Fill a circle by values with onGUI

Hi, I want to have a bar which is gonna show the players XP. Simple enough. Although, if it's possible I'd like to have a circle that is 360* and if the players XP variable is at 50 it's gonna show half the texture, 180* to be exact. How would I do this? I guess I need to have some images but if it's a way I don't need to have 360 images it would be great!

Thank you!