# Transcience

Top-down twin-stick bullet-hell with a dedicated, server-authoritative backend.
Godot 4.7, GDScript only. One executable is both server and client.

**Starting a new session?** [docs/ROADMAP.md](docs/ROADMAP.md) says what is
built, what is next, and which file implements each feature.
[docs/DECISIONS.md](docs/DECISIONS.md) records what the user has already decided
and why — read it before asking a design question, several answers there are not
the obvious default.

## Commands

```bash
tools/check.sh      # parse-check every script (~5s) -- run after every edit
tools/test.sh       # GUT suite, headless (~3s)
tools/smoke.sh      # real server + 4 bot clients over ENet (~40s)
tools/server.sh     # dedicated server
tools/client.sh --listen            # host and play, no menu
```

Diagnostics. Each runs as a *scene* (they need the `Net` autoload) and exits
non-zero on failure, so they gate like tests:

```bash
godot --headless --path . res://tools/diag_prediction.tscn    # prediction gap; injects clock drift
godot --headless --path . res://tools/diag_progression.tscn   # kill -> xp -> level -> death -> roster
godot --headless --path . res://tools/diag_loot.tscn          # drop -> pick up -> persist -> use -> drop
godot --headless --path . res://tools/diag_upgrades.tscn      # level -> choice -> taken at the NPC -> new stats
godot --headless --path . --script tools/bench.gd             # sim cost per tick
python3 tools/build_local_assets.py                           # rebuild the local-only bullet atlas
```

`diag_progression`, `diag_loot` and `diag_upgrades` exist because the bot smoke
test cannot cover any of them: bots are poor shots, so they rarely kill
anything, which means they neither earn levels, produce drops, nor ever reach
the quartermaster.

Everything after `--` goes to `GameOpts.parse()`:

| Flag | Effect |
| --- | --- |
| `--server` | Dedicated server, no view. |
| `--join` | Skip the menu and connect. |
| `--listen` | Skip the menu and host a listen server with a local player. |
| `--bot` | Scripted input instead of the keyboard. Implies `--join`. |
| `--host`, `--port`, `--name` | Connection details. |
| `--autoquit N` | Quit after N physics ticks. |
| `--boss-rush` | Server-side: dungeons spawn the boss and no trash. |
| `--depth N` | Server-side: depth of new dungeons, which drives map size. |
| `--account N` | Client-side: override the local account, so several clients can coexist on one machine. |
| `--store PATH` | Server-side: character store location. Use a scratch path in tests. |
| `--verbose` / `--quiet` | Log level. |

A change is done when `check.sh`, `test.sh` and — if it touched networking,
instances or the simulation — `smoke.sh` all pass. Say so explicitly; do not
report a networking change as working on the strength of unit tests alone.

## Hooks

`tools/install-hooks.sh` once per clone (points `core.hooksPath` at
`.githooks/`, committed in the repo — plain bash, no `pre-commit` framework, so
cloning costs nothing extra to run tools/*.sh). Own `.gd` files (not vendored
`addons/`) trigger `check.sh` + `test.sh` on commit (~7s); `smoke.sh` runs on
push (~35s, skip deliberately with `SKIP_SMOKE_HOOK=1 git push`).

## The one rule

**The server decides everything; the client only sends intent.**

A client can send exactly two things: an [InputFrame] (move vector, aim angle,
five button bits, an inventory slot) and a handshake — plus the two low-rate
character-roster requests, which are also pure intent. There is no message for
"I moved here", "I hit that", "I took damage", "my escape finished" or "I now
own this item". Adding one would collapse the whole security model, so don't —
validate-after-the-fact is strictly weaker than having no code path at all.

When a new player action needs a message, look at whether it fits in the input
frame first. Item use and drop did, and got the redundancy, the replay guard and
the per-tick rate limit for free. The cost was one rule: anything in the input
frame that must not repeat has to be **edge-triggered** (see `prev_buttons`),
because frames are resent and a starved server coasts on the last one it holds.

`SimWorld.authoritative` is `true` on the server and `false` on the client. In
replica mode the world runs no AI, fires no emitters and resolves no hits; it
only integrates bullets it was told about. `tests/unit/test_server_authority.gd`
and `tests/integration/test_replica_parity.gd` pin this down.

