creating elaborate window decorations using titlebars and gears.shape

[mimuki]

I'm hoping to eventually create the look of a more "3D" window decoration, and from what I've gathered so far, the process would be "draw 4 titlebars, and draw shapes on those titlebars as their background".
(Here's an example of what I mean when I say 3D- there's a shadow behind windows, and the borders use different shades of grey for shading)

buuut I've never really done anything like this before, and i've been struggling to make sense of the documentation. I would really appreciate some examples, even if its just "heres how you could check the client dimensions & draw a rectangle that wide"

[actionless]

you just define a template for the titlebar in a same way as for any other widget, here's my particular example for such sort of shadows:

https://github.com/actionless/awesome_config/blob/master/actionless/titlebar.lua#L580

i also remember @Elv13 was posting a link to much more compact examples of similar retro titlebars