>canvas时钟</title>
<style>
*{margin:0;padding:0;}
body{text-align:center;padding-top:100px;}
</style>
</head>
<body>
<canvas id="clock" width="200px" height="200px"></canvas>
<script>
(function(win){
    function DrawClock(options){
        this.canvas = options.el;
        this.ctx  = this.canvas.getContext('2d');//方法返回一个用于在画布上绘图的环境
        this.width = this.ctx.canvas.width;
        this.height = this.ctx.canvas.height;
        this.r   = this.width / 2;
        this.rem  = this.width / 200;
        this.digits = [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1, 2];
 
      var self  = this;
      self.init();
      setInterval(function(){
        self.init();
      }, 1000);
    }
 
    DrawClock.prototype = {
        init: function(){
            var ctx = this.ctx;
            ctx.clearRect(0, 0, this.width, this.height);  //在给定的矩形内清除指定的像素
            var now = new Date();
            var hours = now.getHours();
            var minutes = now.getMinutes();
            var seconds = now.getSeconds();
 
            var hour = hours >= 12 ? hours - 12 : hours;
            var minute = minutes + seconds / 60;
 
            this.drawBackground();
            this.drawHour(hour, minute);
            this.drawMinute(minute);
            this.drawSecond(seconds);
            this.drawDot();
            ctx.restore();
        },
        drawBackground: function(){
            var ctx = this.ctx;
            var self = this;
            ctx.save();
            ctx.translate(this.r, this.r);     //重新映射画布上的 (0,0) 位置
            ctx.beginPath();
            ctx.lineWidth = 8 * this.rem;
            ctx.arc(0, 0, this.r - ctx.lineWidth / 2, 0, 2 * Math.PI, false);  //创建弧/曲线(用于创建圆形或部分圆)
            ctx.stroke();
            ctx.font = 16 * this.rem + "px Arial";//设置或返回文本内容的当前字体属性
            ctx.textAlign = "center";       //设置或返回文本内容的当前对齐方式
            ctx.textBaseline = "middle";      //设置或返回在绘制文本时使用的当前文本基线
            this.digits.forEach(function(number, i){
                var rad = 2 * Math.PI / 12 * i;
                var x = Math.cos(rad) * (self.r - 33 * self.rem);
                var y = Math.sin(rad) * (self.r - 33 * self.rem);
                ctx.fillText(number, x, y);    //在画布上绘制"被填充的"文本
            });
 
            //分钟的刻度,每分钟转6deg
            for (var i = 0; i < 60; i++){
                ctx.save();            //保存当前环境的状态
                ctx.rotate(6 * i * Math.PI / 180); //旋转当前绘图
                ctx.beginPath();          //起始一条路径,或重置当前路径
                ctx.moveTo(0, -82 * this.rem);   //把路径移动到画布中的指定点,不创建线条
                ctx.lineTo(0, -87 * this.rem);   //添加一个新点,然后在画布中创建从该点到最后指定点的线条
                ctx.closePath();          //创建从当前点回到起始点的路径
                ctx.strokeStyle = '#000';     //设置或返回用于笔触的颜色、渐变或模式
                ctx.lineWidth = 1 * this.rem;   //设置或返回当前的线条宽度
                ctx.stroke();           //绘制已定义的路径
                ctx.restore();           //返回之前保存过的路径状态和属性
            }
            //小时的刻度,每小时转30deg
            for (var i = 0; i < 12; i++){
                ctx.save();
                ctx.rotate(30 * i * Math.PI / 180);
                ctx.beginPath();
                ctx.moveTo(0, -79 * this.rem);
                ctx.lineTo(0, -87 * this.rem);
                ctx.closePath();
                ctx.strokeStyle = '#000';
                ctx.lineWidth = 2 * this.rem;
                ctx.stroke();
                ctx.restore();
            }
        },
        drawHour: function(hour, minute){
            var ctx = this.ctx;
            ctx.save();
            ctx.beginPath();
            var hRad = 2 * Math.PI / 12 * hour;
            var mRad = 2 * Math.PI / 12 / 60 * minute;
            ctx.rotate(hRad + mRad);
            ctx.lineWidth = 6 * this.rem;
            ctx.lineCap = "round";         //设置或返回线条的结束端点样式
            ctx.moveTo(0, 10 * this.rem);
            ctx.lineTo(0, -this.r / 2);
            ctx.stroke();
            ctx.restore();
        },
        drawMinute: function(minute){
            var ctx = this.ctx;
            ctx.save();
            ctx.beginPath();
            var rad = 2 * Math.PI / 60 * minute;
            ctx.rotate(rad);
            ctx.lineWidth = 3 * this.rem;
            ctx.lineCap = "round";
            ctx.moveTo(0, 10 * this.rem);
            ctx.lineTo(0, -this.r + 26 * this.rem);
            ctx.stroke();
            ctx.restore();
        },
        drawSecond: function(second){
            var ctx = this.ctx;
            ctx.save();
            ctx.beginPath();
            ctx.fillStyle = "#c14543";
            var rad = 2 * Math.PI / 60 * second;
            ctx.rotate(rad);
            ctx.moveTo(-3 * this.rem, 20 * this.rem);
            ctx.lineTo(3 * this.rem, 20 * this.rem);
            ctx.lineTo(1, -this.r + 26 * this.rem);
            ctx.lineTo(-1, -this.r + 26 * this.rem);
            ctx.fill();  //填充当前绘图(路径)
            ctx.restore();
        },
        drawDot: function(minute){
            var ctx = this.ctx;
            ctx.beginPath();
            ctx.fillStyle = "#fff";
            ctx.arc(0, 0, 3 * this.rem, 0, 2 * Math.PI, false);
            ctx.fill();
        }
    };
 
    win.DrawClock = DrawClock;
})(window);
 
new DrawClock({el: document.getElementById("clock")});
</script>
</body>
</html>

只要心中有丘壑,就能耕出二亩田!canvas时钟用到了canvas中大部分的api,通过学习canvas时钟的代码实现,很能了解canvas的属性和方法,同时,实现时钟效果时,用到了数学中的几何模型正弦sin和余弦cos以及弧度的计算方法,又重温了一把当年学数学时的许多乐趣,可谓是一举两得。

时钟效果图如下:

js基于canvas实现时钟组件

以上就是js基于canvas实现时钟组件的详细内容,更多关于canvas实现时钟组件的资料请关注米米素材网其它相关文章!

原文链接:https://www.cnblogs.com/tnnyang/p/8951804.html