I've used my environment (with added main menu) to start creating an imageset file:
Thanks to proper planning this time, all the dimensions are nice round multiples of 10 pixels and everything is spaced out, so there shouldn't be any weird image clipping and everything should fit together properly! Even the icons are positioned in imaginary boxes 40 by 40 pixels to make moving them about easier. My initial layouts above were all blocky because I knew I'd arrive at this point needing some structure.
I've written an imageset text file. The only difficult element so far is the lower bar. For it to match the screen properly it'll need to stretch, so if the entire thing were recorded as a single image the angles of the corners would break and not match with the corners they have to fit into. Instead I've chopped it into three, the corners and the rectangular centre, with the centre stretching as needed. I hope that works properly in-game.
I'd like to be able to test this in-game soon, which will also require layout files. However, if another Lua script links to an element which isn't there (which will be the case since I'm removing all the old stuff) CEGUI throws a fit, so I need some way to disable pretty much every GUI-related function. @Moopli do you know any way of doing this?