这周在学canvas，就写了个时钟练习练习

window.onload = function(){
				
				var Timer = function(canvas_id){
					
					this.canvas = document.getElementById(canvas_id);
					this.ctx = this.canvas.getContext('2d');
					this.width = this.canvas.width;
					this.height = this.canvas.height;	
									
				};
				
				
				Timer.prototype = {
					
				
					
					draw:function(){
						
						this.ctx.save();
						this.ctx.translate(0,0);
						this.ctx.clearRect(0,0,this.width,this.height);	
						this.drawBackground();
						this.drawClock();
						this.drawClockPoint();
						this.ctx.restore();
										 
						
						
					},
					
					drawBackground:function(){
						
						this.ctx.globalAlpha  = 0.5;
						this.ctx.fillStyle = 'blue';
						this.ctx.fillRect(0,0,this.width,this.height);
						
					},
					
					drawClock:function(){
						
						
						//move to center
						this.ctx.translate(this.width/2,this.height/2);
						
						
						//inner arc
// 	
						this.ctx.fillStyle = '#333333';
						this.ctx.beginPath();
						this.ctx.arc(0,0,(this.width)/20,0,Math.PI*2,true);
						this.ctx.fill();
// 						
						//outer arc
						this.ctx.fillStyle = 'yellow';
						this.ctx.beginPath();
						this.ctx.arc(0,0,(this.width/2),0,Math.PI*2,true);
						this.ctx.fill();
						
						// Outer arc line
						for(var i=0;i<60;i++){
							this.ctx.save();
							this.ctx.rotate(Math.PI*2/60*i)
							this.ctx.beginPath();
							if(i % 5 == 0){
								this.ctx.moveTo((this.width/2.5),0);
							}else{
								this.ctx.moveTo((this.width/2.2),0);
							}
							
							this.ctx.lineTo(this.width/2,0)
							this.ctx.stroke();
							this.ctx.restore();
						}
						
						
					},
					
					drawClockPoint:function(){
						var currentDate = new Date();
						var hour = currentDate.getHours();
						var minute = currentDate.getMinutes();
						var second = currentDate.getSeconds();
						
						
						// alert(second);
						
						//画秒钟
						this.ctx.save();
						// this.ctx.fillStyle = 'black';
						this.ctx.rotate(Math.PI*2/60*second - Math.PI/2)
						this.ctx.beginPath();
						this.ctx.moveTo(0,0);
						this.ctx.lineTo(this.width/2,0);
						this.ctx.stroke();
					    this.ctx.restore();
					    
					    
					    //画分钟
						this.ctx.save();
						// this.ctx.lineWidth=5;
						this.ctx.fillStyle = 'black';
						this.ctx.rotate(Math.PI*2/60*(minute+second/60)  - Math.PI/2)
						this.ctx.beginPath();
						this.ctx.moveTo(0,0);
						this.ctx.lineTo(this.width/3,0);
						this.ctx.stroke();
					    this.ctx.restore();
					    
					    
					    //画时钟
						this.ctx.save();
						// this.ctx.lineWidth=10;
						this.ctx.fillStyle = 'black';
						this.ctx.rotate(Math.PI*2/12*(hour+minute/60+second/3600) - Math.PI/2)
						this.ctx.beginPath();
						this.ctx.moveTo(0,0);
						this.ctx.lineTo(this.width/3.5,0);
						this.ctx.stroke();
					    this.ctx.restore();
					    
					    
					    
						
					}
					
					
					
					
				};
					
					
				
			 var timer = new Timer('canvas');
			 timer.draw();
			 
			 function run (){
			 	timer.draw();
			 }
			 
			 window.setInterval(run,1000);
			 
				

	
				
			}

?页面代码

很短到一句

<canvas id='canvas' width='200' height='200'></canvas>

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