## Layout

| Path | What lives there |
| --- | --- |
| `src/sim/` | The whole game as plain RefCounted objects. No nodes, no physics server, no rendering. |
| `src/actors/` | Data-only `Resource` definitions: `EnemyDef`, `BossDef`, `ItemDef`, `LootDrop`, `DungeonDef`, `UpgradeDef`. Shapes, not instances. |
| `src/sim/patterns/` | Bullet emitters — the authoring surface for every enemy and boss. Emitters are stateless: they are shared resources, and two bosses of the same kind must not stomp each other. |
| `src/sim/map_grid.gd` | Tile grid: collision, line of sight, chunk streaming. |
| `src/sim/map_gen.gd` | Dungeon generation; `build()` is the only entry point. |
| `src/content/rooms.gd` | Hand-authored room stamps (hub, boss arenas) as text. |
| `src/meta/` | Accounts, characters, persistence, XP curve. Server-owned. |
| `src/content/content.gd` | All enemies and bosses, defined in code. Source of truth. |
| `src/content/items.gd` | All items, same idea. `Items.ORDER` is the wire format — append only. |
| `src/content/dungeons.gd` | The kinds of run. `Dungeons.ORDER` is both a wire format and the hub's portal order. |
| `src/content/upgrades.gd` | The seven upgrades and their draw weights. `Upgrades.ORDER` is a wire format. |
| `src/net/` | Codec, `ServerRuntime`, `ClientRuntime`. |
| `src/instances/` | Lobby hub and dungeon runs. |
| `src/view/`, `src/ui/` | Read-only rendering. Never decides anything. |
| `src/autoload/net.gd` | The only autoload. RPC surface. |
| `tools/` | Headless tooling. |

The simulation must not import anything from `src/net/`, `src/view/` or
`src/ui/`, and must not touch `Net`. That is what lets tests drive a thousand
ticks in milliseconds with no SceneTree.

## Godot gotchas that will waste your time

1. **New `class_name` needs a cache refresh.** `.godot/global_script_class_cache.cfg`
   is only rebuilt by the editor or `godot --headless --path . --import`.
   Until then every use of the new class reports `Identifier not declared`,
   which looks like a real error. `check.sh` does the refresh for you.
2. **Autoload names do not resolve under `--script`.** A `--script` run has no
   main loop, so `Net` is `Identifier not found`. Tools that need autoloads must
   run as a scene (see `tools/check.tscn`); tools that don't can use `--script`.
   This is why `GameLog` and `GameOpts` are static classes rather than autoloads.
3. **`ResourceLoader.load()` returns non-null for a broken script.** Never test
   the return value to detect a parse error; read the engine's stderr instead.
   And never call `Script.reload()` on the script you are running — it hangs.
4. **Input events default to `device = 16`, which matches nothing.** Bindings
   must use `device = -1`. `tools/setup_input_map.gd` generates the input map
   correctly; edit that file, not the `[input]` block in `project.godot`.
5. **`set_anchors_preset(preset)` does not zero the offsets.** `keep_offsets`
   defaults to `false`, which despite the name means "recompute offsets to keep
   the control's *current* rect on screen" — for a freshly created Control that
   rect is `(0,0)`-sized, so it comes out pinned to the top-left corner
   regardless of the anchors. Use `set_anchors_and_offsets_preset()` for any
   Control built in code. Separately: `.position` assigns an *absolute*
   coordinate even on an anchored control; `offset_left`/`offset_top` are the
   anchor-relative ones. This combination silently broke the main menu and
   three pieces of the HUD.
6. **`ProjectSettings.save()` drops settings equal to the engine default** and
   strips comments. Anything load-bearing (the 60 Hz tick) is asserted in code
   in `src/main.gd` instead of trusted to `project.godot`.

