本文实例讲述了js+html5实现canvas绘制网页时钟的方法，画的是一个可用于网页的、带摆的钟表，可以通过按钮调整其大小和位置，具体实现内容如下
<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Clock</title><script type="text/javascript"> var xClock=300; //表心位置var yClock=250; //表心位置var d=180.0;//钟表圆面的半径var value = -d*1.07; function enlarge(){ d++;}function reduce(){ d--;}function westwards(){var c=document.getElementById("myCanvas");var g2d=c.getContext("2d"); g2d.translate(-1,0); //置坐标轴原点于表心 c=document.getElementById("myPendulum"); g2d=c.getContext("2d"); g2d.translate(-1,0); //置坐标轴原点于表心 }function eastwards(){var c=document.getElementById("myCanvas");var g2d=c.getContext("2d"); g2d.translate(1,0); //置坐标轴原点于表心 c=document.getElementById("myPendulum"); g2d=c.getContext("2d"); g2d.translate(1,0); //置坐标轴原点于表心}function upwards(){var c=document.getElementById("myCanvas");var g2d=c.getContext("2d"); g2d.translate(0,-1); //置坐标轴原点于表心 c=document.getElementById("myPendulum"); g2d=c.getContext("2d"); g2d.translate(0,-1); //置坐标轴原点于表心}function downwards(){var c=document.getElementById("myCanvas");var g2d=c.getContext("2d"); g2d.translate(0,1); //置坐标轴原点于表心 c=document.getElementById("myPendulum"); g2d=c.getContext("2d"); g2d.translate(0,1); //置坐标轴原点于表心} function fillPolygon( a, b, fillColor, ctx){ctx.beginPath();ctx.moveTo(a[0],b[0]);for (var j=1;j<a.length;j++)ctx.lineTo(a[j],b[j]);ctx.closePath();ctx.fillStyle=fillColor;ctx.fill();} function randomColor(){ var s ="#";for (var i=0;i<3;i++)s += Math.floor(Math.random()*16).toString(16);return s;} function locateCoordinate() {var c=document.getElementById("myCanvas");var g2d=c.getContext("2d"); g2d.translate(xClock,yClock); //置坐标轴原点于表心var c=document.getElementById("myPendulum");var g2d=c.getContext("2d"); g2d.translate(xClock,yClock); //置坐标轴原点于表心} function drawFace(){ //定义画钟表表面drawFace方法/* 表示1,2,4,5,7,8,10,11点钟位置的较小尺寸的菱形标志顶点坐标数组 */var x = new Array(0, Math.round(d/30), 0, Math.round(-d/30));var y = new Array( Math.round(-d*1.07),-d,Math.round(-d*0.9),-d);/* 表示3,6,9,12点钟位置的较大尺寸的菱形标志顶点坐标数组 */var x1= new Array(0,Math.round(d/15),0,Math.round(-d/15));var y1 =new Array(Math.round(-d*1.13),-d,Math.round(-d*0.9),-d);var c=document.getElementById("myCanvas");var g2d=c.getContext("2d"); //下面开始 准备画钟表圆面边 g2d.beginPath(); g2d.arc(0,0,d, 0 , 2*Math.PI); g2d.strokeStyle="lightGray"; g2d.lineWidth=d/18; g2d.stroke(); //最后一笔，画钟表圆面边 //下面开始准备画表示 每个钟点 的菱形 for (var i=0;i<12;i++) { //for 循环语句的循环体开始 if (i%3==0){ //画较大尺寸的红色菱形，表示3,6,9,12点 fillPolygon( x1, y1, "red", g2d); } else {//画较小尺寸的桔黄色菱形，表示其余的钟点 fillPolygon(x,y,"orange",g2d); }//以钟表表心为原点,坐标系顺时针转动30度,以便画下一个钟点位置的菱形标记 g2d.rotate(Math.PI/6.0); }//for 循环语句的循环体结束}//画钟表表面 drawFace 方法结束 /* 定义画钟表的时针、分针、和秒针的方法 drawNeedles* 形参 Hradian，单位弧度， 为时针从0点算起的弧度位置，* 形参 Mradian，单位弧度， 为分针从0分算起的弧度位置，* 形参 Sradian，单位弧度， 为秒针从0秒算起的弧度位置。*/function drawNeedles( Hradian, Mradian, Sradian ){var c=document.getElementById("myCanvas");var g2d=c.getContext("2d");//以钟表表心为原点,坐标系顺时针转动Hradian弧度,以便画出时针 g2d.rotate(Hradian); //表示时针的多边形顶点的坐标数组var Hx =new Array(0, Math.round(d/19),0, Math.round(-d/19) ); var Hy =new Array( Math.round(-d/2), Math.round(-d/3), 0, Math.round(-d/3) ); fillPolygon(Hx,Hy,"magenta",g2d);//时针设为紫红色,//以钟表表心为原点,坐标系逆时针转动Hradian弧度,以还原坐标系 g2d.rotate(-Hradian); //以钟表表心为原点,坐标系顺时针转动Mradian弧度,以便画出分针 g2d.rotate(Mradian);//表示分针的多边形顶点的坐标数组var Mx=new Array(Math.round(-d/19),0,Math.round(d/19));var My=new Array(0,Math.round(-d/1.3),0); fillPolygon(Mx,My,"gray",g2d); //分针设为灰色//以钟表表心为原点,坐标系逆时针转动Mradian弧度,以还原坐标系 g2d.rotate(-Mradian); //以钟表表心为原点,坐标系顺时针转动Sradian弧度,以便画出秒针 g2d.rotate(Sradian); // 秒针设为随机颜色 g2d.strokeStyle='green'; g2d.lineWidth="1"; g2d.moveTo(0,0); g2d.lineTo(0,Math.round(-d/1.1)); g2d.stroke(); g2d.beginPath(); g2d.arc(0,Math.round(-d),d/18, 0 , 2*Math.PI); g2d.fillStyle=randomColor(); g2d.fill(); //最后一笔，画秒针顶点的小球//以钟表表心为原点,坐标系逆时针转动Sradian弧度,以还原坐标系 g2d.rotate(-Sradian); } //画表针方法 drawNeedles的代码块结束 /* 画出字符串来表示瞬时时间 */function DrawTime() { var time=new Date(); //获取当前时间。 