Do you know anything about Prey 2017’s “looking glass”? Do you know if it involves any special techniques?

I know nothing about this stuff, but when I saw in-game I was really impressed. You can even break the screens into shards, and the little pieces still maintain the effect when they’re lying on the floor or flying through the air.

I've never played the game, but your description doesn't sound very hard to implement. Keep in mind there is no physical camera when rendering, so tricks like this become rather easy to implement. You just setup the camera appropriately and render the perspective being shown by the portal, transformed into view space, using an alpha mask to make sure it only draws pixels where the glass fragment is.

Isn't the more common usage of this in skyboxes? You'd have one area where the gameplay is taking place, then another area in the map that shows the larger scale area surrounding where the player is and the portal makes it appear that the gameplay area is within the other.

The designer needs to confine the player so they can't break the illusion (where Prey lets Morgan Yu shatter that 4th wall), or you can do things like put the player on a speeding train traveling through a scenery and falling off is fatal

I’m old. For me a skybox is what it says on the tin: a box with a fisheye texture that when rendered looks like a 360 panorama. Does the word mean rendering actual geometry now?

Marathon 2 by Bungie also had weird non-euclidean maps with overlapping sections in the late 90s I think.

I miss the customizability of that game. Early bungie works were up there with early blizzard or early valve. They sold a tool for fun instead of casting a bait for profit.

I recall that some of the developer commentary for either Portal or Portal 2 mentioned that they began level-development by using a special version of the namesake non-euclidean Portals to connect different chambers and hallways that were being developed in parallel.

Then, later in development, they ran a tool to stitch together all that geometry in a more-normal way, and they only had one case of impossible-overlap, which continued to use the non-euclidean link.

For those wondering where the impossible space is:

https://gaming.stackexchange.com/questions/20601/where-is-th...

I actually discovered this accidentally, because I found wheatley so damn annoying at this point, I was just noclipping through the levels to get to the next part of the game, and I couldn't noclip through that drop.

IIRC Duke3D also had a map where you had to walk a circular path twice to get back to where you started.

Duke3D used teleportation to simulate height, for instance in the beginning of the game when you drop down from the rooftop you actually teleport to a other part of the map.