Implement main game as a mod

.gitignore

@@ -1,3 +1,4 @@
 build/
 world.json
 world.json.tmp
+server_mods/

MODS.md

@@ -79,7 +79,8 @@ refers to exists (and that it depends on the mods those come from), and typechec
 `common/mod_api/`, which scripts import as `bworld/server`, `bworld/client` and `bworld/worldgen`. Folders in `mods/`
 starting with `_` or `.` are ignored.
 
-The game can't load mods yet; see the [Implementation plan](#implementation-plan).
+`deno task build` builds every mod in `mods/` and fails if any has errors; `deno task server` then loads them. What
+works so far is listed in the [Implementation plan](#implementation-plan).
 
 ## Mod layout
 
@@ -1039,8 +1040,8 @@ Worlds saved before the move must load afterwards with nothing changed:
 
 Each phase ends with every test passing and the game playable.
 
-**Phase 0: safety net.** Do this first, before any other mod work. Started: `deno task test` runs `tests/`, which so far
+**Phase 0: safety net.** Do this first, before any other mod work. Started: `deno task test` runs `tests/`, which covers
-checks `mods/bworld` against the game and the mod tools.
+loading mods (the base game and the template), their scripts and worldgen, saves, and the mod tools.
 
 - Move the test scripts used while building steps 1–3 into the repo as `deno test` files under `tests/`: server logic
   (breaking, placing, crafting, chest, furnace, saves), client and server terrain agreement, click prediction, and the
@@ -1051,13 +1052,13 @@ checks `mods/bworld` against the game and the mod tools.
 - Save a world from the current code with chests, a running furnace and some player inventories as
   `tests/fixtures/world_v2.json`, with a test that loads it and checks everything is where it was.
 
-**Phase 1: data** (after steps 4 and 5).
+**Phase 1: data** (after steps 4 and 5). _Done._
 
 - Create `mods/bworld` with its manifest and credits, and move the 62 textures there. Rename the breaking cracks to
   `engine:break_0`–`8` and the fallback to `engine:missing`.
 - Generate the block, item and recipe JSON with a script that reads the current registries, instead of writing it by
-  hand. Hand-copying 18 blocks' fields is how typos get in. Done: `deno task export-bworld` writes them, and
+  hand. Hand-copying 18 blocks' fields is how typos get in. They were generated this way, checked equal to the
-  `tests/bworld_mod_test.ts` fails if they drift from the game.
+  TypeScript definitions, and those were then deleted.
 - The loader registers the recipes and `server/game/crafting.ts` matches against them. Behaviors stay in
   `server/game/blocks.ts`, still keyed by block id, for now.
 - Delete `common/blocks/` and `common/items/`.
@@ -1106,7 +1107,8 @@ checks `mods/bworld` against the game and the mod tools.
 
 ## Implementation plan
 
-Steps 1–3 are done; the mod steps (4 onwards) aren't started. Each step keeps the game working:
+Steps 1–4 are done and 5, 6 and 9 mostly, enough that a mod made from the template loads and runs. Each step keeps the
+game working:
 
 1. **Game server core.** Move `client/generation.ts` to `common/` (it already only needs constants and the rng package)
    and have the server generate terrain. Move world state, chunks, tile data and player inventories into a game server
@@ -1119,16 +1121,22 @@ Steps 1–3 are done; the mod steps (4 onwards) aren't started. Each step keeps
    reach a server, and show a connection error instead.
 4. **Mod loader and build.** Discover mods, check manifests, sort by dependencies, turn JSON into registry entries,
    build the combined atlas (textures are currently all named `bworld:<file>`), bundle scripts per side, and write
-   hashed output to `build/mods/` and `server_mods/`.
+   hashed output to `build/mods/` and `server_mods/`. _Done._
 5. **Delivery.** Split `welcome` into `welcome` / `ready` / `join`. Clients download, verify and run mods before
-   joining. Add the confirm screen for cross-origin servers and CORS headers on the server.
+   joining. Add the confirm screen for cross-origin servers and CORS headers on the server. _Partly done:_ `welcome`
+   lists the mods and clients download and run them before creating the world, but the server doesn't wait for `ready`
+   (its messages just queue up meanwhile), hashes aren't checked, and there's no confirm screen or CORS yet.
 6. **Server scripts.** Components, events, commands, system, storage and `ctx.recipes`. Move `FURNACE_RECIPES` and
-   `FUEL_VALUES` into the recipe registry.
+   `FUEL_VALUES` into the recipe registry. _Mostly done_ (`server/game/mod_runtime.ts`). Not yet: `on_click` (clients
+   don't report left clicks on blocks), item `on_use` (there's no item use action), `world.get_state` / `set_state`
+   (block states aren't synced or saved), and `Container.on_change`. `ctx.containers`, `ctx.ui` and `ctx.net` throw
+   until steps 7 and 8, and so do the client's `ctx.ui`, `ctx.hud`, `ctx.input` and `ctx.net`.
 7. **GUIs.** Forms, then container screens (rebuild chest and furnace with them), then custom screens, the `Graphics`
    API (built on the existing renderer and debug UI widgets) and the HUD.
 8. **Mod channels** and keybinds.
 9. **Worldgen mods.** Worldgen URLs and mod ores go into the chunk worker `init` message. Workers must finish importing
-   before generating anything.
+   before generating anything. _Done for features and ores._ `register_terrain` throws until phase 3 moves the base
+   terrain out of the engine.
 
 Steps 1–3 are engine work every multiplayer feature needs, with or without mods. Mods could start with data only (step 4
 plus data in step 5) before scripts exist.

build.ts

@@ -1,11 +1,26 @@
 import { copy } from "@std/fs";
 import { createCanvas, loadImage } from "@gfx/canvas-wasm";
+import { ENGINE_TEXTURE_DIR, load_and_check, load_order, LoadedMod } from "./tools/check_mods.ts";
+import type { ModData, ModListing } from "./common/mod_loader.ts";
 
-const BUILD_FOLDER = "build";
+// all overridable so tests can build somewhere else
+const BUILD_FOLDER = Deno.env.get("BUILD_DIR") ?? "build";
+const MODS_FOLDER = Deno.env.get("MODS_DIR") ?? "mods";
+// server scripts go here instead of the served build folder, players never get them
+const SERVER_MODS_FOLDER = Deno.env.get("SERVER_MODS_DIR") ?? "server_mods";
 
-function clear_folder() {
+// what the server reads at startup, see server/main.ts
-	Deno.removeSync(BUILD_FOLDER, { recursive: true });
+export interface ServerModIndex {
-	Deno.mkdirSync(BUILD_FOLDER);
+	mods: { listing: ModListing; server?: string }[];
+}
+
+function clear_folder(folder: string) {
+	try {
+		Deno.removeSync(folder, { recursive: true });
+	} catch (e) {
+		if (!(e instanceof Deno.errors.NotFound)) throw e;
+	}
+	Deno.mkdirSync(folder, { recursive: true });
 }
 
 async function build_fonts() {
@@ -59,14 +74,22 @@ function calculate_atlas_size(count: number) {
 	};
 }
 
-async function build_atlas_from_folder(folder: string) {
+// one atlas with the engine's textures (engine:<file>) and every mod's (<mod>:<file>)
-	let sprite_count = 0;
+async function build_atlas(mods: LoadedMod[]) {
-	for (const entry of Deno.readDirSync(folder)) {
+	const textures = new Map<string, string>();
-		console.assert(entry.isFile && entry.name.endsWith(".png"));
+	for (const entry of Deno.readDirSync(ENGINE_TEXTURE_DIR)) {
-		sprite_count += 1;
+		if (entry.isFile && entry.name.endsWith(".png")) {
+			textures.set(`engine:${entry.name.replace(".png", "")}`, `${ENGINE_TEXTURE_DIR}/${entry.name}`);
+		}
+	}
+	for (const mod of mods) {
+		for (const [id, path] of mod.texture_files) {
+			textures.set(id, path);
+		}
 	}
 
