Case study · iOS · Multiplayer
Four cards. Two looks. Lowest hand wins. The card game from the table, on the phones already in your pockets.
Black king: 30 points
What it is
Everyone gets four cards, face down, and may look at two of them once. After that you're on your memory, and so is everybody else.
It's the table game that goes by Magic, Cabo, Cambio or Golf depending on who taught you, played by the rules our table plays. One person starts a table and reads out a four-letter code, everyone else types it in, and the phones become the cards. No account, no sign-up, nothing saved. When you think you're lowest, call Magic. Be wrong, and you take thirty.
In the app
Engineering
Secrets
In a game built on hidden information, the obvious approach, sending the whole table to every phone and hiding what you shouldn't see, means anyone curious enough can read everyone's hand.
Instead each player gets their own version of the table with everything they aren't allowed to see removed, delivered on a private channel named by a secret only their phone holds.
Network
The phone that starts the table holds the one true game: it checks every move against the rules and tells everyone what happened. There's no game server to pay for or keep running.
That part was written so it could move to a real server unchanged, and so a full game can be played in a test with no network at all.
Speed
The moment a card lands in the middle, anyone holding the same rank can burn it, and the first tap wins. Burns chain onto burns, a wrong burn costs you cards, and burning someone else's card means handing them one of yours, face down, unseen by either of you.
Every one of those rules is covered by tests, including one that checks no card is ever created or lost, however strange the round gets.
Bots
Cards get fresh labels each round, so a label that meant a six last round can mean a three now. The practice players kept their memory between rounds and started confidently burning cards they had never seen.
Now they forget everything the moment a new deal arrives, just like people should.
Shipping
A multiplayer game needs several people, and an App Store reviewer is one person. The review notes link to a full walkthrough video of a real game.
Rule tweaks, card art and fixes go straight to phones without a new App Store submission. Players just reopen the app.
Testers and the public get updates on separate tracks, so a change can be tried on a few people before it reaches everyone.
Bots to learn against or fill an empty seat, so the game works even when only two of you showed up.
Built with
Next app
A party quiz for a room full of people, in English or Egyptian Arabic.