It's been asked before but title was not very precise, so maybe this will be better.
Basically, GUILayoutUtility.GetLastRect() return the rect in the current Area local coordinates, that is if you begin an area, draw a button and query for the last rect, you'll get x and y = 0. This is fine if you plan on drawing within that area, but this is very problematic if you want to compose something on top of everything, think tooltip. Hence the "need" to have an absolute rect definition of a gui so that at a later time in the OnGUI function, I can come back and add more stuff around a specific area ( mouseposition is not an option on that particula case unfortunatly)
Since the function should be self contained, it's difficult, impractical to query for the last rect on each parent area to compute back the absolute position.
Welcome any hack or proposal :)
Hopefully there is away,