var hour=time.getHours(); //获取小时 var minute=time.getMinutes();//获取分钟 var second=time.getSeconds();//获取秒数 var apm="AM"; //默认显示上午：AM. var canvas =document.getElementById("myCanvas"); var g2d =canvas.getContext("2d"); if(hour>12){ //按照12小时制止显示 hour=hour-12; apm="PM"; } if(minute<10){ //如果分钟只有1位，补0显示 minute="0"+minute; } if(second<10){ //如果秒数只有1位，补0显示 second="0"+second; } g2d.clearRect(-xClock,-yClock,600,600); //清屏 var s = hour+":"+minute+":"+second+":"+apm; g2d.fillStyle="red"; g2d.font = d/4+ "px KAITI"; g2d.fillText(s,-d/1.8, d*1.4);g2d.font= d/4 + "px 楷体";// Create gradientvar gradient=g2d.createLinearGradient(0,0,canvas.width,0);gradient.addColorStop("0","magenta");gradient.addColorStop("0.5","blue");gradient.addColorStop("1.0","red");// Fill with gradientg2d.fillStyle=gradient;g2d.fillText("大数据",-d/2.6,d/2);//获得实例创建瞬间的秒读数,由此计算出秒针,相对于0 秒,走过的弧读数var c = Math.PI/30 * second; //获得创建瞬间的的分钟读数,由此计算出分针,相对于0 分,走过的弧读数var b = Math.PI/30 * minute;/* 获得创建瞬间的的钟点读数,由此计算出时针,相对于0 点,走过的弧读数。 * 时针走过的弧度为整点的度数(每小时走30度),加上走过分钟数的修正值 */var a = Math.PI/180*(30 * hour + minute/2);/* 坐标系平移 (xClock,yClock) ，使得坐标轴成为表盘中心 */ drawFace(); drawNeedles( a, b, c); } // 方法 DrawTime 的代码块结束 var i=0;function pendulum() { //pendulum_bobvar instantAngle = new Array(64,61,56,49,40,29,16,3,-8,-16,-29,-40,-49,-56,-61,-64,-64,-64,-61,-56,-49,-40,-29,-16,-8,3,16,29,40,49,56,61,64,64); //摆的即时角度数组var c=document.getElementById("myPendulum");var ctx=c.getContext("2d");var alpha=instantAngle[i++%instantAngle.length]*Math.PI/180;ctx.clearRect(-300,-300,900,900);ctx.rotate(alpha); // 秒针设为随机颜色 ctx.fillStyle='brown'; ctx.fillRect(-3,0,6,d*1.4); ctx.shadowBlur=20;ctx.shadowColor="black";ctx.fillStyle="blue";//ctx.fillRect(-d/3.5, d*1.35, d/1.6, d/4.4); ctx.font="40px 楷体";// Create gradientvar gradient=ctx.createLinearGradient(0,0,c.width,0);gradient.addColorStop("0","magenta");gradient.addColorStop("0.5","blue");gradient.addColorStop("1.0","white");// Fill with gradient//ctx.fillStyle=gradient;ctx.fillStyle="red"; ctx.fillText("大数据",-d/3.2,d*1.55);ctx.shadowBlur=0;ctx.shadowColor=null;ctx.fillStyle=null;ctx.rotate(-alpha); } function preparation(){ locateCoordinate() setInterval('DrawTime()',500); setInterval('pendulum()',200);} </script><style>#myCanvas{ z-index:3; position:absolute; left:0px; top:0px; }#myPendulum{ z-index:2; position:absolute; left:0px; top:0px;}#controlPanel{ position:absolute; left:600px; top:0px; width:100px; text-align:center; font-family:"楷体"; font-size:20px; font-weight:bold; color:#6C0;}</style></head><body onLoad="preparation()"><canvas id="myCanvas" > <p>Your browserdoes not support the canvas element!</p> </canvas><canvas id="myPendulum" > <p>Your browserdoes not support the canvas element!</p> </canvas><div id="controlPanel"><table><tr><td>控制</td><td>按钮</td></tr><tr><td><input value="增大" type="button" onclick="enlarge()"></button></td><td><input value="缩小" type="button" onclick="reduce()"></button></td></tr> <tr><td><input value="左移" type="button" onclick="westwards()"></button></td><td><input value="右移" type="button" onclick="eastwards()"></button></td></tr> <tr><td><input value="上移" type="button" onclick="upwards()"></button></td><td><input value="下移" type="button" onclick="downwards()"></button></td></tr></table> </div></body></html>效果图：
希望本文所述对大家的web程序设计有所帮助。