-	const atlas = calculate_atlas_size(sprite_count);
+	// + 1 for the missing texture
+	const atlas = calculate_atlas_size(textures.size + 1);
 
 	const canvas = createCanvas(atlas.size, atlas.size);
 	const ctx = canvas.getContext("2d");
@@ -80,40 +103,119 @@ async function build_atlas_from_folder(folder: string) {
 	ctx.fillStyle = "black";
 	ctx.fillRect(8, 0, 8, 8);
 	ctx.fillRect(0, 8, 8, 8);
+	atlas_info["engine:missing"] = { x: 0, y: 0 };
 
 	let index = 1;
-	for (const entry of Deno.readDirSync(folder)) {
+	for (const [id, path] of [...textures].sort(([a], [b]) => a.localeCompare(b))) {
-		const sprite = await loadImage(`${folder}/${entry.name}`);
+		const sprite = await loadImage(path);
 		const row = Math.floor(index / atlas.sprites_per_side);
 		const column = index % atlas.sprites_per_side;
 		ctx.drawImage(sprite, column * SPRITE_SIZE, row * SPRITE_SIZE);
 		index += 1;
-
-		const id = `bworld:${entry.name.replace(".png", "")}`;
 		atlas_info[id] = { x: column, y: row };
 	}
 
-	Deno.writeFileSync(`${BUILD_FOLDER}/${folder}.png`, canvas.toBuffer());
+	Deno.writeFileSync(`${BUILD_FOLDER}/assets/sprites/textures.png`, canvas.toBuffer());
-	Deno.writeTextFileSync(`${BUILD_FOLDER}/${folder}.json`, JSON.stringify(atlas_info));
+	Deno.writeTextFileSync(`${BUILD_FOLDER}/assets/sprites/textures.json`, JSON.stringify(atlas_info));
 }
 
-async function build_sprites() {
+async function build_sprites(mods: LoadedMod[]) {
 	for (const entry of Deno.readDirSync("assets/sprites")) {
 		if (entry.name.endsWith(".png")) {
 			await copy(`assets/sprites/${entry.name}`, `${BUILD_FOLDER}/assets/sprites/${entry.name}`);
-		} else if (entry.isDirectory) {
-			await build_atlas_from_folder(`assets/sprites/${entry.name}`);
 		}
 	}
+	await build_atlas(mods);
 }
 
-async function build_assets() {
+async function build_assets(mods: LoadedMod[]) {
 	Deno.mkdirSync(`${BUILD_FOLDER}/assets`, { recursive: true });
 	await copy("assets/ASSETS.md", `${BUILD_FOLDER}/assets/ASSETS.md`);
 
-	build_fonts();
+	await build_fonts();
 	Deno.mkdirSync(`${BUILD_FOLDER}/assets/sprites`, { recursive: true });
-	await build_sprites();
+	await build_sprites(mods);
+}
+
+// every mod in mods/, checked and sorted so dependencies load first. a broken mod fails the whole build,
+// the game never runs with some mods missing
+function load_mods(): LoadedMod[] {
+	const mods = load_and_check(MODS_FOLDER);
+	const problems = mods.flatMap((mod) => mod.report.errors.map((error) => `  ${mod.id}: ${error}`));
+	if (problems.length > 0) {
+		throw new Error(`Mods have errors (deno task check-mods for details):\n${problems.join("\n")}`);
+	}
+	return load_order(mods);
+}
+
+async function bundle_script(path: string, platform: "browser" | "deno"): Promise<string> {
+	const result = await Deno.bundle({ entrypoints: [path], platform, write: false, minify: false });
+	if (!result.success || !result.outputFiles?.length) {
+		throw new Error(`Couldn't bundle ${path}:\n${result.errors.map((e) => e.text).join("\n")}`);
+	}
+	return result.outputFiles[0].text();
+}
+
+async function short_hash(parts: string[]) {
+	const digest = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(parts.join("\0")));
+	return [...new Uint8Array(digest)].slice(0, 6).map((b) => b.toString(16).padStart(2, "0")).join("");
+}
+
+// build/mods/<id>/<hash>/ gets what players download, server_mods/ the server scripts
+async function build_mods(mods: LoadedMod[]) {
+	clear_folder(SERVER_MODS_FOLDER);
+	const index: ServerModIndex = { mods: [] };
+
+	for (const mod of mods) {
+		const manifest = mod.manifest as { name: string; version: string; scripts?: Record<string, string> };
+		const scripts = manifest.scripts ?? {};
+
+		const data: ModData = {
+			blocks: mod.blocks.map((b) => b.json),
+			items: mod.items.map((i) => i.json),
+			recipes: mod.recipes.map((r) => r.json),
+			ores: mod.ores.map((o) => o.json),
+		};
+		const data_json = JSON.stringify(data);
+		const client = scripts.client ? await bundle_script(`${mod.dir}/${scripts.client}`, "browser") : undefined;
+		const worldgen = scripts.worldgen
+			? await bundle_script(`${mod.dir}/${scripts.worldgen}`, "browser")
+			: undefined;
+		const server = scripts.server ? await bundle_script(`${mod.dir}/${scripts.server}`, "deno") : undefined;
+
+		const hash = await short_hash([data_json, client ?? "", worldgen ?? ""]);
+		const public_dir = `mods/${mod.id}/${hash}`;
+		Deno.mkdirSync(`${BUILD_FOLDER}/${public_dir}`, { recursive: true });
+
+		const listing: ModListing = {
+			id: mod.id,
+			name: manifest.name,
+			version: manifest.version,
+			hash,
+			data: `${public_dir}/data.json`,
+		};
+		Deno.writeTextFileSync(`${BUILD_FOLDER}/${listing.data}`, data_json);
+		if (client) {
+			listing.client = `${public_dir}/client.js`;
+			Deno.writeTextFileSync(`${BUILD_FOLDER}/${listing.client}`, client);
+		}
+		if (worldgen) {
+			listing.worldgen = `${public_dir}/worldgen.js`;
+			Deno.writeTextFileSync(`${BUILD_FOLDER}/${listing.worldgen}`, worldgen);
+		}
+
+		const entry: ServerModIndex["mods"][number] = { listing };
+		if (server) {
+			const server_dir = `${SERVER_MODS_FOLDER}/${mod.id}/${await short_hash([server])}`;
+			Deno.mkdirSync(server_dir, { recursive: true });
+			entry.server = `${server_dir}/server.js`;
+			Deno.writeTextFileSync(entry.server, server);
+		}
+		index.mods.push(entry);
+	}
+
+	Deno.writeTextFileSync(`${SERVER_MODS_FOLDER}/index.json`, JSON.stringify(index, null, "\t"));
+	console.log(`Mods: ${mods.map((m) => m.id).join(", ") || "none"}`);
 }
 
 async function build_client() {
@@ -130,20 +232,32 @@ async function build_client() {
 async function build() {
 	try {
 		const now = performance.now();
-		clear_folder();
+		clear_folder(BUILD_FOLDER);
-		await build_assets();
+		const mods = load_mods();
+		await build_assets(mods);
 		await build_client();
+		await build_mods(mods);
 		console.log(`Built in ${(performance.now() - now).toFixed(2)}ms`);
 	} catch (e) {
-		console.log(e);
+		// no index means the server refuses to start, instead of running without some mods
+		try {
+			Deno.removeSync(`${SERVER_MODS_FOLDER}/index.json`);
+		} catch { /* wasn't there */ }
+		console.log(e instanceof Error ? e.message : e);
+		return false;
 	}
+	return true;
 }
 
