title: Draw a cross at the mouses location on a canvas, non persistently
body: <p>I have this bound to the mousemove event of my canvas:</p>
  
  <pre><code>function(e){        
      var contDiv = $('#current_system_map'); 
      var offset = contDiv.offset();
      x = e.clientX-offset.left;
      y = e.clientY-offset.top;
      context.beginPath();
      context.moveTo(0,y);
      context.lineTo(595,y);
      context.moveTo(x,0);
      context.lineTo(x,595);
      context.strokeStyle = "rgb(255,255,255)";
      context.stroke();   
  }
  </code></pre>
  
  <p>and it works fine, to a point. The drawn cross is persistent, so when the mouse moves a new cross is drawn but the old one remains. I've tried essentially re-drawing the canvas but that cause the cross to be laggy and remain quite away behind the mouse.</p>
  
  <p>So i need to know how to draw the cross and make it dis-appear without having to re-draw everything on the canvas</p>