## Non-obvious invariants

- **`ClientRuntime.process_physics_priority = -10`.** The client must sample and
  send input before `ServerRuntime` ticks, or a listen server's drawn ship sits
  a permanent tick ahead of the authoritative one and bullets trail it. Measure
  with `godot --headless --path . res://tools/diag_prediction.tscn` (~0.1px is
  healthy, 4px means the ordering broke).
- **`PLAYER_RADIUS` (hitbox) < `PLAYER_VISUAL_RADIUS` (sprite), and
  `PLAYER_MUZZLE_OFFSET` derives from the visual one.** Prefer a visible
  near-miss over an invisible hit; keep the muzzle clear of the sprite.
- **`INPUT_MAX_LEAD` must stay well above `INPUT_LEAD_MAX`.** The server's
  input acceptance window has to be wider than the band in which the client
  re-syncs its own numbering. Violate it and drifting clocks land in a silent
  dead zone where the server rejects everything and the client never notices —
  the ship and the authoritative position separate permanently. Pinned by
  `tests/unit/test_input_lead.gd`.
- **Never send the map, or its seed.** Geometry is streamed per peer in chunks
  around that peer's player (`ServerRuntime._stream_map`). The seed would let
  any client regenerate the whole dungeon. `MAP_STREAM_RADIUS` must stay wider
  than `FOG_VIEW_RADIUS`, or prediction runs on terrain the client lacks.
- **Bullet speed must stay under one tile per tick.** Wall collision samples
  position once per tick, so anything faster tunnels. Upgrades multiply bullet
  speed, so `SimConfig.MAX_BULLET_SPEED` clamps the result — without it two
  Snipers put shots through walls. Pinned by
  `test_bullet_speeds_stay_below_the_tunnelling_threshold`.
- **A player's combat numbers are derived, never stored.** `PlayerStats.build()`
  recomputes them from the character's upgrade ids every time, so a saved stat
  cannot disagree with the upgrades that produced it. Upgrade *riders* (split
  charges, poison, erase chance) travel on the bullet instead, because a shot
  in flight must keep what it was fired with.
- **Only `ServerRuntime` writes progression and persistence.** The simulation
  reads a player's level and max health, and moves items between the ground and
  a bag; it never grants experience, retires a character, or touches the store.
  It announces what happened and `ServerRuntime` banks it. One writer means a
  level can never disagree with the experience that earned it, and an inventory
  on disk can never disagree with the one in the world.
- **`Items.ORDER` is a wire format.** An item's index in it is the byte that
  rides the snapshot and every item event. Append, never reorder — reordering
  makes every existing client decode a potion as a ration, so it needs a
  `Protocol.VERSION` bump. `Dungeons.ORDER` is the same, and additionally
  decides which hub portal opens which dungeon (Nth `P` marker in the lobby
  stamp → Nth entry).
- **Which dungeon you enter comes from where you are standing, never from the
  client.** `SimWorld.portal_at()` resolves the player's server-side position
  to a portal, and the `PORTAL_USED` event carries the answer. There is no
  message that names a dungeon, and adding one would let any client pick the
  easy variant's loot rate.
- **Loot has two visibilities, and the instanced one is enforced in the codec.**
  `NetCodec.encode_snapshot` filters items owned by another peer, exactly like
  the actor interest radius. Never move that check into the client: hiding an
  entity the client was handed defends nothing.
- **`LocalAuthProvider` is insecure on purpose.** Any client can claim any
  account. It exists to have the same shape as Steamworks (opaque ticket in,
  64-bit account id out) so swapping is one class. Do not ship it.
- **No contact damage.** Every enemy threatens through bullets only; touching
  one is harmless. `tests/unit/test_content.gd` enforces that every hostile has
  an emitter.
- **A boss never leaves its arena.** `SimWorld._step_boss` clamps to
  `SimBoss.room` *after* movement. Boss rooms deliberately do not lock, so
  walking out is always an escape — which only holds if the boss cannot follow.
- **A telegraph must be visible through fog.** `WorldView._draw_telegraphs`
  ignores line of sight on purpose; everything else in the view respects it. A
  warning you cannot see is an unavoidable hit with extra steps.
- **No i-frames.** Every bullet that touches a player lands; `spawn_grace` is
  the only invulnerable state. Do not reintroduce post-hit immunity — it makes
  dense patterns safer than sparse ones.
- **A disconnect is not an exit.** Dropping in a dungeon keeps the player in the
  world as `linkdead`, channelling out over the same second the escape costs.
  Damage must never cancel the escape channel, or quitting beats the button.
  See [docs/NETCODE.md](docs/NETCODE.md).

## Adding content

A new enemy or boss is data, never code. Add a builder to
`src/content/content.gd` returning an `EnemyDef` / `BossDef` made of the
emitters in `src/sim/patterns/`, register its id in `enemy()` / `boss()` **and
in `ALL_ENEMIES` / `ALL_BOSSES`** (the export tool, the renderer and the tests
all iterate those), and add a test.

A boss phase can move — `BossPhase.Move` is `STATIC`, `ORBIT`, `CHASE` or
`WAYPOINTS`, handled generically in `SimWorld._move_boss`. Movement is a
property of the phase, not of the boss. `tests/unit/test_boss.gd::test_a_brand_new_boss_needs_no_engine_changes`
builds a boss from scratch and asserts the simulation needs no changes to run
it — if you find yourself adding a per-boss branch to `SimWorld`, stop and add
an emitter type instead.

`tools/export_content.gd` writes `.tres` copies into `resources/` for tuning in
the editor inspector. Those are an export, not the source; port changes back.

## Style

Typed GDScript everywhere (`untyped_declaration` is a warning). Tabs, snake_case
files, `PascalCase` class names. Comments explain *why* a thing is the way it is —
the netcode and anti-cheat decisions especially. Keep the existing density.