var canvas,board,img;
			 canvas = document.getElementById('myCanvas');
			 img= document.getElementById('img');
			
			 canvas.height = 300;
			 canvas.width = 500;
			
			 board = canvas.getContext('2d');
			
			 var mousePress = false;
			 var last = null;
			function beginDraw(){
			 mousePress = true;
			}
			
			 function drawing(event){
			event.preventDefault();
			if(!mousePress)return;
			 var xy = pos(event);
			if(last!=null){
			board.beginPath();
			board.moveTo(last.x,last.y);
			board.lineTo(xy.x,xy.y);
			board.stroke();
			}
			 last = xy;
			
			}
			
			 function endDraw(event){
			 mousePress = false;
			 event.preventDefault();
			 last = null;
			}
			
			 function pos(event){
			 var x,y;
			if(isTouch(event)){
			 x = event.touches[0].pageX;
			 y = event.touches[0].pageY;
			}else{
			 x = event.offsetX+event.target.offsetLeft;
			 y = event.offsetY+event.target.offsetTop;
			}
			// log('x='+x+' y='+y);
			 return {x:x,y:y};
			}
			
			 function log(msg){
			 var log = document.getElementById('log');
			 var val = log.value;
			 log.value = msg+'n'+val; 
			}
			
			 function isTouch(event){
			 var type = event.type;
			if(type.indexOf('touch')>=0){
			 return true;
			}else{
			 return false;
			}
			}
			
			 function save(){
			//base64
			 var dataUrl = canvas.toDataURL();
			 //document.getElementById('textId').innerText(dataUrl);
			// document.getElementById("textId").innerHTML = dataUrl; 
			// dataUrl = dataUrl.replace("image/png","image/octet-stream");
			 //img.src = dataUrl;
         alert(dataUrl)
			}
			
			
			 function clean(){
			board.clearRect(0,0,canvas.width,canvas.height);
			
			}
			
			 board.lineWidth = 1;
			board.strokeStyle="#0000ff";
			
			
			 canvas.onmousedown = beginDraw;
			 canvas.onmousemove = drawing;
			 canvas.onmouseup = endDraw;
			canvas.addEventListener('touchstart',beginDraw,false);
			canvas.addEventListener('touchmove',drawing,false);
			canvas.addEventListener('touchend',endDraw,false);