226 lines
14 KiB
Markdown
Executable File
226 lines
14 KiB
Markdown
Executable File
# Roadmap
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Workspace layout: `shared/` (wire types), `server/` (authoritative sim), `client/` (render
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terminal). The platform layer — window, GPU, input, RGB332 palette — lives in the external
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`pbio` crate (git dependency), not in this repo.
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---
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## Achieved milestones
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- [x] TGA loader: `Image`, `from_tga`, `to_tileset`, `decode_rle` in `client/src/assets.rs`
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- [x] Pixel helpers: `set_pixel`, `extract`, `blit`, `blit_tile` in `client/src/game/pixelhelper.rs`
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— signed `i32` offsets, clip against all four framebuffer edges, index 0 = transparent
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- [x] Input system: `GameAction`, `InputMap`, `InputState` in `client/src/input.rs` (over `pbio::Key`)
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- [x] Protocol spec: `notes/protocol.md` — Header, State, Action, Chunk, Entity, EntityQuery,
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EntityDetail, Ping/Pong; reliability model
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- [x] Shared crate: packet structs as `bytemuck::Pod` with compile-time size assertions,
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`player_action` / `packet_type` constants, `chunk_id` / `chunk_coords`
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- [x] Server binary: 24 Hz tick loop, 3×3-chunk test world (`build_world`), wall collision,
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per-client action queue, `ChunkPacket` dispatch on cache miss, stale-client eviction
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- [x] Client net: `NetClient` in `client/src/net.rs`, non-blocking UDP recv,
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`StatePacket` / `EntityPacket` / `ChunkPacket` / `PongPacket` dispatch, entity-checksum retransmit
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- [x] End-to-end loop: player moves on server, position reflected in `EntityPacket`, rendered on client
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- [x] Tile rendering: chunk-based world rendering from received `ChunkPacket` data (6-bit unpack)
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- [x] Tick-based movement: movement resolved in `entity_tick`, currently every 4th tick (`sim.rs`)
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- [x] Sprite-based entity rendering: entity `type_id` → tile in `entities.tga`, blitted with transparency
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- [x] Phase-staggered broadcast: per-client `send_phase`, flat outbound load across ticks
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- [x] Ping/Pong RTT measurement (`PingPacket` / `PongPacket`)
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- [x] Connection timeout: client emits `Disconnected` after 10 s without a `StatePacket`;
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server evicts clients unseen for 10 s
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- [x] Map loader: Tiled-CSV parser in `server/src/map.rs` (flip-flag masking, content-derived
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dimensions), `load_world` slices it into chunks, invisible solid border at the map rim.
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Replaces the hardcoded `build_world`. See `notes/07-map-loader.md`
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- [x] Client movement prediction: queued unconfirmed steps (`path` in `client/src/game.rs`),
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paced at the server's 6 Hz movement cadence, reconciled against `EntityPacket` positions,
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dropped after idle timeout. Shared collision vocabulary `shared::tile_collidable`
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(currently empty — every tile walkable) keeps client prediction and server sim in lockstep.
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- [x] Click-to-move: framebuffer click → world tile, A* over the chunk cache
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(`client/src/game/pathfind.rs`, unknown chunks count as blocked), route translated into
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cardinal actions one step per movement interval — the server only ever sees movement
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actions and stays authoritative. Keyboard input cancels the route; each step is
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re-validated at send time and a blocked step voids the route. In-flight steps render
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bright blue, planned route dim blue. Click-and-hold steers continuously: while the
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button is held the route keeps replanning toward the tile under the cursor (only
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when that tile changes — cursor or camera movement), sweeping across blocked tiles
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keeps the current route, and a voided route replans automatically while held.
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- [x] 8-directional movement in chessboard geometry: world physics use the Chebyshev
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metric — diagonal and cardinal steps are the same distance, a "circle" is a square
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of tiles, matching the square viewport. Four diagonal actions in
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`shared::player_action`; the single-step rule lives in `shared::step_allowed`
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(king move onto a free tile, diagonals additionally need both orthogonal neighbors
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free — no corner cutting) and is the one function used by the server sim, client
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send-time validation and the client A* (8-connected, Chebyshev heuristic). Two held
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keys walk diagonally.
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- [x] Collision vocabulary seeded with test values (`shared::tile_collidable`): id 146
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(trees/rocks) and id 0 — id 0 doubles as the server's invisible world border, which
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the client previously mispredicted as walkable. A proper tile-data file format
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replaces this table later.
