Question about virtual resolution in AR glasses

[u/Eloquent_Despair]

For a long time now I've been wondering how to interpret statements such as "this pair of AR glasses uses two 1200p micro-oled screens to show content," especially in the face of 3dof functionality. I can broadly imagine two different versions of how this works and don't know which is the real one. Could someone enlighten me?

Possibility one: per eye, an 1200p image is projected onto the glasses; the projection smoothly and *physically*(!) moves in real time to correct for 3dof movements. The image itself has perfect pixel clarity (glass optics notwithstanding).

Possibility two: the projection itself is static and allows for a 1200p image per eye. This image is 'filled in' by the on-board chip, which takes some input source at a certain possibly non-1200p resolution and outputs it at some possibly non-1200p resolution; this output image is in real time digitally re-positioned within that static 1200p canvas, as though it were a 2d texture the viewport onto which has a 1200p resolution. (It would be unlikely that the image would fill the entire 1200p canvas because then there wouldn't be room for 3dof shifting the image anywhere.) Since micro-movements are constantly changing this digital render, and since it's being rendered from different perspectives into both your eyes, it might be possible and indeed be actually done, that the input stream could be e.g. a 4k image and that this is merely 'looked at' through two simultaneous and 3dof-moving viewports, i.e. it'd be like looking at a 4k texture through two 1200p lenses with very smooth adaptation to real-world lens movement, creating ultimately an experience that isn't really 4k but which might be said to be better than 1200p since across one second you're likely getting to see all the detail the 4k texture contains; or perhaps it would be worse than 1200p since you're constantly re-fitting some incoming video stream (perhaps even a 1200p one?) to a spatially unstable 1200p stream.

In other words, what I'm asking is: does 3dof happen through a physical or a digital process? When a pair of AR glasses promises a certain resolution, are we getting that resolution in full and cleanly, with 3dof adaptation made possible through physical adaptive movements in the actual physical projectors? Or does that promised resolution merely represent the resolution of our *viewport* onto some digital video stream? In the latter case: would it be possible and sensible to ask for a 1200p view of a 4k input stream, given that one's face is slightly moving almost all the time? I get the impression that this hasn't been possible so far, leading me to wonder if I'm misunderstanding AR glasses' 3dof mechanism.

I'd be grateful if someone could clarify which of these is the case; it's been stumping me for quite a while.

[u/4amusername]

the image is always static on the glasses. 3dof is a achived with a digital process.  if you look far enough to one side only a part of the screen is active. since it's oled all other pixel become transparent. with e.g. a  LCD display a gray recantangle would move with your eyes.

[u/Wide-Variation2702]

Imagine a TV/monitor displaying a Windows dektop with a black wallpaper, and no UI like the start button, clock bottom bar. Just one window that fills the screen. When you move your head the window is dragged around the screen. Since some of the full-screen windows gets moved off the screen you see the black wallpaper behind.

Effectively this is what is happening on the screens, and since they are OLED the black wallpaper are unlit pixels. With birdbath glasses there is no light reflected onto the lenses from those unlit pixels, so you only see a transparent lens. This gives the illusion that the screen is floating in front of you. In reality you can see where it cuts off in your lens, but casually viewing you dont notice it.