Smoothly Regrowing Energy Bar How Too ?

I have a energy bar that decrease with hits from 10 to 0. I have it so after a set amount of time it goes back to 10. How can I regrow the bar smoothly over that time instead of jumping to 10.
Thanks in advance, Jel
Thanks in advance, Jel
Comments
I use that heavily in my Spellcaster game.
http://oak.cats.ohiou.edu/~piccard/huwe/logarithm.jpg