C#

MyClass{
    // by default the fixed (x,y) coordinates are set to (0,0)
    private int _x = 0;
    private int _y = 0;

    // by default no line will be drawn
    private bool drawLineA = false;  
    private bool drawLineB = false;

   // should be called on each instance of the class to
   // set values for the fixed x and y parameters for the
   // draw line functions
   public void setInitialXY(int x,int  y)
   {
      _x = x;
      _y = y;
   }

   // helper function to demonstrate the concept
   private void  MyDrawLine(Graphics pg, int x,int y)
   {
        pg.DrawLine(_x,_y, x, y);
   }

   // the paint function examines the settings for each line
   // and draws the line if necessary. the values for x and y\
   // for each line have been picked arbitrary
   protected override void  OnPaint(PaintEventArgs pe)
   {
        if(drawLineA)
              MyDrawLine(pe.Graphics, 87, 67);
        if(drawLineB)
              MyDrawLine(pe.Graphics, 55, 94);
   }

    // the following two functions can be called on an instance of this class
    // to toggle the drawing of either of the functions
    //  a call to ToggleLineA/B can be made inside a button click event handler
   public void ToggleLineA()
   {
       drawLineA = !drawLineA;  // this toggles whether or not Line A is drawn
       this.Invalidate();       // after the change, make sure the object will be redrawn
   }

   public void ToggleLineB()   
   {
       drawLineB = !drawLineB;  // this toggles whether or not Line B is drawn
       this.Invalidate();       // after the change, make sure the object will be redrawn
   }
}

LineInfo a, b;<br />
<br />
ButtonA_Click(sender, e)<br />
{<br />
   a = new LineInfo(x1, y1, x2, y2);<br />
   Invalidate();<br />
}<br />
<br />
ButtonB_Click(sender, e)<br />
{<br />
   b = new LineInfo(x1, y1, x2, y2);<br />
   Invalidate();<br />
}<br />
<br />
protected override void OnPaint(Paint Event Args pe)<br />
{<br />
   if (a != null) a.Draw(g, pen);<br />
   if (b != null) b.Draw(g, pen);<br />
}