 let last_build = 0;
 
 if (import.meta.main) {
-	await build();
+	const ok = await build();
-	const watcher = Deno.watchFs(["assets", "client", "common"], { recursive: true });
+	// deno task build --once, for scripts and ci
+	if (Deno.args.includes("--once")) {
+		Deno.exit(ok ? 0 : 1);
+	}
+	const watcher = Deno.watchFs(["assets", "client", "common", MODS_FOLDER], { recursive: true });
 	for await (const event of watcher) {
 		const now = performance.now();
 		if (now - last_build < 500) {

client/components/dimension.ts

@@ -6,6 +6,7 @@ import { AIR, CHUNK_AREA, CHUNK_HEIGHT, CHUNK_SIZE, Faces, ID_MASK, VOID } from
 import { AssetManager } from "../assets.ts";
 import { ClientWorld } from "../client_world.ts";
 import { ChunkWorkerPool } from "../chunk_workers.ts";
+import { worldgen_mods } from "../mods.ts";
 import type { FromChunkWorker } from "../workers/chunk_messages.ts";
 import { create_vertex_buffer, destroy_vertex_buffer, Texture } from "../renderer/mod.ts";
 import { Camera } from "./camera.ts";
@@ -69,6 +70,8 @@ export class Dimension extends Component {
 			block_ids,
 			textures_info: AssetManager.instance.get("bworld:textures_info"),
 			image: { width: this.image.width, height: this.image.height },
+			worldgen_scripts: worldgen_mods.scripts,
+			ores: worldgen_mods.ores,
 		});
 	}
 

client/main.ts

@@ -4,9 +4,7 @@ import { InputManager } from "./input_manager.ts";
 import { Connection, get_player_name, get_server_url } from "./network.ts";
 import { begin_drawing, clear_background, end_drawing, init_font, init_window } from "./renderer/mod.ts";
 import { is_stopped, show_fatal_error } from "./fatal.ts";
-
+import { load_client_mods, set_mods_world } from "./mods.ts";
-await import("$/common/blocks/mod.ts");
-await import("$/common/items/mod.ts");
 
 export class ClientLoop {
 	running = false;
@@ -94,16 +92,30 @@ init_font();
 
 // the game only runs against a server, it owns the world and everything in it
 const connection = await Connection.open(get_server_url(), get_player_name());
+let mods_loaded = false;
 if (connection) {
 	console.log(`Connected to ${get_server_url()}`);
+	try {
+		// blocks, items and textures all come from mods, so this happens before anything else
+		await load_client_mods(connection.mods);
+		console.log(`Mods: ${connection.mods.map((mod) => `${mod.id} ${mod.version}`).join(", ") || "none"}`);
+		mods_loaded = true;
+	} catch (e) {
+		console.error(e);
+		show_fatal_error(`Couldn't load the server's mods: ${e instanceof Error ? e.message : e}`);
+		connection.socket.close();
+	}
+}
 
+if (connection && mods_loaded) {
 	const client_world = new ClientWorld(connection);
+	set_mods_world(client_world);
 	client_world.add_chat("Connected to the server");
 
 	const loop = new ClientLoop(client_world);
 	loop.start();
 
 	console.log("Game started");
-} else {
+} else if (!connection) {
 	show_fatal_error(`Couldn't connect to the server at ${get_server_url()}`);
 }

client/mods.ts

@@ -0,0 +1,87 @@
+// loads the mods the server lists: registers their data, then runs their client scripts.
+// see "Delivery to clients" in MODS.md
+import { AIR } from "$/common/constants.ts";
+import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
+import type { ClientContext } from "$/common/mod_api/client.ts";
+import { ModData, ModListing, ModLoadError, register_mod_data } from "$/common/mod_loader.ts";
+import type { OreJson } from "$/common/mod_data.ts";
+import { AIR_ID } from "$/common/protocol.ts";
+import { Position } from "$/common/components/position.ts";
+import type { ClientWorld } from "./client_world.ts";
+
+// what the chunk workers need to generate the same world as the server
+export const worldgen_mods: { scripts: { mod: string; url: string }[]; ores: OreJson[] } = { scripts: [], ores: [] };
+
+// set once the world exists, mods can't look at it during setup
+let world: ClientWorld | undefined;
+
+export function set_mods_world(client_world: ClientWorld) {
+	world = client_world;
+}
+
+export async function load_client_mods(listings: ModListing[]) {
+	const site = new URL("/", location.href);
+
+	const datas = await Promise.all(listings.map(async (listing) => {
+		const response = await fetch(new URL(listing.data, site));
+		if (!response.ok) {
+			throw new ModLoadError(listing.id, `couldn't download its data (${response.status})`);
+		}
+		return { id: listing.id, data: await response.json() as ModData };
+	}));
+	const recipes = register_mod_data(datas);
+
+	worldgen_mods.ores = recipes.ores;
+	worldgen_mods.scripts = listings.flatMap((listing) =>
+		listing.worldgen ? [{ mod: listing.id, url: new URL(listing.worldgen, site).href }] : []
+	);
+
+	for (const listing of listings) {
+		if (!listing.client) continue;
+		const module = await import(new URL(listing.client, site).href);
+		if (typeof module.setup !== "function") {
+			throw new ModLoadError(listing.id, "the client script doesn't export a setup function");
+		}
+		await module.setup(client_context(listing));
+	}
+}
+
+function client_context(listing: ModListing): ClientContext {
+	const mod = listing.id;
+	const not_yet = (name: string, where: string) =>
+		new Proxy({}, {
+			get: (_, prop) => () => {
+				throw new Error(`[${mod}] ctx.${name}.${String(prop)} isn't implemented yet (${where} in MODS.md)`);
+			},
+		});
+	const need_world = () => {
+		if (!world) throw new Error(`[${mod}] the world isn't there yet during setup`);
+		return world;
+	};
+
+	return {
+		mod: { id: mod, version: listing.version },
+		ui: not_yet("ui", "step 7") as ClientContext["ui"],
+		hud: not_yet("hud", "step 7") as ClientContext["hud"],
+		input: not_yet("input", "step 8") as ClientContext["input"],
+		net: not_yet("net", "step 8") as ClientContext["net"],
+		player: {
+			get name() {
+				return need_world().connection.name;
+			},
+			get position() {
+				const [player] = need_world().get_tag("player")!;
+				const position = player.get(Position)!;
+				return { x: position.x, y: position.y, z: position.z };
+			},
+		},
+		world: {
+			get_block(x, y, z) {
+				const nid = need_world().dimension.get_block(x, y, z);
+				if (nid === AIR) return AIR_ID;
+				return EverythingRegistry.get_by_id<BlockRegistry>("blocks", nid)?.id;
+			},
+		},
+		log: (...args) => console.log(`[${mod}]`, ...args),
+	};
+}

client/network.ts

@@ -1,4 +1,5 @@
 import { BlockChange, ClientMessage, PlayerInfo, ServerMessage } from "$/common/protocol.ts";
+import type { ModListing } from "$/common/mod_loader.ts";
 
 const CONNECT_TIMEOUT_MS = 3000;
 
