VI · Entities

Verified against Minecraft 26.2 · Part VI · Everything in the world that is not a block: what one is, who is allowed to move it, how it is described to the other side, and how it stops.

Part V was about a position in a chunk section changing its mind. This part is about everything that is not in the grid — the zombie, the arrow, the boat, the dropped pickaxe, the invisible marker a data pack left as a bookmark. They share one base class that is deliberately thin on behaviour, one numbered array for telling clients about themselves, one bag of named numbers, one collision resolver and one abstract method for being hurt. A player recognises the part by the things that seem inconsistent about it: a mob glides where your own movement is crisp, a sheared sheep changes on every screen at once, a mob you named never despawns, and a hit that lands during the red flash does nothing at all. Every one of those is the same question in a different costume — which of the two programs is allowed to decide this?

The shape of the part

Part VI is a ladder. Each page needs the one below it and nothing above it, and the second rung is the one everything else leans on.

flowchart BT
    A["Entity anatomy — what an entity is"]
    B["Authority — who is allowed to simulate it"]
    C["Entity lifecycle — how it enters a world and leaves one"]
    D["Synched entity data — the channel that describes it"]
    E["Attributes — the named numbers it carries"]
    F["Movement and collision — what it does"]
    G["Goals and brains — why it does it"]
    H["Pathfinding — how a decision becomes a direction"]
    I["Damage and death — how it stops"]
    A -- "one type, one factory, one live object" --> B
    B -- "and one side of each pair does the arithmetic" --> C
    C -- "now it is in a world, findable and ticking" --> D
    D -- "one of six channels that describe it" --> E
    E -- "gravity, step height, speed: the physics knobs are attributes" --> F
    F -- "something has to set xxa and zza" --> G
    G -- "a decision is only a position until something walks there" --> H
    H -- "and everything above can be ended by one abstract method" --> I

One dependency runs forward instead of back, and it is Part X’s rather than this part’s: the client level opens by saying it is not an authority either, which only lands once authority has said what one is. So this part is watched first, and nothing here waits on Part X.

Before you start

The level tick, because half this part’s surprises are claims about which phase something ran in — the entity phase runs after the phase that broadcasts entity changes, and that one ordering explains why an attribute change is a tick late while a sheep sheared out of the packet queue, before the tick proper, is not. Tickets and loading, because whether an entity ticks at all is a property of the chunk it is standing in — for everything except a player, which is exempt — and chunk anatomy for the heightmaps that decide where a mob may spawn. Points of interest, because a villager’s whole day is claims on them and goals and brains draws PoiManager as a lane rather than explaining it. Blocks and states for the shapes that entities collide with, and Part IV’s scheduled ticks is not needed — entities keep no appointment book.

One more Part IV page, for one lecture: environment attributes and timelines before goals and brains. A villager’s schedule is a data-pack Timeline looked up at a position, and this part asks that system a question rather than teaching it.

Watch in this order

1. Entity anatomy — one EntityType from the registry, through a factory, to a live object the level ticks. The registry’s default is a pig, and that default reaches the network and never reaches your save file.
2. Authority — a zombie, a player and a boat each take one step on both sides. The client runs no physics at all for the mob chasing you, and the server runs your own player’s physics every tick and then overwrites the answer with a number you sent it.
3. Entity lifecycle — a zombie appears in the dark, is ticked for a while, and is either forgotten or written to disk. The spawner rolls one height per category per chunk per tick, so caves and the open field compete for the same slice.
4. Synched entity data — a sheep is sheared and every screen in range agrees within the tick. The slot the wool lives in is written nowhere in Sheep: it is 18 because eighteen slots were handed out above it, and the packet stops at 254 because 255 means stop.
5. Attributes — Strength II lands, and no packet is sent at all. Eight of the forty attributes never reach the client, and attack damage is one of them.
6. Movement and collision — one tick of a falling zombie. The mover answers what did I walk through afterwards, by replaying the tick’s movement, which is why fire and water touched in one step always end in the extinguish.
7. AI: goals and brains — a villager’s day, and the same machinery under a zombie that has none of it. Schedules are gone: a villager goes to bed because it asked the world what time it is where it is standing.
8. Pathfinding — the other half of the same lecture. Giving up is machinery: the node being walked towards carries a timeout, and the mob you watch walk into a wall and then wander off is running a scheduled surrender.
9. Damage and death — the part’s closer. An arrow, a dozen owners of one number, and one abstract method. A hit that lands inside the red flash usually does nothing at all, and when it is stronger than the last, only its excess lands — silently.

Reference this part uses

Three of them were written for this part. Attributes — all forty, with defaults, ranges and the syncable flag. Entity data serializers — all 43, in wire-id order. Damage outside LivingEntity — what each of the twenty-one non-living classes does when you hit it. Then packets, registries, game rules, math and primitives and diagram lanes.

The part stops at Avatar, the class 26.2 inserted below Player: everything player-shaped is Part VIII, drawing an entity is Part XI, and the prediction ledger behind the blocks you place is Part X.

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