title: Radius doesn't decrease
body: <p>Here's my script: <a href="http://jsfiddle.net/VDC5h/" rel="nofollow">http://jsfiddle.net/VDC5h/</a></p>
  
  <pre><code>var xStart;
  var yStart;
  var xStop;
  var yStop;
  var i=0;
  var d=0;
  $('#obrazek').click( function(e) {
      if(i==1)
      {
          i=2;
      }
      if(i==0)
      {
          var posX = $(this).offset().left, posY = $(this).offset().top;
          xStart=(e.pageX - posX);
          yStart=(e.pageY - posY);
          i=1;
      }
  });
  $("#obrazek").on( "mousemove", function(e) {  
      if(i==1)
      {
          var posX = $(this).offset().left, posY = $(this).offset().top;
          xStop=(e.pageX - posX);
          yStop=(e.pageY - posY); 
          d=Math.sqrt(Math.pow(xStart-xStop,2)+Math.pow(yStart-yStop,2))
          $('canvas').drawArc({
              fillStyle: '#000',
              x: xStart, 
              y: yStart,
              radius: d
          });
          $('#d').html(d);                                
      }
  });
  </code></pre>
  
  <p>It works, but I can't reduce the radius. The radius only increases. On the bottom is "d". "d"=radius. When "d" decreases, radius doesn't decrease.</p>
  
  <p>Where is my mistake?</p>