Here I was hoping this would be something that works with the OS to take pre-window-compositor “3D screenshots” of a desktop, and then assigns the windows Z depths so that they’re floating above the desktop + each-other. Looking at the rendering of such a “3D screenshot” (in orthogonal projection) would look exactly like a regular screenshot… until you added a depth-of-field effect.

But, of course, you could also look at it in other projections; tilting it around in 3D space (as done here); applying fog to shadow “distant” windows; lighting the scene from a point-source so as to make the windows cast real shadows on one-another (with more light let through translucent areas!); etc. I would imagine that the (ideally HTML5 embeddable) viewer for this “3D screenshot” format would do all those things.

(I do hope someone does try creating such a “3D screenshot” format and viewer, as IMHO it would have a fairly-obvious use-case: reproducing static “look-around-able” snapshots of the already-depth-mapped AR window layouts in visionOS. Being able to tack arbitrary depth-maps onto windows from a 2D desktop OS would just be a bonus.)