kiln/ARCHITECTURE.md

# viberogue — Architecture & Design Notes

## What this is

viberogue is a **game-making system**, not just a game. The model is ZZT (1991, Epic MegaGames) — a DOS game that shipped with a built-in editor and a simple scripting language (ZZT-OOP), which let players create and share their own worlds. The goal here is something similar: a runtime + authoring environment where game worlds are defined in plain text files with embedded scripts, and the engine interprets them.

This document records the architectural decisions made so far and the reasoning behind them, so future development sessions don't have to rediscover the "why."

---

## Tech stack

| Concern | Choice | Reason |
|---------|--------|--------|
| GUI/windowing | eframe 0.33 / egui 0.33 | Pure Rust, retained-mode, works on desktop and (eventually) WASM |
| Scripting | Rhai 1.x | Pure Rust, sandboxed, WASM-compatible; designed for embedding |
| Map format | TOML + serde | Human-readable, good Rust tooling, standard in the ecosystem |

**WASM compatibility is a first-class requirement.** Everything in the stack must compile to WASM. This ruled out Lua (C FFI via mlua/rlua) for scripting. Rhai was chosen specifically because it is pure Rust with no C dependencies and explicit no_std/WASM support.

---

## Module structure

```
src/
  main.rs       — app entry point, rendering, input
  game.rs       — core data types and game logic
  map_file.rs   — TOML deserialization, Board loader
maps/
  start.toml    — the starting map (loaded at launch)
```

### `game.rs` — core types

The types here are the runtime representation of a game world. They are deliberately free of any file-loading or rendering concerns.

**`Glyph`** (`Copy`)  
The visual representation of one cell: a character, a foreground color, and a background color. Stored *per cell* (not per element type) so individual cells can animate or vary their appearance independently — e.g. a "fire" element where each flame tile has a slightly different color — without changing their behavior.

**`Behavior`**  
A plain data struct of runtime behavioral properties — currently `passable: bool` and `opaque: bool`. Returned by `Archetype::behavior()`. Adding a new property (e.g. `shootable`) requires only a new field here; no match arms needed at call sites. This is a deliberate improvement over storing behavior as a bag of booleans on a per-cell or per-archetype basis.

**`Archetype`**  
An enum of named element types: `Empty`, `Wall`, `Object`, `ErrorBlock`. Each variant knows:
- Its canonical map-file name (e.g. `"wall"`) via `name()`
- Its default `Behavior` via `behavior()`
- Its default `Glyph` via `default_glyph()` — used by the editor when stamping a cell

`ErrorBlock` is a sentinel for map files that reference an unknown archetype name. It renders as a yellow `?` on red so malformed maps are immediately visible in-game. It is excluded from `ALL_ARCHETYPES` (the editor's list) because it is not a valid authoring choice.

**Why `Behavior` and `Archetype` are separate types:**  
`Archetype` is the *named class* of a thing — it lets you say "this is a wall" in a map file and in the editor. `Behavior` is the *runtime properties* that drive simulation. Keeping them separate means adding a new property (e.g. `pushable`) only requires a new field on `Behavior`; no match arms need to be updated across the codebase.

**Why Glyph and Archetype are separate:**  
In ZZT, each board tile had both a visual (character + color pair) and an element type. The visual could vary per-tile even for the same element type. We replicate this: `Glyph` is the visual (per-cell), `Archetype` is the class (shared across cells of the same type). This lets you have a wall that's gray in one room and blue in another without creating two archetype variants.

**`Board`**  
The complete unit of a game world — one "room" or "screen" in ZZT terminology. Holds:
- `cells: Vec<(Glyph, Archetype)>` — row-major grid; each cell directly owns its visual and behavioral class
- `player: Player` — current player position on this board
- `objects: Vec<ObjectDef>` — scripted objects (parsed, not yet runtime-wired)
- `portals: Vec<PortalDef>` — exits to other boards (parsed, not yet runtime-wired)

**Why `cells` is `Vec<(Glyph, Archetype)>` with no palette:**  
An earlier design had `cells: Vec<(Glyph, usize)>` where the `usize` indexed a per-board `elements: Vec<Element>` palette. This was eliminated because the palette indirection added complexity without benefit: `Archetype` is a `Copy` enum (4 bytes), so storing it per-cell is as efficient as storing an index, and it removes the invariant that the index must stay in sync with a specific board's palette.