@@ -13,7 +14,9 @@ export interface RemotePlayer extends PlayerInfo {
 export class Connection {
 	socket: WebSocket;
 	id: string;
+	name: string;
 	seed: string;
+	mods: ModListing[];
 	initial_changes: BlockChange[];
 	spawn: { x: number; y: number; z: number; yaw: number; pitch: number };
 	selected_slot: number;
@@ -26,7 +29,9 @@ export class Connection {
 	constructor(socket: WebSocket, welcome: Extract<ServerMessage, { type: "welcome" }>) {
 		this.socket = socket;
 		this.id = welcome.id;
+		this.name = welcome.name;
 		this.seed = welcome.seed;
+		this.mods = welcome.mods;
 		this.initial_changes = welcome.changes;
 		this.spawn = welcome.spawn;
 		this.selected_slot = welcome.selected_slot;

client/systems/network_system.ts

@@ -75,6 +75,13 @@ export class NetworkSystem extends System {
 					}
 					break;
 				}
+				case "teleport": {
+					const position = local_player.get(Position)!;
+					position.x = message.x;
+					position.y = message.y;
+					position.z = message.z;
+					break;
+				}
 				case "close_screen":
 					// closed by the server (the block broke), it already put everything back
 					player_component.screens = player_component.screens.filter((s) => !(s instanceof GuiContainer));

client/systems/rendering/player.ts

@@ -102,7 +102,7 @@ export function render_player_breaking(player_component: PlayerComponent) {
 		if (Number.isNaN(break_sprite)) {
 			return;
 		}
-		const region = get_sprite_region(`bworld:break_${break_sprite}`);
+		const region = get_sprite_region(`engine:break_${break_sprite}`);
 
 		for (const fn of FACE_FUNCTIONS) {
 			fn(

client/systems/rendering/render_utils.ts

@@ -231,7 +231,7 @@ export function draw_item(item: ItemStack, x: number, y: number) {
 
 // ey its not a bad name
 function draw_item_item(item: ItemStack, item_info: ItemRegistry, x: number, y: number) {
-	let texture_id = "bworld:missing";
+	let texture_id = "engine:missing";
 	if (typeof item_info?.texture_id === "string") {
 		texture_id = item_info.texture_id;
 	} else if (typeof item_info?.texture_id === "function") {
@@ -256,9 +256,9 @@ function draw_item_block(_item: ItemStack, item_info: ItemRegistry, x: number, y
 
 	if (!block_info) throw new Error(`no textures for ${item_info.block_id}`);
 
-	let front_texture = "bworld:missing";
+	let front_texture = "engine:missing";
-	let top_texture = "bworld:missing";
+	let top_texture = "engine:missing";
-	let left_texture = "bworld:missing";
+	let left_texture = "engine:missing";
 
 	const textures = block_info.textures;
 

client/workers/chunk_messages.ts

@@ -1,5 +1,6 @@
 import type { BlockRegistry } from "$/common/everything_registry.ts";
 import type { SpriteRegion } from "$/common/constants.ts";
+import type { OreJson } from "$/common/mod_data.ts";
 
 // messages between the main thread and the chunk workers
 
@@ -11,6 +12,9 @@ export type ToChunkWorker =
 		block_ids: Record<string, number>;
 		textures_info: Record<string, SpriteRegion>;
 		image: { width: number; height: number };
+		// mods' worldgen scripts and ores, so generation matches the server
+		worldgen_scripts: { mod: string; url: string }[];
+		ores: OreJson[];
 	}
 	| { type: "generate"; chunk_x: number; chunk_z: number; seed: string }
 	| { type: "mesh"; chunk_x: number; chunk_z: number; version: number; padded_chunk: Uint32Array };

client/workers/chunk_worker.ts

@@ -4,7 +4,8 @@ import type { BlockRegistry } from "$/common/everything_registry.ts";
 import type { SpriteRegion } from "$/common/constants.ts";
 import type { Texture } from "../renderer/types.ts";
 import type { FromChunkWorker, ToChunkWorker } from "./chunk_messages.ts";
-import { generate_raw_chunk } from "$/common/generation.ts";
+import { generate_raw_chunk, WorldgenSetup } from "$/common/generation.ts";
+import { load_worldgen } from "$/common/worldgen_loader.ts";
 
 const pad = 0.5;
 
@@ -266,8 +267,11 @@ let blocks_registry: BlockRegistry[] = [];
 let block_ids: Record<string, number> = {};
 let textures_info: TexturesInfo = {};
 let image: Texture;
+let worldgen: WorldgenSetup | undefined;
+// generating has to wait for mods' worldgen scripts, or this worker's terrain wouldn't match the server's
+let worldgen_ready: Promise<void> = Promise.resolve();
 
-self.onmessage = (event: MessageEvent<ToChunkWorker>) => {
+self.onmessage = async (event: MessageEvent<ToChunkWorker>) => {
 	const message = event.data;
 	switch (message.type) {
 		case "init":
@@ -275,8 +279,12 @@ self.onmessage = (event: MessageEvent<ToChunkWorker>) => {
 			block_ids = message.block_ids;
 			textures_info = message.textures_info;
 			image = message.image as Texture;
+			worldgen_ready = load_worldgen(message.worldgen_scripts, message.ores).then((setup) => {
+				worldgen = setup;
+			});
 			break;
 		case "generate":
+			await worldgen_ready;
 			generate(message.chunk_x, message.chunk_z, message.seed);
 			break;
 		case "mesh": {
@@ -311,7 +319,7 @@ function post(message: FromChunkWorker, transfer: Transferable[]) {
 }
 
 function generate(chunk_x: number, chunk_z: number, seed: string) {
-	const { blocks, spills } = generate_raw_chunk(chunk_x, chunk_z, seed, block_ids);
+	const { blocks, spills } = generate_raw_chunk(chunk_x, chunk_z, seed, block_ids, worldgen);
 	post({ type: "generated", chunk_x, chunk_z, blocks, spills }, [blocks.buffer, spills.buffer]);
 }
 
@@ -353,12 +361,12 @@ function make_chunk_mesh(
 				const block_info = blocks_registry[block_nid];
 
 				const texture_ids = {
-					top: "bworld:missing",
+					top: "engine:missing",
-					bottom: "bworld:missing",
+					bottom: "engine:missing",
-					front: "bworld:missing",
+					front: "engine:missing",
-					back: "bworld:missing",
+					back: "engine:missing",
-					left: "bworld:missing",
+					left: "engine:missing",
-					right: "bworld:missing",
+					right: "engine:missing",
 				};
 
 				const textures = block_info.textures;

common/blocks/chest.ts

@@ -1,16 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-// behavior lives in server/game/blocks.ts
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:chest", {
-	id: "bworld:chest",
-	textures: "bworld:planks",
-	toughness: 8,
-	requires_tool: false,
-	tool_to_break: "axe",
-	drop_table: "bworld:chest",
-	has_collision: false,
-	interactive: true,
-});
-
-register_block_item(block);

common/blocks/coal_ore.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:coal_ore", {
-	id: "bworld:coal_ore",
-	textures: "bworld:stone_coal",
-	has_collision: true,
-	drop_table: "bworld:coal_ore",
-	toughness: 5,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/copper_ore.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:copper_ore", {
-	id: "bworld:copper_ore",
-	textures: "bworld:stone_copper",
-	has_collision: true,
-	drop_table: "bworld:copper_ore",
-	toughness: 5,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/dirt.ts

