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Levels and XP

Levels and the XP curve

Levels start at 1. Going from level L to L + 1 costs round(base_xp × L ^ exponent) XP. The default curve (base_xp 50, exponent 1.5) makes early levels fast and the last ones long:

Level up XP it costs
1 → 2 50
10 → 11 1,581
99 → 100 49,252
1 → 100 in total 1,975,061

Overriding a curve from a data pack

A data pack can replace any profession's curve, so server owners rebalance without a recompile. The file for the profession <namespace>:<path> sits at data/<namespace>/professions/<path>.json:

{ "base_xp": 40, "exponent": 1.4 }

Levels follow the curve, XP stays

Only XP is saved; the level is computed from it. Changing a curve, then running /reload, moves every player's level at once, and their XP is untouched.

Server settings: curves and XP multipliers

Since 2.7.0. A server admin sets the professions' XP in the world's serverconfig/akumalib-server.toml, next to professionMode, with no data pack:

[professions]
    xpMultiplier = 1.0
    curves = ["inocruise:fisher = 20, 1.25, 1", "inocruise:cook = 20, 1.25, 1"]
    curvesAsShipped = ["inocruise:fisher = 20, 1.25, 1", "inocruise:cook = 20, 1.25, 1"]
Setting Meaning
xpMultiplier multiplies the XP gained in every profession: 2.0 levels twice as fast, 0.5 half as fast
curves one line per profession: "<id> = <base_xp>, <exponent>, <xp_multiplier>". The last number multiplies that profession's XP on top of xpMultiplier, and may be left out
curvesAsShipped written by the library, not to be edited: see below
  • Every installed profession is listed when the server starts, with the curve its mod or a data pack gives it, so an admin only changes numbers.
  • The config comes first, then the data pack, then the code.
  • A line nobody changed follows its mod. curvesAsShipped keeps what each line said when the library wrote it. A line that still says that is rewritten when its mod's curve changes in an update, or a data pack's on /reload. A line the admin changed is never touched. To get the mod's curve back, delete the line.
  • A line that cannot be read is logged at start and left as it is, for the admin to fix. Two lines for one profession: the later one is used, and that is logged too.
  • Curves too steep for the numbers (an exponent of 9 or 10 reaches past what a long holds by level 100) are capped rather than wrapped round.
  • The multipliers apply in AkumaProfessions.addXp, before ProfessionXpEvent. A fraction becomes a chance of one more point, so 1 XP at 0.5 gives 1 point half the time. setXp and setLevel, the admin writes, are not multiplied.

What a death costs

Since 2.10.0. Two more settings in the same section decide what a player's professions lose when they die:

[professions]
    deathXpLoss = "KEEP"
    deathXpLossPercent = 10.0
deathXpLoss On death
KEEP (default) nothing is lost
PERCENT deathXpLossPercent (0 to 100) of every profession's total XP, rounded to the point: levels can go down
ALL every profession goes back to 0 XP, level 1
  • Only a death costs anything: coming back from the End rebuilds the player too, and never loses XP.
  • Only XP is lost. The profession a Crew player chose, the recipes learned from a recipe item and the recipes already crafted are kept.
  • Levels follow the XP, and so do the titles a profession gives at a level: a player who drops below it stops holding that title until they climb back.
  • The player is not told: the professions book shows the new levels.
  • In code: DeathXpLoss, applied in the PlayerEvent.Clone handler after the profession data is copied over.

For a modpack

Put the file in the pack's defaultconfigs/ folder and every new world starts with it.

Restart the world after editing

Edit the file while the world is closed. Forge can reload a server config edited while the server runs, but that was not seen to happen in testing, so do not count on it.

Reading and granting XP

Everything goes through AkumaProfessions:

// server side, when a fish is caught
AkumaProfessions.addXp(serverPlayer, MyProfessions.FISHER.get(), 25);

// either side
int level = AkumaProfessions.getLevel(player, MyProfessions.FISHER.get());
ProfessionProgress progress = AkumaProfessions.getProgress(player, MyProfessions.FISHER.get());
Method Side Does
getLevel, getXp, getProgress both read the player's standing. On the client, the values come from the last sync
addXp(ServerPlayer, Profession, long) server grants XP, fires the events, syncs; returns the XP actually added
setXp, setLevel server admin writes: no event fires
sync(ServerPlayer) server resends the player's progress. The library already does it on login, respawn, dimension change, /reload and every write

ProfessionProgress holds level, totalXp, xpIntoLevel and xpForNextLevel (0 at the max level), which is what a progress bar needs.

The client has no curves

The client never computes a level: it only knows what the server last sent, for the local player. Reading another player's professions on the client returns level 1.

Events

Both fire on the Forge event bus, server side.

Event When Use it to
ProfessionXpEvent before addXp applies change the amount (an XP multiplier), or cancel the grant. Cancelable
ProfessionLevelUpEvent after addXp raised the level react to a new level. One grant can jump several levels: compare getOldLevel() and getNewLevel() 
@SubscribeEvent
public static void onProfessionXp(ProfessionXpEvent event) {
    if (event.getProfession() == MyProfessions.FISHER.get() && hasFishSoupBuff(event.getEntity())) {
        event.setAmount(Math.round(event.getAmount() * 1.15));
    }
}