Discussion
Can somebody who knows Scala tell me how to mod lichess so I can add the DVD piece as a variant
https://suya.place/objects/7cba05a0-85a0-47e3-8bef-c63585412bcc
edit: lichess was the wrong thing, i wanted stockfish, and specifically fairy stockfish, but now we have a running version of dvd chess: https://neuromatch.social/@jonny/116898427723195466
there are all these custom weirdo piece notations and game variants but none of them seem to have a) autonomous pieces, which could be modeled as having a third player or multiple moves per move, b) restrictions on available moves based on prior movement history (the pawn 2->1, en passant, and castling history dependence seems to always be special-cased), c) pieces that change colors, d) pieces that are not allowed to move to specific squares. so what i want to do goes outside the usual boundaries of what stockfish considers "a piece" and doesn't fit neatly into its conception of what a "move" is. i think i might have to hack it together by dynamically switching the dvd piece between different base pieces and updating stockfish's state every turn manually. idk if that's possible, like if it's possible to express "black just moved twice, one normal move, and one bishop that is temporarily white, but the white player can't control it, and it will turn black again next turn and capture the piece right in front of it" to the engine, but there is apparently a neural net part of the engine so if i can express it then it might be possible for it to learn DVD strategy via RL.
basically i'm stuck between two choices: 1) either make a fullstack version so two people can play against each other, but then i have to host something and it would only be playable if someone else was on, or 2) hack the piece into a chess engine so it can be played vs. computer, but if the computer is just totally naive to the piece then it's not very fun either bc you'd win just by virtue of knowing the rules while the computer doesn't.
wait no this fairy stockfish does have turn side effects and piece ownership flipping. i think we might be in business.
dvd multiball madness
Stockfish does know how to capture the DVD and does seem to be able to predict that if it does nothing to avoid DVD then its pieces are taken. I have no idea if it is able to use DVD strategically or if it would ever choose to promote into DVD rather than a Queen. The value proposition of DVD is unclear because it gives you no special advantage to spawn it. Maybe it should stay being your color 2x as long if you spawn it. Idk I couldn't figure out a good way to write that. Its already 4 "pieces", one for each direction, maybe it needs to be 8, direction*who spawned it. Or 16, direction*turns until flip. Whatever. I choose DVD every time.
It is actually an interesting mechanic because nothing in chess has a 2-turn effect, so you need to think where and what DVD will be at a different speed than the other pieces, because it moves at the end of your move and your opponents move, and it can bankshot around and trap you pretty easily.
Only the king is a bumper so if your piece is in its way its only matter of time until it gets gotten. It forces you into awkward positions because you either have to waste a tempo cleaning up an environmental contaminant roving DVD or let it buzzsaw through your back line and hope it ricochets back at your opponent.
Only being able to sometimes control it is fun too. Stockfish I think is technically able to choose to slide the DVD when it can on the edges, but I haven't seen it do it. I have successfully used the side slide strategically to bend it back at my opponent.
I'll push tomorrow, gotta sleep. Its all wasm and vanilla js so I could throw it on a website and call it a day
alright everyone here is DVD chess: https://jon-e.net/dvd-chess/
i should add a switch that makes it so every dom element is resizeable and draggable instead of just the panels huh
shout out to stockfish which made it extremely easy to implement a custom dvd chess piece and then put the engine in wasm. i thought that would be about 10x as hard as it was, but since the fairy stockfish already had a bunch of variants with different hacks in there i could just diff fairy stockfish from regular and see where the different kinds of hacks live.
oh my god i just saw stockfish choose to move dvd, and it did it to threaten my knight in a way that makes sense. that rocks. still not sure if simulating automatic dvd moves makes it into its game state, but confirmed stockfish knows how to avoid, capture, and move dvd.
In line with chess NPCs, maybe you should be able to bribe DVD to go another way by giving it some of the pieces you captured. This saves your piece from being captured, and maybe reroutes it to capture your opponents piece, at the expense of spawning more DVDs. The characterization of DVD is a sort of borg-like, allegianceless horde who is only concerned with creating more DVDs
OK with a bit more reading I am convinced that stockfish simulates the correct series of possible moves for a DVD piece and thus should be on equal footing for strategic use by the algo. At first I was thinking there was no benefit to spawning a DVD, but it does have one powerful advantage, and that is doubling your moves. So if you were able to time the spawn and coordinate it with your other moves, it could be a powerful piece even without being under your direct control. You do actually have a decent bit of control over it at spawn because it can only be changed every so often, and only if its your color when it hits an edge, and it is costly to do. I did it lazily so the direction it goes after promotion is "towards the center" but I can fix that. I am going to simulate a bunch of games and see if the CPU ever chooses to spawn DVD over a queen. I doubt it will, but it might do so in some very specific conditions and I want to see what those are.
Oh wait, maybe I have to train the neural net on the variant to make it work real good. Oh well I have an old GPU at work that's mostly unused, so I guess that's next. I also want to try a few subvariants to see which of them causes the CPU to develop a DVD-centric playstyle
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