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VIII · The player

Verified against Minecraft 26.3 · Part VIII · The entity a human plays as: what it is made of, when it runs, and the five things it does that the rest of the world does differently.

Everything in Parts IV to VII happens to the world. This part is about the one object in it that argues back. You meet it as friction — the snap back after a laggy jump, the swing that does more damage if you wait, the food bar that empties from sprinting and not from walking, the effect timer that keeps counting while the connection is down — and every one of those is the same thing showing through. A player is an entity like any other, with the same base class, the same tick and the same synched data, and then almost every rule is bent for it: it is ticked twice instead of once, its inventory reports seven slots it does not store, its melee combat has three separate entry points of which the famous one is the least interesting, and the server simulates its movement in full every tick and then throws the answer away. The server is not allowed to be right about the player — nor about anything a player steers, which borrows the player’s authority — and this part is the cost of that.

The shape of the part

Part VIII is a trunk and four branches. Two pages say what a player is and when it runs; everything after them is one thing a player does, and they are independent of each other — except the spear, which is the sword swing’s sequel and should not be watched before it. The inventory has no lecture of its own and does not need one: Part VII stops at the slot, and the container those slots sit in is a section of player anatomy, because what is interesting about it is that seven of its forty-three slots are somewhere else. So the shape is a trunk of two pages, four branches that do not depend on one another, and one sequel — which is what the figure numbers.

flowchart TD
    PA["1 · Player anatomy — eight classes, forty-three slots"]
    TT["2 · The two-phase tick — when it runs, and what is thrown away"]
    IM["3 · Input to movement — walking, and being believed"]
    SS["4 · The sword swing — one integer, and a number rebuilt"]
    SP["5 · The spear — two more melee paths"]
    HE["6 · Hunger and experience — two bars the server owns"]
    SE["7 · Status effects — a list of things happening to you"]
    PA --> TT
    TT --> IM
    TT --> SS
    TT --> HE
    TT --> SE
    SS -- "its sequel" --> SP

The trunk and its four branches, numbered to the watch order: an arrow means the page below assumes the page above, and the four leaving the two-phase tick are independent of one another, so the labelled edge is the only order this part insists on beyond the trunk.

Before you start

Part VI is the hard prerequisite, and two of its pages in particular. Entity anatomy, because a player is a LivingEntity with three rungs added on the server and four on the client, and this part never re-teaches the base; and authority, because every page here rests on it — a Player is client-authoritative on both sides, and the server’s own answer for your movement is thrown away in favour of the number you sent it. If you watch one page from another part first, watch that one. Three more of Part VI’s are assumed rather than re-taught: attributes, because the reach and base numbers of an ordinary swing are attributes; synched entity data; and movement and collision, the pipeline input to movement feeds and never repeats.

Then the server tick and the level tick, because half this part’s timing claims are about which phase something ran in — including the fact that a player’s own physics run after every level has finished. Players and sessions owns how a ServerPlayer comes to exist at all, and how the session it belongs to ends. From Part VII, using an item, because the spear’s charge is an item you use and the meal in hunger and experience is that same machinery from the eater’s end.

Watch in this order

  1. Player anatomy — the vocabulary page: eight classes, two game-mode objects, forty-three slots. There is a rung between LivingEntity and Player — Avatar — with no instance state at all, shared with a posable dummy; and the main-hand item has no storage of its own, being the selected hotbar slot seen through the equipment container a horse also has.
  2. The two-phase tick — one player, one tick, twice. The connection records where you are, runs the whole physics pipeline, and then puts you back: the server keeps the velocity and throws the position away.
  3. Input to movement — W is pressed. A held movement key pressed and released between two ticks never happened, flooding the server with move packets makes the anti-cheat stricter, and the packet that reports your key presses cannot move you but can move a minecart.
  4. The sword swing — left-click on a pig. The attack packet carries one integer and the server rebuilds the rest, charging the hit against a cooldown twice in two different shapes — quadratically on the base damage, linearly on the enchantment bonus — and multiplying the mace’s fall bonus by the critical hit.
  5. The spear — the part’s most surprising lecture. Two components on one item: a stab whose packet has no target in it, and a charge whose damage comes from closing speed and which ignores the attack cooldown entirely.
  6. Hunger and experience — two bars the server owns outright. Walking costs exactly zero exhaustion; a full bar with saturation left heals up to eight times faster than one at eighteen; and the experience packet watches the total, so every mutation that moves only your level has to poison the last-sent value by hand.
  7. Status effects — the part’s closer, and its cleanest statement of the server/client split: the client runs none of an effect’s behaviour — it counts the effect down, draws it, and reads it for its own movement. The server corrects that countdown by testing whether the remaining duration divides by six hundred, so the periodic correction never reaches an infinite effect, whose duration is −1.

Watched as lectures, one and two are the pair to keep together, and four and five are the other pair. Six and seven can be watched in either order, or skipped and returned to.

Where the part stops

Part VIII is the smallest part of the book with a system in it (only Part I is smaller, and Part I is two pages about the program the rest run inside and what the book leaves out) — 32 files and 8,460 lines in world/entity/player, world/food, ServerPlayer and client/player — and the coverage question has an almost trivial answer here: 1% of the part’s lines are named on no page in the book. A player is a small object surrounded by large ones, so the interesting borders are not the ones inside these packages but the ones just outside them.

Upward, the part starts at Avatar rather than at Entity: Avatar sits in Part VI’s package and is explained here, beside the Mannequin — the posable dummy that shares the rung, and the reason the rung exists — and what a player inherits above it belongs to Part VI. Outward, it stops where the player stops being a player. How a hit is resolved once it lands is damage and death in Part VI; what your client is told about everyone else is what the client is told in Part IX; the ledger behind the block you already saw break is prediction and acknowledgement in Part X; drawing a player, its skin and its model parts is Part XI’s; and the chat session a ServerPlayer carries — the public half of message signing, the key itself never leaving the client — belongs to chat and signing. The two game-mode objects, ServerPlayerGameMode and MultiPlayerGameMode, are the sharpest border of all: this part says what they hold, and what they do with a block is Part V’s two click pages.

Three things a reader will look for here have no lecture. Two are declined: Hotbar, and the HotbarManager just outside these packages that keeps the nine saved creative hotbars, belong to the creative screen’s saved hotbars, which this book does not cover; and sleep is half-explained on purpose, with player anatomy naming the fields and the refusals a bed answers with while the everyone is asleep half — the night skip and the weather reset — belongs to the level tick. The third is simply missing, and is the one gap this part admits rather than declines: nobody explains the walk between those two halves — what one player lying down does over the hundred ticks of Player.SLEEP_DURATION that follow, and which of the two owners is driving during them.

Reference this part uses

Attributes, because reach, attack damage, attack speed, sweeping ratio and knockback are all attributes — and attack damage and knockback, two of those that decide what a hit is worth, are not synced to the client at all. Packets for the movement, attack and health packets by name. Data components for the components that make an item a weapon. Damage outside LivingEntity for what a swing meets when the target is not a living entity. Then game rules, level data and rules and diagram lanes.

Rules: names, never code · how the system works, not how the code reads · newest version only · every backticked name passes tools/verify_names.py.