iPhone HUD style progress bar

I've been wanting to create a HUD style loading bar like the SMS app on the iPhone used to have but I don't know how to. I was wondering if anyone has done this before or if there is a tutorial somewhere for it? I just think it looks so nice and w开发者_StackOverflow社区ould like to use it rather than the built in loading progress bar.

It should be very simple to implement using Core Animation layers (the CALayer class).

The bar would be a layer with rounded corners and the fill could be drawn by a custom drawing method.