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();     }