JavaScript html5 canvas实现图片上画超链接

<canvas id="canvasFile" style="margin-top:15px;" width="500" height="400"></canvas> 
<input type="button" id="btnRedo" value="Re-Draw" class="btn btn-warning"/> 

var photoW = 400; 
    var photoH = 300; 
    var photo; 
     
     
    // logic load image into canvas 
    // ... 
    // e.g.  
    // photo = new Image(); 
    // photo.onload = function() { 
    // draw photo into canvas when ready 
    // ctx.drawImage(photo, 0, 0, photoW, photoH); 
    // }; 
    // load photo into canvas 
    // photo.src = picURL; 
   
     
 // canvas highlight 
    var canvas = document.getElementById('canvasFile'), 
      ctx = canvas.getContext('2d'), 
      img = new Image; 
    var btnDone = document.getElementById('btnDone'); 
    var btnRedo = document.getElementById('btnRedo'); 
 
 
    ctx.strokeStyle = '#FF0000'; 
 
    function DrawDot(x, y) { 
      var centerX = x; 
      var centerY = y; 
      var radius = 2; 
 
 
      ctx.beginPath(); 
      ctx.arc(centerX, centerY, radius, 0, 2 * Math.PI, false); 
      ctx.fillStyle = 'red'; 
      ctx.fill(); 
      ctx.lineWidth = 2; 
      ctx.strokeStyle = '#FF0000'; 
      ctx.stroke(); 
    } 
 
 
    function startDrawing() { 
      ctx.drawImage(img, 0, 0, photoW, photoH); 
      canvas.onmousemove = mousemoving; 
      canvas.onmousedown = mousedownhandle; 
      canvas.onmouseup = mouseuphandle; 
      // ## mobile events 
      //touchstart – to toggle drawing mode “on” 
      //touchend – to toggle drawing mode “off” 
      //touchmove – to track finger position, used in drawing 
      canvas.addEventListener('touchmove', touchmove, false); 
      canvas.addEventListener('touchend', mouseuphandle, false); 
 
 
      btnRedo.onclick = function (e) { 
        ctx.clearRect(0, 0, ctx.width, ctx.height); 
        ctx.drawImage(photo, 0, 0, photoW, photoH); 
        savedrawing(); 
      } 
    } 
    function savedrawing(e) { 
      var image = document.getElementById('canvasFile').toDataURL("image/jpeg"); 
      image = image.replace('data:image/jpeg;base64,', ''); 
      $("#imgNric1").val(image); 
    }; 
 

    function mousemoving(e) { 
      if (drawing) { 
        mousedownhandle(e); 
      } 
    } 
 
 
    var drawing = false; 
 
 
    function mousedownhandle(e) { 
      drawing = true; 
      var r = canvas.getBoundingClientRect(), 
        x = e.clientX - r.left, 
        y = e.clientY - r.top; 
 
 
      DrawDot(x, y); 
    }  
 
    function mouseuphandle(e) { 
      savedrawing(); 
      e.preventDefault(); 
      drawing = false; 
       
    } 
  
 
    //// mobile touch events 
    function touchmove(e) { 
      if (e.clientX > 800) { 
        mousedownhandle(e); 
        return; 
      } 
 
      var r = canvas.getBoundingClientRect(), 
        //event.changedTouches[0].pageX + ":" + event.changedTouches[0].pageY; 
        x = e.changedTouches[0].pageX - r.left, 
        y = e.changedTouches[0].pageY - r.top; 
 
 
      DrawDot(x, y); 
      e.preventDefault(); 
    }