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- [x] Tick-addressed action scheduling (supersedes two interim designs — a sequence-
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deduped FIFO queue and its flow control — that fixed a periodic walking hitch and
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a path/route deadlock but kept two free-running clocks racing each other). Actions
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are now scheduled onto the server's tick timeline: `ActionPacket.target_tick`
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(formerly `sequence`) selects the movement window, a second action to the same
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window *replaces* the first (retraction via NOOP, rescheduling, retransmit dedup),
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late actions fill only an *empty* next window (gap-filling without overriding
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newer intent — needed over real internet links so actions don't die pointlessly),
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and only `ACTION_WINDOW_HORIZON = 3` future windows are addressable. The sim keeps
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per-entity window slot maps and executes at most one action per window, so floods
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can neither grow memory nor speed anyone up. The client estimates the server tick
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from `StatePacket.tick` plus elapsed time and schedules each step into the next
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window — one send per window by construction, no local send timer, no clock-rate
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race. `target_tick = 0` marks keep-alive/cache-ack packets with no scheduling
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intent. See `notes/protocol.md` (ActionPacket).
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- [x] Client-side unexpected-state handling: the movement goal is persistent (outlives
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the planned route) and every surprise reroutes toward it — a blocked route step
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replans instead of voiding the plan, and a confirmed position off the predicted
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path (lost/rejected/overridden step) retracts all still-scheduled steps (NOOP to
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their windows), drops the stale prediction and replans from the confirmed tile.
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Changing plans mid-run (new click/steer target) likewise retracts scheduled-but-
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unexecuted steps, so old intent stops playing out on the server within a window.
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The goal is released on arrival, unreachability, keyboard override, or a discrete
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click on an unreachable tile. This is the "reactive replanning" item formerly
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parked under Later — Robustness.
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- [x] `netsim` — bad-internet simulator (workspace member, dev tool): a UDP proxy adding
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delay, jitter and loss per direction (`--delay/--jitter/--loss`, `--up-*`/`--down-*`
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overrides; reordering emerges from jitter). No root, game-traffic only, zero deps.
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The client takes an optional server address argument to point at it:
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`cargo run -p netsim -- --delay 80 --jitter 30 --loss 5` + `client 127.0.0.1:7778`.
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- [x] Bad-link hardening (netsim immediately broke the naive scheduling — locks under
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isolated loss 15% and isolated delay 120 ms):
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(a) RTT-adaptive scheduling lead — the client pings automatically (1 Hz, smoothed),
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and schedules `ceil((rtt + margin) / window)` windows ahead instead of always one:
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under systematic latency "late" had been the *normal* case. The retraction horizon
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moves out the same way (a cancellation needs the same lead an action does).
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(b) Late-rule cleanup in the sim — a late movement action keeps its *order*, not
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its time (first still-empty upcoming window), so bunched late arrivals no longer
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collapse onto one slot and eat each other; late NOOPs are dropped outright (as
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gap-fillers they used to block real steps: retract → late NOOPs poison upcoming
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windows → replanned steps eaten → retract again — a lock loop).
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(c) Client stall watchdog — steps in flight but nothing confirmed for 750 ms means
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the prediction is dead no matter why (e.g. *all* in-flight actions lost: the server
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never moves, so the moved-off-plan desync detection never fires, path stays full,
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nothing is ever sent again): retract, drop, replan toward the goal.
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`PATH_MAX_LEN` is back to 8 as a pure prediction bound — server safety now comes
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from window addressing, and on a slow link several correct steps are legitimately
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unconfirmed at once (confirmations lag a full RTT).
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- [x] Prediction rebuilt as predict → ack → replay (replaces the per-problem patches
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above with structural robustness; fixed multi-second replan storms at high ping).
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The old model stored absolute predicted tiles and reconciled by tile matching, so
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any surprise "invalidated" the whole prediction and recovery meant clear + replan
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from the confirmed position — but steps inside the retraction horizon cannot be
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cancelled and still execute ("zombies"), shifting the server off every fresh plan
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and re-triggering recovery in a loop. Now: pending steps are `(window, delta)`
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pairs, `EntityPacket.tick` is the acknowledgment cursor (every window ≤ tick/4 is
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provably consumed — executed, rejected or lost, it no longer matters which), and
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the predicted position is always *derived* by replaying pending deltas on top of
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the confirmed position. A surprise shifts the prediction instead of killing it; a
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route that no longer connects triggers one clean replan toward the persistent goal
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via the existing send-time validation. Deleted outright: tile-matching reconcile,
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the moved-off-plan desync heuristic, the stall watchdog, and the idle path drop —
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acked windows expire pending steps automatically, so the path cannot go stale.
