Seeds and Determinism

In short

A run has one seed. Each system that needs randomness gets its own SeededRandom stream, made with SeededRandom.Derive(seed, streamId). Because streams never share an RNG, a shop reroll can never shift the pitches. Never renumber a stream id: it would change every seed’s run.

How it works

SeededRandom

• Wraps System.Random(seed). Methods: Value (0..1), Range(float, float), Range(int, int), NextSeed(), Pick(list), PickWeighted(list, weight).
• Derive(seed, stream) mixes two ints into a new seed with integer math only (identical on every platform):

x = (uint)seed ^ ((uint)stream * 0x9E3779B9)
x ^= x >> 16; x *= 0x7FEB352D; x ^= x >> 15; x *= 0x846CA68B; x ^= x >> 16
return x & 0x7FFFFFFF   // non-negative for System.Random

The streams in a run

What	Seed it uses	Where
The innings (pitcher per inning)	the raw run seed: new SeededRandom(seed)	RunState constructor, RunMapGenerator.Generate
One inning’s pitches	RoundSeed(node) = Derive(Derive(Seed, PitchStream = 1), node.index)	RunState.RoundSeed, passed in RoundContext.seed
Pitch type, location, speed	new SeededRandom(context.seed)	AtBatController builds PitcherAI
Special balls ($$$, Ghost…)	Derive(rng.Seed, BallStream = 0x0BA11)	PitcherAI constructor. Each pitch rolls the pitcher’s own ball first (PitcherDefinition.balls), then the park’s; a ball with an alternate (The Gale’s Headwind / Tailwind) draws once more for the 50/50.
The Phantom’s decoy balls	Derive(rng.Seed, DecoyStream = 0xDEC0)	PitcherAI.MakeDecoys
Which way a curveball / changeup loops	Derive(rng.Seed, ArcStream = 0xA2C)	PitcherAI.CreatePitch (arcAngle, only for arcSideways pitch types)
A hit’s spray spread and launch odds	new System.Random(context.seed ^ 0x6b1d), one per round	AtBatController.BeginRound (_hitRandom), passed to SwingResolver.FromContact (Batting Explained)
One shop visit’s offers and its rerolls	Derive(Derive(Seed, ShopStream = 2), visit)	RunState.CreateShopRng; ShopService.Open passes run.CurrentIndex as the visit
The daily map	Derive(DailySeed.Today, 0xDA11) % ballparks.Count	RunManager.DailyPark

Why shop rerolls can’t change the pitches

The pitch seed depends only on the run seed and the inning index. Buying, rerolling or the order of purchases draw only from the shop visit’s own RNG. The special-ball rolls, the decoys and the sideways loops also have their own streams, so none of them changes which pitch type comes next. The one exception is deliberate: where a special ball only rides some pitch types, PitcherAI leans on those types (FavouredShare = 0.8 of picks, capped at 3 in a row) using the main pitch RNG, so that lean is part of the pitch sequence itself (Pitching). Dev-menu forced pitches keep rolling as normal, so turning them off leaves the rest of the sequence unchanged.

Each shop visit starts a fresh RNG, so rerolls in one shop don’t change the first offers of the next.

Resuming a run

run.json stores only the seed, the player’s choices and totals (Save System). The innings, their pitches and the shop offers are rebuilt from the seed, so quitting in the shop resumes with the same offers, and quitting mid-inning replays that inning with the same pitches.

Daily seed

• DailySeed.Today = int.Parse(UtcNow "yyyyMMdd"), so everyone on the same UTC date gets the same seed. DailySeed.DateKey is "yyyy-MM-dd".
• The daily run is the seed’s map on Normal (StartDailyRun). It unlocks nothing.
• A daily checkpoint can only be resumed on its own date (RunSaveData.dailyDate).

Co-op

• The host picks a random seed with Random.Range(1, int.MaxValue) and sends it in StartRun with the batting order (Net Messages). Every player builds the same innings from it.
• TurnSeed(node, turn): turn 0 uses RoundSeed(node); later turns use Derive(RoundSeed(node), turn). So each turn of an inning faces its own pitch sequence (Co-op Rules).
• ShopSalt = LocalId + 1 on each player’s RunState. When it is not 0, the shop seed is salted again: Derive(shopSeed, ShopSalt). Each player sees their own offers; solo (ShopSalt = 0) is unchanged.

Numbers

What	Value	Where to tune
PitchStream	1	RunState (never renumber)
ShopStream	2	RunState (never renumber)
BallStream	0x0BA11	PitcherAI
DailyParkStream	0xDA11	RunManager
DecoyStream	0xDEC0	PitcherAI
ArcStream	0xA2C	PitcherAI
Hit random salt	0x6b1d (XOR with the round seed, not Derive)	AtBatController
Solo run seed	UnityEngine.Random.Range(1, int.MaxValue)	RunManager.StartRandomRun
Batting cage seed	UnityEngine.Random.Range(1, int.MaxValue) (not reproducible on purpose)	BattingCage

In the code

File	What it does
Scripts/Core/SeededRandom.cs	The RNG and Derive.
Scripts/Run/RunState.cs	Stream ids, RoundSeed, TurnSeed, CreateShopRng, ShopSalt.
Scripts/Run/RunMapGenerator.cs	Uses the raw seed to pick pitchers and bosses.
Scripts/Pitching/PitcherAI.cs	Pitch RNG plus the ball-effect, decoy and arc streams.
Scripts/Batting/AtBatController.cs	The per-round hit random.
Scripts/Upgrades/ShopService.cs	Draws offers and rerolls from the visit’s RNG.
Scripts/Progression/DailySeed.cs	Today, DateKey.

Gotchas

Same seed is not always the same shop

The shop draws from MetaProgression.UpgradePool(), the upgrades this player has unlocked. Two players on the same daily seed see the same innings and pitches, but different shop offers if their unlocks differ.

• Cosmetic randomness (scoreboard cracks, crowd waves, hat tumbles, blinks, the cutscenes’ handheld camera drift and fireworks) uses UnityEngine.Random on purpose: it never touches gameplay.
• The dev tools are not seeded: the insta-home-run spray and TEST HITS’ Random pick use UnityEngine.Random (Dev Menu and Shortcuts).
• Need randomness in a new gameplay system? Add a new stream id; don’t borrow another system’s RNG.
• Changing RunMapGenerator, PitcherAI or ShopService draw order changes what every existing seed produces, including saved runs and today’s daily. Between e7dba51 and 45a2167 this happened on purpose: RunMapGenerator now keeps every park’s own final boss out of the random boss pool (innings 3 and 6), and PitcherAI leans on special-ball pitches, so a seed from before gives different bosses and pitches now. Saved runs from before still load (RunSaveData version is unchanged) but replay differently.

Related

• Daily Seed and Leaderboard: the player side of the daily
• Pitching: what the pitch stream picks
• Shop and Economy: offers and rerolls
• Save System: the run checkpoint
• Co-op Rules: turns and the shared seed