code: function(from, to, canvas){
      var ctx = canvas.getCtx();
      ctx.beginPath();
      ctx.moveTo(from.x, from.y);
      ctx.lineTo(to.x, to.y);
      ctx.stroke();
    }
docs: /*
  Method: line
  
  Renders a line into the canvas.
  
  Parameters:
  
  from - (object) An *x*, *y* object with the starting position of the line.
  to - (object) An *x*, *y* object with the ending position of the line.
  canvas - (object) A <Canvas> instance.
  
  Example:
  (start code js)
  EdgeHelper.line({ x: 10, y: 30 }, { x: 10, y: 50 }, viz.canvas);
  (end code)