@@ -1,15 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-// hoeing it is handled in server/game/blocks.ts
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:dirt", {
-	id: "bworld:dirt",
-	textures: "bworld:dirt",
-	has_collision: false,
-	drop_table: "bworld:dirt",
-	toughness: 2,
-	requires_tool: false,
-	tool_to_break: "shovel",
-});
-
-register_block_item(block);

common/blocks/furnace.ts

@@ -1,16 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-// behavior lives in server/game/blocks.ts
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:furnace", {
-	id: "bworld:furnace",
-	textures: { front: "bworld:furnace", side: "bworld:stone" },
-	has_collision: true,
-	drop_table: "bworld:furnace",
-	toughness: 5,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-	interactive: true,
-});
-
-register_block_item(block);

common/blocks/glass.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:glass", {
-	id: "bworld:glass",
-	textures: "bworld:glass",
-	has_collision: true,
-	transparent: true,
-	toughness: 3,
-	requires_tool: false,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/gold_ore.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:gold_ore", {
-	id: "bworld:gold_ore",
-	textures: "bworld:stone_gold",
-	has_collision: true,
-	drop_table: "bworld:gold_ore",
-	toughness: 5,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/grass.ts

@@ -1,12 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-
-// hoeing it is handled in server/game/blocks.ts
-EverythingRegistry.register<BlockRegistry>("blocks", "bworld:grass", {
-	id: "bworld:grass",
-	textures: { top: "bworld:grass_top", bottom: "bworld:dirt", "side": "bworld:grass_side" },
-	has_collision: false,
-	drop_table: "bworld:dirt",
-	toughness: 2,
-	requires_tool: false,
-	tool_to_break: "shovel",
-});

common/blocks/hoed_dirt.ts

@@ -1,18 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-// TODO: watered state
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:hoed_dirt", {
-	id: "bworld:hoed_dirt",
-	textures: { side: "bworld:dirt", top: "bworld:hoed_dirt", bottom: "bworld:dirt" },
-	has_collision: false,
-	drop_table: "bworld:dirt",
-	toughness: 5,
-	requires_tool: false,
-	tool_to_break: "shovel",
-	states: [
-		{ name: "watered", bits: 1, default: 0 },
-	],
-});
-
-register_block_item(block);

common/blocks/iron_ore.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:iron_ore", {
-	id: "bworld:iron_ore",
-	textures: "bworld:stone_iron",
-	has_collision: true,
-	drop_table: "bworld:iron_ore",
-	toughness: 5,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/leaves.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:leaves", {
-	id: "bworld:leaves",
-	textures: "bworld:leaves",
-	has_collision: true,
-	transparent: true,
-	toughness: 3,
-	requires_tool: false,
-	tool_to_break: "hoe",
-});
-
-register_block_item(block);

common/blocks/log.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:log", {
-	id: "bworld:log",
-	textures: { side: "bworld:log_side", top: "bworld:log_top", bottom: "bworld:log_top" },
-	has_collision: true,
-	drop_table: "bworld:log",
-	toughness: 3,
-	requires_tool: false,
-	tool_to_break: "axe",
-});
-
-register_block_item(block);

common/blocks/mod.ts

@@ -1,19 +0,0 @@
-import "./grass.ts";
-import "./dirt.ts";
-import "./crops.ts";
-import "./water.ts";
-import "./chest.ts";
-import "./furnace.ts";
-import "./stone.ts";
-import "./log.ts";
-import "./sand.ts";
-import "./snow.ts";
-import "./glass.ts";
-import "./hoed_dirt.ts";
-import "./leaves.ts";
-import "./coal_ore.ts";
-import "./copper_ore.ts";
-import "./iron_ore.ts";
-import "./tin_ore.ts";
-import "./gold_ore.ts";
-import "./planks.ts";

common/blocks/planks.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:planks", {
-	id: "bworld:planks",
-	textures: "bworld:planks",
-	has_collision: true,
-	drop_table: "bworld:log",
-	toughness: 3,
-	requires_tool: false,
-	tool_to_break: "axe",
-});
-
-register_block_item(block);

common/blocks/sand.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:sand", {
-	id: "bworld:sand",
-	textures: "bworld:sand",
-	has_collision: true,
-	drop_table: "bworld:sand",
-	toughness: 3,
-	requires_tool: false,
-	tool_to_break: "shovel",
-});
-
-register_block_item(block);

common/blocks/snow.ts

@@ -1,13 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:snow", {
-	id: "bworld:snow",
-	textures: "bworld:snow",
-	has_collision: true,
-	toughness: 2,
-	requires_tool: true,
-	tool_to_break: "shovel",
-});
-
-register_block_item(block);

common/blocks/stone.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:stone", {
-	id: "bworld:stone",
-	textures: "bworld:stone",
-	has_collision: true,
-	drop_table: "bworld:stone",
-	toughness: 3,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/tin_ore.ts

@@ -1,14 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { register_block_item } from "$/common/utils.ts";
-
-const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:tin_ore", {
-	id: "bworld:tin_ore",
-	textures: "bworld:stone_tin",
-	has_collision: true,
-	drop_table: "bworld:tin_ore",
-	toughness: 5,
-	requires_tool: true,
-	tool_to_break: "pickaxe",
-});
-
-register_block_item(block);

common/blocks/water.ts

@@ -1,10 +0,0 @@
-import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<BlockRegistry>("blocks", "bworld:water", {
-	id: "bworld:water",
-	textures: "bworld:water",
-	has_collision: false,
-	transparent: true,
-	alpha: 0.8,
-	replaceable: true,
-});

common/everything_registry.ts

@@ -5,6 +5,9 @@ export class EverythingRegistry {
 	static #id_to_value = new Map<string, unknown[]>();
 
 	static register<T>(registry: string, key: string, value: T): T {
+		if (this.#key_to_id.get(registry)?.has(key)) {
+			throw new Error(`${key} is already registered in ${registry}`);
+		}
 		if (!this.#key_to_id.has(registry)) {
 			this.#key_to_id.set(registry, new Map());
 			this.#id_to_value.set(registry, []);
@@ -49,6 +52,12 @@ export class EverythingRegistry {
 		return this.#id_to_value.get(registry) as T[];
 	}
 
+	// forget everything, for tests that load mods more than once
+	static clear() {
+		this.#key_to_id.clear();
+		this.#id_to_value.clear();
+	}
+
 	// [key, value] pairs in registration order
 	static entries<T>(registry: string): [string, T][] {
 		const values = this.#id_to_value.get(registry) ?? [];
@@ -104,6 +113,8 @@ export interface BlockRegistry {
 	interactive?: boolean;
 	// placing a block into it replaces it, like water
 	replaceable?: boolean;
+	// custom components from mods and their params, the server runs them
+	components?: Record<string, unknown>;
 
 	compiled_states?: CompiledStateDefinition[];
 }
@@ -112,6 +123,9 @@ export interface ItemRegistry<T = unknown | undefined> {
 	texture_id: string | ((item: ItemStack<T>) => string);
 	block_id?: string;
 	tool_type?: string;
+	max_stack?: number;
+	lore?: string;
+	components?: Record<string, unknown>;
 
 	on_create?(item: ItemStack<T>): void;
 

common/generation.ts

@@ -1,9 +1,13 @@
 import { Alea, create_noise_2d, create_noise_3d, NoiseFunction2D, NoiseFunction3D } from "@paulaboks/rng";
-import { CHUNK_HEIGHT, CHUNK_SIZE } from "$/common/constants.ts";
+import { AIR, CHUNK_AREA, CHUNK_HEIGHT, CHUNK_SIZE } from "$/common/constants.ts";
+import type { FeatureChunk } from "$/common/mod_api/worldgen.ts";
+import type { OreJson } from "$/common/mod_data.ts";
 
