I think geometry being euclidean or not is specifically about parallel lines, and the term "non-euclidean" is sightly misused for other kinds of spatial gimmicks. At least that's what I learned after watching several ZenoRogue videos (HyperRogue channel) :)
Euclidean geometry is an extremely precise geometry, and there is nothing wrong with calling any deviation from it "non-Euclidean". Since Euclidean geometry is a fairly specific point in geometry-space, the only real objection is that calling something "non-Euclidean" doesn't tell you much about what it is, but Euclidean geometry isn't a bad choice for a "default" geometry and at least it tells you it's not that. There is no requirement for it to be continuously curved in some spherical or hyperbolic manner to be "non-Euclidean". Even just permitting a single portal into an otherwise Euclidean geometry would utterly shred Euclid's Elements from top to bottom.
By my examination of the original postulates, not only would portals wreck the parallel line postulate, it in fact ruins 4 out of 5 of them, leaving only that a line can be continuously extended (and that line can still self-intersect, which may in fact violate the definition of a "line" and mean all 5 axioms are busted if you really dug in). It means it is no longer possible to draw a line between any two points (portals can shadow portions of the space such that some points are not connectible), cicles lose a lot of their properties that we rely on (imagine the unit circle, and a portal starting x = .5 and going straight up... they're no longer necessarily continuous), right angles may not be equal to each other any more (portals can change the apparent angles, or give two interpretations rather than one), and of course the parallel line doesn't hold. Putting portals into a geometry fairly comprehensively makes it non-Euclidean.
This feels a bit like saying that putting a wall in a room makes it non-euclidean since there's now a barrier in the way.
I know where you're coming from, but this is confusing geometry and topology. (Curvature vs. how the space is connected.)
(The original meaning is of course about breaking 5th postulate while all the others hold, showing that it was possible was a celebrated result in mathematics, while it is trivial to break the postulates in some arbitrary way.)
Here the geometry is very unusual. But using the existence of portals to define that seems insincere.
My listing of similar games:
- Grim Omens 3/5 - Revengate 4/5 - Dungeon Crawl Soup (on pc) 4/5 - The greedy cave 5/5 - Pathos 4/5
How to create a game using hyperbolic geometry? (2020) - https://news.ycombinator.com/item?id=36448270 - June 2023 (44 comments)
HyperRogue: A puzzle roguelike in a non-Euclidean world - https://news.ycombinator.com/item?id=26073813 - Feb 2021 (34 comments)
HyperRogue β a non-Euclidean roguelike - https://news.ycombinator.com/item?id=17432974 - June 2018 (38 comments)
HyperRogue β A non-Euclidean roguelike - https://news.ycombinator.com/item?id=9744353 - June 2015 (33 comments)
Of course, this is just your opinion, presented as an objective fact.
HyperRogue is one of the few roguelikes that I got sucked into. In comparison, I never "got" DCSS and despite several tries I always got bored immediately.
Brogue, on the other hand, is perfectly simple but perfectly well-executed, a five-ingredient recipe that lets every ingredient shine.
Is it?
(This is also true of the recall effect, for no reason stated by the ingame text. But then again, the ingame text never claims anything other than that you'll recall to a particular depth, as opposed to a particular place.)
[0]https://store.steampowered.com/app/2941710/Project_Silverfis...

HyperRogue, the non-Euclidean roguelike, is a mind-melting masterpiece -- Rock Paper Shotgun
Current version: 12.0 (Jun 3, 2021) - get here or play online
or buy it on Steam, itch.io, Google Play, or AppStore!
See the Gallery for the high quality images of all lands.
You are a lone adventurer in a strange world, where geometry does not work in the expected way. Gather as much treasure as you can before the nasty monsters get you. Explore about 50 different worlds, each with its own unique treasures, enemies, and terrain obstacles. Your quest is to find the legendary treasure, the Orbs of Yendor. Collect one of them to win! Or just ignore your quest and collect smaller treasures.
The twist is the unique, unusual geometry of the world: it is one of just few games which takes place on the hyperbolic plane. Witness a grid composed of hexagons and heptagons, straight lines which seem to be parallel, but then they diverge and never cross, triangles whose angles add up to less than 180 degrees, how extremely unlikely is it to reach the same place twice, and how the world seems to be rotated when you do return. All this matters for the gameplay. The game is inspired by the roguelike genre (although in a very minimalist way), works of M. C. Escher, and by puzzle games such as Deadly Rooms of Death.
With more space than anything Euclidean. The game dynamically generates new parts of the world as you move. No previous understanding of hyperbolic geometry is required -- actually, playing HyperRogue is probably the best way to learn about this, much better and deeper than any mathematical formulas. It is virtually impossible to get back to a place where you have been before, unless you go back exactly the same way. Show your true mastery of hyperbolic navigation by finding the Orb of Yendor, Holy Grail, rescuing the Prince(ss)!
72 lands (72 in the free version), each with unique theme, mechanics, graphics, terrain features, native monsters, treasure type, and magical Orb power. The ultimate Hyperstone Quest requires you to get 10 treasures in each of the lands!
In many ways, HyperRogue is closer to boardgames like Chess, than to mainstream computer games -- except that its "chessboard" is a hyperbolic plane, with randomly generated features. Enemies move predictably, and most can be killed simply by moving into them -- however, they could kill your character with a single attack too! Even though the game disallows you from making moves which would lead to this immediately ("check" in Chess), fighting large groups is still a challenge.
If you want even more challenge, you will get it easily, due to HyperRogue's difficulty/high score system. The more treasures you collect in a given land, the more monster chase you there. Collect 10 treasures in the given land to show the basic understanding of it, 25 treasures to show that you have mastered it, or go for even more! The game never ends, but it gets harder and harder.
Enable the shoot'em up mode, and the game is no longer turn-based or grid-based. Play together with your friend (shmup mode is recommended). Try the Euclidean, elliptic, or spherical modes, to see why the geometry matters, or enable the heptagonal mode to make the hyperbolic effects stronger. Try extra challenges such as the Yendor Challenge or the Pure Tactics Mode, or make the game look differently with the Hypersian Rug or Conformal mode. The recently added Orb Strategy mode emphasizes the resource management by giving you harder challenges while allowing you to use your limited magical powers in difficult situations.
HyperRogue has started as a small, weird technical experiment, but it turned out that hyperbolic geometry combined with basic roguelike rules makes for exceptionally great gameplay, even if you do not care about geometry! Further work improved the gameplay, but also turned HyperRogue into probably the most fully featured engine for truly non-Euclidean geometry in existence. Even if you do not care about roguelikes, roguelites and block puzzles, you can play the tutorial as an explorable explanation about hyperbolic geometry, use HyperRogue for research in applied hyperbolic geometry, or use the texture mode and vector graphics editor to create mathematical art. The possibilities are endless!
HyperRogue can be downloaded freely from this website, or bought on Steam or itch.io; the paid versions are updated more frequently and include social features such as achievements and leaderboards. There are also Android and iOS versions.
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