**Why `Board` is the complete unit (no wrapper struct):**  
An earlier design had `GameMap { board: Board, player: Player, ... }`. This was eliminated because the split was artificial: there's no meaningful use of a `Board` without a player position, and no meaningful use of a player without a `Board`. ZZT itself treats a board as containing everything — the grid, the objects, and the player entry point. Collapsing to a single struct matches the domain model.

**`GameState`**  
Currently a thin wrapper around `Board` that provides game-logic methods (`try_move`). It exists to keep mutation logic (collision checking, movement) separate from the data. As the game grows, event processing and scripting dispatch will live here.

---

### `map_file.rs` — file loading

**`MapFile`** and supporting structs are serde deserialization types only — they exist solely to parse TOML and are never used at runtime.

**`impl From<MapFile> for Board`** — the single conversion point. Reads the palette (each entry maps a character to a `(Glyph, Archetype)` pair), then walks the grid string character-by-character to build `cells`. Unknown archetype names produce an `ErrorBlock` cell and log a warning. This is the only place that knows about both the file format and the runtime representation.

**`pub fn load(path: &str) -> Result<Board, ...>`** — reads a file, deserializes, converts. Called from `main()` before the window is created.

**Why loading happens before window creation:**  
The window minimum size is derived from `board.width` and `board.height`. eframe requires `NativeOptions` (including window size) to be set before calling `run_native`. So the board must be loaded first.

---

### `main.rs` — app + rendering

`App` holds a `GameState`, an `AppMode` (`Play` | `Edit`), and an `EditorState` (`selected: Archetype`). The `update` method:

1. Reads arrow key input and calls `GameState::try_move` — **Play mode only**
2. Draws the menu bar with a File menu and a Play/Edit mode toggle
3. In Edit mode: draws a right-side palette panel listing `ALL_ARCHETYPES` as selectable rows — declared before `CentralPanel` so egui allocates its space first
4. Draws the board: for each cell, a filled background rect then a centered monospace character
5. Draws the player on top using `Glyph::player()` (hardcoded `@` in cyan — the player is not a board cell)
6. In Edit mode: allocates the full viewport as a click target; on click, converts pixel position to cell coordinates and stamps the cell with `(selected.default_glyph(), selected)`

**Cell rendering constants:** `CELL_W = 14.0`, `CELL_H = 20.0` pixels. The board is centered in the CentralPanel when the window is larger than the minimum size. Window min-size is computed for Play mode; the Edit mode palette panel (`PALETTE_PANEL_W = 120.0` px) may clip the board at minimum size.

**Click-to-cell math:** `rel = click_pos - origin; cell_x = (rel.x / CELL_W).floor() as i32`. Negative `rel` values stay negative and are caught by a `>= 0` guard. This mirrors the rendering math exactly so clicks land on the correct cell.

---

## Map file format

XPM-inspired (XPM is an old X11 image format that uses a character palette to define pixel colors). A `[palette]` section maps single characters to both a `Glyph` (visual) and an `Element` (behavior). The `[grid] content` is a TOML multi-line string where each character is a palette key.

```toml
[map]
name = "Room Name"
width = 60
height = 25
player_start = [30, 12]

[palette]
" " = { archetype = "empty", ch = " ", fg = "#000000", bg = "#000000" }
"#" = { archetype = "wall",  ch = "#", fg = "#808080", bg = "#606060" }

[grid]
content = """
############################################################
#                                                          #
############################################################
"""

[[objects]]
x = 10
y = 5
script = """
  on_touch(|| { send_message("open"); });
"""

[[portals]]
x = 59
y = 12
target_map = "cave"
target_entry = "west_door"
```

**Why TOML over a custom format:**  
The `toml` crate gives us deserialization with minimal code. Multi-line strings for the grid give a visual representation of the map. Embedded Rhai scripts fit naturally in TOML multi-line strings without escaping issues.

