最近通過各種渠道學習了下html5中的canvas元素,為了練練手就隨手寫了一個簡易的時鐘。時鐘本身不復雜,沒有使用圖片進行美化,下面就與大家分享一下具體的代碼:
這是最終實現的效果:
部分的啟發點來自於 http://developer.51cto.com/art/201503/467645.htm
html代碼:
<!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;
}
</style>
</head>
<body onload="main()">
<canvas class = "canvas" id="canvasId" width = '400' height = '400'></canvas>
</body>
js代碼:
var Clockbox = function(obj,width,height){
this.o = {
'dates':[], //時間
'obj':obj, //canvas對象
'width':width, //canvas寬度
'height':height, //canvas高度
'obj2d':obj.getContext('2d'), //2d對象
'wcolor':'#000000', //線條顏色
'scalewidth':30, //刻度長度
'msradius':(1/30)*Math.PI, //分秒的弧度
'hsradius':(1/6)*Math.PI, //時的弧度
'hourHandLength' : (width/5), /*時針長度*/
'minHandLength':(width/6*1.8), /*分針長度*/
'secHandLength':(width/20*8), /*秒針長度*/
'fontsize':30 //數字大小
}
var _this = this;
this.infn();
setInterval(function(){
_this.o.obj2d.translate(-_this.o.width/2,-_this.o.height/2);
_this.o.obj2d.clearRect(0,0,_this.o.width,_this.o.height);
_this.infn();
},1000)
}
Clockbox.prototype = {
infn:function(){
//表盤
var obj2d = this.o.obj2d;
var dates = new Date();
this.o.dates = [dates.getHours(),dates.getMinutes(),dates.getSeconds()];
//繪制
obj2d.beginPath();
obj2d.arc(this.o.width/2,this.o.height/2,this.o.width/2,0,2*Math.PI,false);
obj2d.strokeStyle = this.o.wcolor;
obj2d.stroke();
//刻度
this.scalefn(obj2d);
//時針
this.hour(obj2d);
//分針
this.minute(obj2d);
//秒針
this.sec(obj2d);
},
//繪制刻度和指針
scalefn:function(obj2d){
obj2d.translate(this.o.width/2,this.o.height/2);
for(var i = 0;i<12;i++){
obj2d.moveTo(this.o.width/2-this.o.scalewidth, 0);
obj2d.lineTo(this.o.width/2, 0);
obj2d.rotate(this.o.hsradius);
}
obj2d.font = "bold "+this.o.fontsize+"px impack";
obj2d.textAlign = "center";
obj2d.fillStyle = "#ff9000";
obj2d.fillText("12",0,-((this.o.width/2)-(this.o.scalewidth*2+10)));
obj2d.fillText("3",((this.o.width/2)-(this.o.scalewidth*2)),this.o.fontsize/3);
obj2d.fillText("6",0,((this.o.width/2)-(this.o.scalewidth*2)));
obj2d.fillText("9",-((this.o.width/2)-(this.o.scalewidth*2)),this.o.fontsize/3);
obj2d.stroke();
obj2d.restore();
},
//時針
hour:function(obj2d){
obj2d.save();
obj2d.rotate(this.o.hsradius*Number(this.o.dates[0]));
obj2d.moveTo(0,0);
obj2d.lineTo(0,-this.o.hourHandLength);
obj2d.stroke();
obj2d.restore();
},
//分針
minute:function(obj2d){
obj2d.save();
obj2d.rotate(this.o.msradius*Number(this.o.dates[1]));
obj2d.beginPath();
obj2d.moveTo(0,0);
obj2d.lineTo(0,-this.o.minHandLength);
obj2d.stroke();
obj2d.restore();
},
//秒針
sec:function(obj2d){
obj2d.save();
obj2d.rotate(this.o.msradius*Number(this.o.dates[2]));
obj2d.beginPath();
obj2d.moveTo(0,0);
obj2d.lineTo(0,-this.o.secHandLength);
obj2d.stroke();
obj2d.restore();
}
}
function main(){
var can = document.getElementById('canvasId');
var Clock = new Clockbox(can,400,400);
}
js代碼詳解:
1.首先這裡使用了面向對象的形式
2.這裡為了方便更改大小,傳入了3個參數 obj,width,height,分別表示canvas元素 以及它的寬度和高度,表盤的半徑是寬的二分之一
3. 因為1小時有60分鐘 所以每一個分鐘單元格應該有的弧度就是(1/(60/2))*Math.PI,小時同理
4. 依據現在的時間 用 .rotate()方法對指針做角度控制 12點的時針的弧度就是 一個小時的弧度*12
5.最後每秒不斷的清除畫布 重構 就形成了一個動態的時鐘
遇到的問題:
translate() 在畫完之後 canvas的原點並不在左上角了 ..... 最後在定時器重新設定解決了這個問題