How do I create GUI from sprite atlas?

First up, hi everyone, it's my first post here at Scirra forums, although I've been using the game engine for more than a month now.

That being said, I'm developing my first mobile game (tbh, first game of any kind) and I want to optimize the performance from the start. While I was working on a sprite font for my game, I thought that it would be most efficient to have 1 spritesheet for user interface elements as well.

Problem here is that I'm not sure how this is done for elements with very different sizes or if I should do it at all. I think I read something about Construct 2 automatically sprite sheeting some stuff at export, correct me if I'm wrong. In that case, should I just have seperate image for every UI element, without worries about it crippling the perfomance on mobile?

Thanks ~

It's easiest to use separate images but you can get smart with re-using images at different sizes to good effect. For a really good example I'd recommend you check out this blog entry then scroll down to the heading that says "Example: Rayman Origins".