**Why archetypes by name, not by property:**  
Palette entries used to store `passable = true/false` directly. Switching to `archetype = "wall"` means adding a new behavioral property (e.g. `opaque`) only requires a code change — existing map files don't need to be updated. It also makes files more readable: `archetype = "wall"` is self-documenting. Unknown names produce a visible `ErrorBlock` cell rather than silently defaulting.

**Why the palette approach:**  
A direct mapping from palette character → `(Glyph, Archetype)` means the map file is both human-readable (you can see the shape of the room from the grid string) and flexible (per-cell visual variation is possible by using different palette chars with the same archetype but different colors).

**Colors** are `"#RRGGBB"` hex strings — universally understood, hand-editable.

**`player_start`** is a header field, not a palette character. The player is not a board cell; they are an entity that moves over the board. Using a palette character for player start (like `@` in many roguelikes) would mean the tile under the player is always that character, which makes it awkward to place a player over different terrain.

---

## What's not yet implemented

**Object scripting** — `ObjectDef` and `PortalDef` are parsed from map files and stored on `Board`, but they have no runtime effect yet. The next step here is:
1. Wire `ObjectDef` scripts to Rhai: when the player moves to an object's cell, fire its `on_touch` handler
2. Define the Rhai API surface (what functions scripts can call: `send_message`, movement, board queries)

**Object behavior from scripts** — `Archetype::Object.behavior()` currently returns a static default (`passable: false, opaque: false`). Eventually, `Board::is_passable` will need a special branch for Object cells that reads the behavior from the cell's Rhai script instead.

**Portal navigation** — `PortalDef` stores a `target_map` and `target_entry` but there's no multi-board loading or board switching yet.

**Multi-board world** — right now the engine loads a single `maps/start.toml`. Future: a world file or directory of boards, lazy-loaded as the player moves through portals.

**Editor glyph chooser** — the editor can paint cells with archetypes (default glyphs), but there's no way yet to choose a custom character or color for a cell. The next editor feature is buttons that open char/color picker dialogs.

**File open dialog** — the editor has no way to load a different map file from the UI. This requires a native file dialog (e.g. `rfd`). WASM support for file dialogs is an open question.

---

## Future considerations

These are not current requirements but intended future directions. Where a planned change conflicts with current design, the tension is called out explicitly so it can be addressed before it becomes a problem.

### The player may become an object; boards may have no player

The long-term goal is for the "player" to be an object on the board that happens to respond to arrow key events — not a hardcoded special entity. Some boards may have no player-like object at all and do something else with input events (a cutscene, a menu, a puzzle that reacts to keys differently).

ZZT hard-coded the player as a special element and many game authors had to work around this limitation (e.g. hiding the real player behind a wall and scripting a fake one). This is a deliberate improvement over that model.

**Current design tension:**

The following assumptions are baked in today and will need to change when this is implemented:

- `Board.player: Player` is a required non-optional field. A board with no player can't be represented. This should eventually become `Option<Player>`, or the player should be removed from `Board` entirely and tracked by the engine layer only when present.

- `player_start` in the map file is a required header field. It will need to become optional, or player spawning will move into the object/script system (an object with a special role, spawned at its `x`/`y` position).

- `GameState::try_move` directly mutates `board.player`. Once the player is an object driven by Rhai, movement will go through the scripting dispatch layer instead. `try_move` will likely be replaced by something like `engine.dispatch_event(ArrowKey(dx, dy))`.

- In `main.rs`, the player is rendered as a hardcoded overlay using `Glyph::player()`. Once the player is an object, it should be rendered as part of the normal object layer, not as a special case.

None of these are blockers for current work, but avoid making `Board.player` more central than it already is (e.g. don't add methods that assume player presence, don't derive window sizing from player position).

---

## ZZT reference

ZZT (1991) was a text-mode game for DOS. Its playfield was 60×25 characters (the right 20 columns were the stats panel). Each board was a self-contained screen with objects (tiles with embedded ZZT-OOP scripts), passageways to adjacent boards, and a fixed element type system (about 50 built-in element types). Players could create worlds with the built-in editor and share `.ZZT` files.

viberogue takes the core ideas — tile-based boards, embedded scripts per object, named portals between boards — and rebuilds them in a modern, WASM-capable stack with a more flexible scripting language and a human-readable file format.