 // generation runs in a worker now, so it only needs somewhere to put blocks
 export interface BlockSink {
 	add_block(block: { x: number; y: number; z: number; id: string }): void;
+	// the surface height and biome of each column, for later passes
+	set_column?(x: number, z: number, height: number, biome: string): void;
 }
 
 type Biome =
@@ -226,6 +230,7 @@ export function generate_chunk(dimension: BlockSink, cx: number, cz: number, see
 			const height = get_terrain_height(base_height, biome, wx, wz, height_noise);
 
 			const surface_block = get_surface_block(biome);
+			dimension.set_column?.(wx, wz, height, `bworld:${biome}`);
 
 			for (let y = 0; y <= height; y++) {
 				let block = "bworld:stone";
@@ -270,6 +275,36 @@ export function generate_chunk(dimension: BlockSink, cx: number, cz: number, see
 	}
 }
 
+// noise the way mods get it: create_noise_2d(new Alea(seed + "_" + name)), the same as the base terrain's
+const mod_noise_2d = new Map<string, NoiseFunction2D>();
+const mod_noise_3d = new Map<string, NoiseFunction3D>();
+
+export function named_noise_2d(seed: string, name: string): NoiseFunction2D {
+	const key = `${seed}_${name}`;
+	let noise = mod_noise_2d.get(key);
+	if (!noise) {
+		noise = create_noise_2d(new Alea(key));
+		mod_noise_2d.set(key, noise);
+	}
+	return noise;
+}
+
+export function named_noise_3d(seed: string, name: string): NoiseFunction3D {
+	const key = `${seed}_${name}`;
+	let noise = mod_noise_3d.get(key);
+	if (!noise) {
+		noise = create_noise_3d(new Alea(key));
+		mod_noise_3d.set(key, noise);
+	}
+	return noise;
+}
+
+// what mods add to generation, see "World generation" in MODS.md
+export interface WorldgenSetup {
+	ores: OreJson[];
+	features: { id: string; generate: (chunk: FeatureChunk) => void }[];
+}
+
 export interface RawChunk {
 	// numeric block ids, only what this chunk generated itself
 	blocks: Uint32Array;
@@ -277,6 +312,9 @@ export interface RawChunk {
 	spills: Int32Array;
 }
 
+// features that threw, so each is only reported once
+const failed_features = new Set<string>();
+
 // generates one chunk on its own. neighbors' spills get merged in by whoever assembles the world:
 // a chunk's own blocks always win and spills only fill air, so the result doesn't depend on load order
 export function generate_raw_chunk(
@@ -284,26 +322,40 @@ export function generate_raw_chunk(
 	chunk_z: number,
 	seed: string,
 	block_ids: Record<string, number>,
+	worldgen?: WorldgenSetup,
 ): RawChunk {
 	const blocks = new Uint32Array(CHUNK_SIZE * CHUNK_SIZE * CHUNK_HEIGHT);
 	const spills: number[] = [];
+	const heights = new Int32Array(CHUNK_AREA);
+	const biomes: string[] = new Array(CHUNK_AREA);
+
+	const set = (x: number, y: number, z: number, nid: number) => {
+		if (y < 0 || y >= CHUNK_HEIGHT) {
+			return;
+		}
+		const block_chunk_x = Math.floor(x / CHUNK_SIZE);
+		const block_chunk_z = Math.floor(z / CHUNK_SIZE);
+		if (block_chunk_x !== chunk_x || block_chunk_z !== chunk_z) {
+			spills.push(x, y, z, nid);
+			return;
+		}
+		const lx = x - chunk_x * CHUNK_SIZE;
+		const lz = z - chunk_z * CHUNK_SIZE;
+		blocks[y * CHUNK_AREA + lz * CHUNK_SIZE + lx] = nid;
+	};
 
 	generate_chunk(
 		{
 			add_block(block) {
 				const nid = block_ids[block.id];
-				if (nid === undefined || block.y < 0 || block.y >= CHUNK_HEIGHT) {
+				if (nid !== undefined) {
-					return;
+					set(block.x, block.y, block.z, nid);
 				}
-				const block_chunk_x = Math.floor(block.x / CHUNK_SIZE);
+			},
-				const block_chunk_z = Math.floor(block.z / CHUNK_SIZE);
+			set_column(x, z, height, biome) {
-				if (block_chunk_x !== chunk_x || block_chunk_z !== chunk_z) {
+				const index = (z - chunk_z * CHUNK_SIZE) * CHUNK_SIZE + (x - chunk_x * CHUNK_SIZE);
-					spills.push(block.x, block.y, block.z, nid);
+				heights[index] = height;
-					return;
+				biomes[index] = biome;
-				}
-				const lx = block.x - chunk_x * CHUNK_SIZE;
-				const lz = block.z - chunk_z * CHUNK_SIZE;
-				blocks[block.y * CHUNK_SIZE * CHUNK_SIZE + lz * CHUNK_SIZE + lx] = nid;
 			},
 		},
 		chunk_x,
@@ -311,5 +363,119 @@ export function generate_raw_chunk(
 		seed,
 	);
 
+	if (worldgen) {
+		generate_ores(blocks, chunk_x, chunk_z, seed, block_ids, worldgen.ores);
+		generate_features(blocks, heights, biomes, set, chunk_x, chunk_z, seed, block_ids, worldgen.features);
+	}
+
 	return { blocks, spills: new Int32Array(spills) };
 }
+
+// each block an ore replaces becomes the first ore whose noise is above its threshold
+function generate_ores(
+	blocks: Uint32Array,
+	chunk_x: number,
+	chunk_z: number,
+	seed: string,
+	block_ids: Record<string, number>,
+	ores: OreJson[],
+) {
+	const usable = ores
+		.map((ore) => ({ ...ore, nid: block_ids[ore.id], replaces_nid: block_ids[ore.replaces] }))
+		.filter((ore) => ore.nid !== undefined && ore.replaces_nid !== undefined);
+	if (usable.length === 0) {
+		return;
+	}
+	const noises = usable.map((ore) => named_noise_3d(seed, ore.id));
+
+	for (let y = 0; y < CHUNK_HEIGHT; y++) {
+		for (let lz = 0; lz < CHUNK_SIZE; lz++) {
+			for (let lx = 0; lx < CHUNK_SIZE; lx++) {
+				const index = y * CHUNK_AREA + lz * CHUNK_SIZE + lx;
+				const current = blocks[index];
+				if (current === AIR) {
+					continue;
+				}
+				for (let i = 0; i < usable.length; i++) {
+					const ore = usable[i];
+					if (current !== ore.replaces_nid || y < ore.min_y || y > ore.max_y) {
+						continue;
+					}
+					const wx = chunk_x * CHUNK_SIZE + lx;
+					const wz = chunk_z * CHUNK_SIZE + lz;
+					if (noises[i](wx * ore.scale, y * ore.scale, wz * ore.scale) > ore.threshold) {
+						blocks[index] = ore.nid;
+						break;
+					}
+				}
+			}
+		}
+	}
+}
+
+function generate_features(
+	blocks: Uint32Array,
+	heights: Int32Array,
+	biomes: string[],
+	set: (x: number, y: number, z: number, nid: number) => void,
+	chunk_x: number,
+	chunk_z: number,
+	seed: string,
+	block_ids: Record<string, number>,
+	features: WorldgenSetup["features"],
+) {
+	const ids_by_nid: string[] = [];
+	for (const [id, nid] of Object.entries(block_ids)) {
+		ids_by_nid[nid] = id;
+	}
+
+	const local = (x: number, z: number, what: string) => {
+		const lx = x - chunk_x * CHUNK_SIZE;
+		const lz = z - chunk_z * CHUNK_SIZE;
+		if (lx < 0 || lx >= CHUNK_SIZE || lz < 0 || lz >= CHUNK_SIZE) {
+			throw new Error(`${what}(${x}, ${z}) is outside chunk ${chunk_x}, ${chunk_z}`);
+		}
+		return lz * CHUNK_SIZE + lx;
+	};
+
+	for (const feature of features) {
+		const chunk: FeatureChunk = {
+			x: chunk_x,
+			z: chunk_z,
+			seed,
+			rng: new Alea(`${seed}_feature_${feature.id}_${chunk_x}_${chunk_z}`),
+			noise_2d: (name) => named_noise_2d(seed, name),
+			noise_3d: (name) => named_noise_3d(seed, name),
+			height_at: (x, z) => heights[local(x, z, "height_at")],
+			biome_at: (x, z) => biomes[local(x, z, "biome_at")],
+			get_block(x, y, z) {
+				if (y < 0 || y >= CHUNK_HEIGHT) {
+					return undefined;
+				}
+				const nid = blocks[y * CHUNK_AREA + local(x, z, "get_block")];
+				return nid === AIR ? "bworld:air" : ids_by_nid[nid];
+			},
+			set_block(x, y, z, id) {
+				const nid = id === "bworld:air" ? AIR : block_ids[id];
+				if (nid === undefined) {
+					throw new Error(`unknown block ${id}`);
+				}
+				const dx = Math.floor(x / CHUNK_SIZE) - chunk_x;
+				const dz = Math.floor(z / CHUNK_SIZE) - chunk_z;
+				if (Math.abs(dx) > 1 || Math.abs(dz) > 1) {
+					throw new Error(`set_block(${x}, ${y}, ${z}) is more than one chunk away`);
+				}
+				set(x, y, z, nid);
+			},
+		};
+		try {
+			feature.generate(chunk);
+		} catch (e) {
+			// every client and the server hit the same error, so skipping it keeps them in agreement
+			if (!failed_features.has(feature.id)) {
+				failed_features.add(feature.id);
+				console.error(`Worldgen feature ${feature.id} failed, skipping it where it throws:`, e);
+			}
+		}
+	}
+}