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The replay applies each pending delta through the shared `step_allowed` rule —
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exactly as the server will — so a delta the server is going to reject does not
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move the prediction either, and the predicted position can never sit inside a
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wall (previously a diverged prediction could, causing a brief walk-into-wall
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lock until the acks caught up).
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---
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## Upcoming work
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### 06 — Hybrid tick loop *(partially done)*
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Design of record: **`notes/06-hybrid-tick-loop.md`** (24 Hz base tick + stride scheduling).
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This supersedes the original 20/10/1 Hz three-tier sketch.
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- [x] 24 Hz base loop (`server/src/main.rs`)
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- [x] Phase-staggered broadcast at 12 Hz/client (`send_phase` in `server/src/net.rs`)
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- [x] Stride layout settled: `entity_tick` at `%4` (6 Hz, sets movement rate), broadcast at
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`%2` (12 Hz/client). The `06` note now documents this and why.
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- [ ] Action-point model (`energy` / `speed` per entity, act when `energy >= ACTION_COST`).
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Removed from `entity.rs` for now as premature — reintroduce when NPCs (08) actually need it.
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Then `entity_tick` can move to `%2` (12 Hz) and `speed` sets the effective movement rate.
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---
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### 07 — Tiled map loader *(done — see Achieved / `notes/07-map-loader.md`)*
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Remaining follow-ups when the need is concrete:
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- Collision vocabulary: seeded with test values (0, 146) in `shared::tile_collidable`.
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Decide on a proper file format for tile data (collision, opacity, …) instead of a
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hardcoded match, then feed both server and client from it.
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- Tile flipping: orientation is discarded on load; revisit with the sprite pass (09).
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- Multiple / object layers (spawns, triggers) — not yet parsed.
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---
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### 08 — Basic NPC entity + AI budget
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One dumb wandering enemy. Validates the simulation architecture before complexity accumulates.
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Depends on the action-point model from 06 being reintroduced.
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- Add `EntityKind::Npc` with a `think() -> u32` method returning budget cost
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- Per sim-tick: distribute `think_budget = BASE / (clients + 1)` across entities ordered by player proximity
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- Complex entities consume more budget; simple ones less. Loop breaks at zero — natural load shedding.
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- No framework. No trait objects yet. A match on `EntityKind` is fine.
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```rust
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let mut budget: u32 = BASE_BUDGET / (client_count + 1).max(1);
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for entity in entities_by_player_proximity() {
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if budget == 0 { break; }
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budget = budget.saturating_sub(entity.think(&mut world));
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}
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```
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---
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### 09 — Client camera *(camera follow done, entity interpolation open)*
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Sprite rendering already landed (see Achieved). Camera status:
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- [x] Smooth camera follow: the camera is a float pixel position (`cam` in `game.rs`)
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that tracks the player linearly at ~64 px/s, snapping only to whole pixels at
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render time (and outright on teleport-sized corrections). The viewport renders
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with sub-tile offsets (31×31 tile pass + right-strip clip).
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- [x] Entity interpolation: per-id lerp table (`EntityLerp` in `game.rs`) beside the
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entity list — previous/current tile plus a clock, rendered as a pixel lerp over
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one movement interval. Jumps of more than one tile (Chebyshev) snap. Purely
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cosmetic; game logic keeps using authoritative tile positions.
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---
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### Later — UI / HUD
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- Bitmap font renderer: 8×8 glyph sheet TGA, `draw_text(frame, font, x, y, color, text)` — see `notes/04`
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- UI primitives in `client/src/ui.rs`: `fill_rect`, `draw_rect`, `draw_hbar` — see `notes/05`
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- HUD layout (320×240): HP bar + player name bottom 16px, message log right panel
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- A real clip-rect on the blit primitives belongs here — once the viewport and HUD panels are
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two distinct regions, the abstraction earns its keep. Not before.
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---
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### Later — Robustness + auth
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- Auth token handshake: replace source-address identity (`auth_token` field exists but is unused)
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- Per-address rate limiting for the action ingest (only meaningful once identity is real —
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address spoofing bypasses any limit before then)
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- Multi-datagram `EntityPacket`: server currently truncates at 66 entities (`net.rs` TODO)
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- Asset embedding: `include_bytes!` for single-binary distribution
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---
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### Later — World depth
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Once the simulation architecture is stable and a real level exists:
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- Doors, interactive objects (server-authoritative state)
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- Combat: melee range check, HP, death, respawn
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- Inventory: on-demand via `EntityQueryPacket` / `EntityDetailPacket`
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- Day/night and weather on the slow tick — affect visibility, spawns
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- Procedural dungeon generation (BSP or cellular automata feeding into the same tile format)
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---
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</content>
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