I would like to create a window which could float above the canvas and windows below it AND be able to see thru the floating window while that window contains a graph. The objective is to match the floating window's graph to the graphs below.

I kinda have an inkling of how to get it started but would like to get a skeleton from which I can expand once the floating window is established.
Anyone ever do this? And no this is not for a school project !!