C# drawing and invalidating 2 lines to meet

If i have 2 lines on a page as such:

   e.Graphics.DrawLine(blackPen, w, h, h, w);
    e.Graphics.DrawLine(blackPen, w2, h2, h2, w2); 
 

how would i animate the first line to reach the second line's position?

I have the following method which calculates the distance between two points (i'm assuming i would use this?)

   public int Distance2D(int x1, int y1, int x2, int y2)
    {
             //     ______________________
             //d = √ (x2-x1)^2 + (y2-y1)^2
             //
 
             //Our end result
             int result = 0;
             //Take x2-x1, then square it
             double part1 = Math.Pow((x2 - x1), 2);
             //Take y2-y1, then sqaure it
             double part2 = Math.Pow((y2 - y1), 2);
             //Add both of the parts together
             double underRadical = part1 + part2;
             //Get the square root of the parts
             result = (int)Math.Sqrt(underRadical);
             //Return our result
             return result;
     }
 

How would i re-draw the line (on a timer) to reach the second line's position? I've looked a lot into XAML (story-boarding) and such - but i want to know how to do this on my own. Any ideas? I know i would need a method which runs in a loop re-drawing the line after moving the position a tid bit. I would have to call Invalidate() in order to make the line appear as though it's moving... but how would i do this? how would i move that line slowly over to the other line? I'm pretty sure i'd have to use double buffering if i'm doing this as well... as such:

 SetStyle(ControlStyles.DoubleBuffer | ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint, true);
 

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