common/inventory.ts

@@ -13,12 +13,12 @@ export class ItemStack<T = unknown | undefined> {
 	max_amount: number;
 	data?: T;
 
-	constructor(type_id: string | string, amount: number = 1, max_amount: number = 64) {
+	constructor(type_id: string | string, amount: number = 1, max_amount?: number) {
+		const item_info = EverythingRegistry.get<ItemRegistry>("items", type_id);
 		this.type_id = type_id;
 		this.amount = amount;
-		this.max_amount = max_amount;
+		this.max_amount = max_amount ?? item_info?.max_stack ?? 64;
 		this.data = undefined;
-		const item_info = EverythingRegistry.get<ItemRegistry>("items", type_id);
 		if (item_info?.on_create) {
 			item_info.on_create(this);
 		}

common/items/axe.ts

@@ -1,6 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:axe", {
-	texture_id: "bworld:axe",
-	tool_type: "axe",
-});

common/items/coal.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:coal", {
-	texture_id: "bworld:coal",
-});

common/items/copper_ingot.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:copper_ingot", {
-	texture_id: "bworld:copper_ingot",
-});

common/items/gold_ingot.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:gold_ingot", {
-	texture_id: "bworld:gold_ingot",
-});

common/items/hoe.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:hoe", {
-	texture_id: "bworld:hoe",
-});

common/items/iron_ingot.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:iron_ingot", {
-	texture_id: "bworld:iron_ingot",
-});

common/items/mod.ts

@@ -1,11 +0,0 @@
-import "./watering_can.ts";
-import "./axe.ts";
-import "./pickaxe.ts";
-import "./hoe.ts";
-import "./coal.ts";
-import "./tin_ingot.ts";
-import "./iron_ingot.ts";
-import "./copper_ingot.ts";
-import "./gold_ingot.ts";
-import "./stick.ts";
-import "./wood_pickaxe.ts";

common/items/pickaxe.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:pickaxe", {
-	texture_id: "bworld:pickaxe",
-});

common/items/stick.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:stick", {
-	texture_id: "bworld:stick",
-});

common/items/tin_ingot.ts

@@ -1,5 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:tin_ingot", {
-	texture_id: "bworld:tin_ingot",
-});

common/items/watering_can.ts

@@ -1,16 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-export interface WateringCanData {
-	water: number;
-	max_water: number;
-}
-
-EverythingRegistry.register<ItemRegistry<WateringCanData>>("items", "bworld:watering_can", {
-	texture_id: "bworld:watering_can",
-	on_create(item) {
-		item.data = { water: 0, max_water: 32 };
-	},
-	get_lore(item) {
-		return `Water: ${item.data?.water}/${item.data?.max_water}`;
-	},
-});

common/items/wood_pickaxe.ts

@@ -1,6 +0,0 @@
-import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-
-EverythingRegistry.register<ItemRegistry>("items", "bworld:wood_pickaxe", {
-	texture_id: "bworld:wood_pickaxe",
-	tool_type: "pickaxe",
-});

common/mod_data.ts

@@ -1,5 +1,5 @@
 // the json formats from MODS.md, and converting them to and from the engine's registry entries.
-// the mod loader uses the from_json direction, tools/export_bworld_mod.ts the other one
+// the mod loader uses the from_json direction, tests use both to check nothing is lost
 import type { BlockRegistry, BlockStateDefinition, ItemRegistry } from "./everything_registry.ts";
 
 export const FORMAT_VERSION = 1;
@@ -37,6 +37,15 @@ export interface BlockJson {
 	components?: Record<string, unknown>;
 }
 
+export interface OreJson {
+	id: string;
+	replaces: string;
+	min_y: number;
+	max_y: number;
+	scale: number;
+	threshold: number;
+}
+
 export interface ItemJson {
 	id: string;
 	texture: string;
@@ -82,6 +91,7 @@ export function block_to_json(block: BlockRegistry, has_item: boolean): BlockJso
 	if (block.interactive) json.interactive = true;
 	if (block.replaceable) json.replaceable = true;
 	if (block.states) json.states = block.states;
+	if (block.components) json.components = block.components;
 	return json;
 }
 
@@ -102,6 +112,7 @@ export function block_from_json(json: BlockJson): { block: BlockRegistry; has_it
 	if (json.interactive) block.interactive = true;
 	if (json.replaceable) block.replaceable = true;
 	if (json.states) block.states = json.states;
+	if (json.components) block.components = json.components;
 	return { block, has_item: json.item ?? true };
 }
 
@@ -114,6 +125,9 @@ export function item_to_json(id: string, item: ItemRegistry): ItemJson {
 	const json: ItemJson = { id, texture: item.texture_id };
 	if (item.tool_type !== undefined) json.tool = item.tool_type;
 	if (item.block_id !== undefined) json.places = item.block_id;
+	if (item.max_stack !== undefined) json.max_stack = item.max_stack;
+	if (item.lore !== undefined) json.lore = item.lore;
+	if (item.components) json.components = item.components;
 	return json;
 }
 
@@ -121,6 +135,9 @@ export function item_from_json(json: ItemJson): ItemRegistry {
 	const item: ItemRegistry = { texture_id: json.texture };
 	if (json.tool !== undefined) item.tool_type = json.tool;
 	if (json.places !== undefined) item.block_id = json.places;
+	if (json.max_stack !== undefined) item.max_stack = json.max_stack;
+	if (json.lore !== undefined) item.lore = json.lore;
+	if (json.components) item.components = json.components;
 	return item;
 }
 
@@ -303,6 +320,18 @@ export function validate_recipe(json: unknown): Problems {
 	return problems;
 }
 
+export function validate_ore(json: unknown): Problems {
+	if (!is_object(json)) return ["ore must be an object"];
+	const problems = [...validate_id(json.id, "id"), ...validate_id(json.replaces, "replaces")];
+	for (const key of ["min_y", "max_y", "scale", "threshold"]) {
+		if (typeof json[key] !== "number") problems.push(`${key} must be a number`);
+	}
+	if (typeof json.min_y === "number" && typeof json.max_y === "number" && json.min_y > json.max_y) {
+		problems.push("min_y must not be above max_y");
+	}
+	return problems;
+}
+
 function validate_id(value: unknown, field: string): Problems {
 	return typeof value === "string" && ID_PATTERN.test(value) ? [] : [`${field} must be an id like "my_mod:thing"`];
 }

common/mod_loader.ts

@@ -0,0 +1,89 @@
+// registers mods' data, the same way on the server and on clients
+import { BlockRegistry, EverythingRegistry, ItemRegistry } from "./everything_registry.ts";
+import {
+	block_from_json,
+	BlockJson,
+	grid_recipe_from_json,
+	GridRecipe,
+	item_from_json,
+	ItemJson,
+	OreJson,
+	RecipeJson,
+} from "./mod_data.ts";
+import { register_block_item } from "./utils.ts";
+
+// everything a mod's json files hold, merged into one file by the build (build/mods/<id>/<hash>/data.json)
+export interface ModData {
+	blocks: BlockJson[];
+	items: ItemJson[];
+	recipes: RecipeJson[];
+	ores: OreJson[];
+}
+
+// a mod as the server lists it to clients, in load order. paths are relative to the site root
+export interface ModListing {
+	id: string;
+	name: string;
+	version: string;
+	hash: string;
+	data: string;
+	client?: string;
+	worldgen?: string;
+}
+
+export class RecipeBook {
+	shaped: GridRecipe[] = [];
+	furnace = new Map<string, { output: { id: string; count: number }; cook_time: number }>();
+	fuel = new Map<string, number>();
+	ores: OreJson[] = [];
+}
+
+export class ModLoadError extends Error {
+	constructor(mod: string, message: string) {
+		super(`${mod}: ${message}`);
+		this.name = "ModLoadError";
+	}
+}
+
+// registers every mod's blocks, items and recipes, in the order given (dependencies first)
+export function register_mod_data(mods: { id: string; data: ModData }[]): RecipeBook {
+	const recipes = new RecipeBook();
+
+	for (const { id, data } of mods) {
+		const fail = (message: string): never => {
+			throw new ModLoadError(id, message);
+		};
+		try {
+			for (const json of data.blocks) {
+				const { block, has_item } = block_from_json(json);
+				EverythingRegistry.register<BlockRegistry>("blocks", block.id, block);
+				if (has_item) {
+					register_block_item(block);
+				}
+			}
+			for (const json of data.items) {
+				EverythingRegistry.register<ItemRegistry>("items", json.id, item_from_json(json));
+			}
+		} catch (e) {
+			fail((e as Error).message);
+		}
+
+		for (const recipe of data.recipes) {
+			switch (recipe.type) {
+				case "shaped":
+					recipes.shaped.push(grid_recipe_from_json(recipe));
+					break;
+				case "furnace":
+					if (recipes.furnace.has(recipe.input)) fail(`two furnace recipes for ${recipe.input}`);
+					recipes.furnace.set(recipe.input, { output: recipe.output, cook_time: recipe.cook_time });
+					break;
+				case "fuel":
+					recipes.fuel.set(recipe.item, recipe.burn_time);
+					break;
+			}
+		}
+		recipes.ores.push(...data.ores);
+	}
+
+	return recipes;
+}

common/protocol.ts

@@ -1,6 +1,7 @@
 // messages sent between the client and the server, as json over a websocket
 import type { Faces } from "./constants.ts";
 import type { ItemData } from "./inventory.ts";
+import type { ModListing } from "./mod_loader.ts";
 
 export const AIR_ID = "bworld:air";
 
@@ -58,7 +59,11 @@ export type ServerMessage =
 	| {
 		type: "welcome";
 		id: string;
+		// the server may change the name asked for, like alice to alice2
+		name: string;
 		seed: string;
+		// in load order, the client loads them before joining the world
+		mods: ModListing[];
 		players: PlayerInfo[];
 		changes: BlockChange[];
 		spawn: { x: number; y: number; z: number; yaw: number; pitch: number };
@@ -70,6 +75,7 @@ export type ServerMessage =
 	// also sent to the player who caused it, which corrects anything their client predicted wrong
 	| { type: "set_block"; x: number; y: number; z: number; id: string }
 	| { type: "chat"; from?: string; text: string }
+	| { type: "teleport"; x: number; y: number; z: number }
 	| { type: "container"; container: ContainerKey; items: (ItemData | null)[] }
 	| { type: "cursor"; item: ItemData | null }
 	| { type: "open_screen"; layout: ScreenLayout; properties: Record<string, number> }

common/utils.ts

@@ -39,7 +39,7 @@ export function distance_point_point(ax: number, ay: number, az: number, bx: num
 
 export function register_block_item(block: BlockRegistry) {
 	// TODO: handle block textures
-	let texture_id = "bworld:missing";
+	let texture_id = "engine:missing";
 	if (typeof block.textures === "string") {
 		texture_id = block.textures;
 	}

common/worldgen_loader.ts

@@ -0,0 +1,37 @@
+// imports mods' worldgen scripts and collects what they register. used by client chunk workers and the game server
+import type { WorldgenContext } from "$/common/mod_api/worldgen.ts";
+import type { OreJson } from "$/common/mod_data.ts";
+import type { WorldgenSetup } from "./generation.ts";
+import { ModLoadError } from "./mod_loader.ts";
+
+export async function load_worldgen(scripts: { mod: string; url: string }[], ores: OreJson[]): Promise<WorldgenSetup> {
+	const setup: WorldgenSetup = { ores, features: [] };
+
+	for (const { mod, url } of scripts) {
+		const ctx: WorldgenContext = {
+			register_feature(id, generate) {
+				if (!id.startsWith(`${mod}:`)) {
+					throw new ModLoadError(mod, `feature ${id} must be in the namespace "${mod}"`);
+				}
+				if (setup.features.some((f) => f.id === id)) {
+					throw new ModLoadError(mod, `feature ${id} is registered twice`);
+				}
+				setup.features.push({ id, generate });
+			},
+			register_terrain(id) {
+				throw new ModLoadError(
+					mod,
+					`can't register terrain ${id}: the base terrain is still built into the engine (phase 3 in MODS.md)`,
+				);
+			},
+		};
+
+		const module = await import(url);
+		if (typeof module.setup !== "function") {
+			throw new ModLoadError(mod, "the worldgen script doesn't export a setup function");
+		}
+		await module.setup(ctx);
+	}
+
+	return setup;
+}

deno.json

@@ -5,7 +5,6 @@
 		"server": "deno run --unstable-worker-options --allow-net --allow-read --allow-write --allow-env server/main.ts",
 		"new-mod": "deno run --allow-read --allow-write tools/new_mod.ts",
 		"check-mods": "deno run --allow-read --allow-run tools/check_mods.ts",
-		"export-bworld": "deno run --allow-read --allow-write --allow-run tools/export_bworld_mod.ts",
 		"test": "deno test --allow-read --allow-write --allow-run tests/"
 	},
 	"compilerOptions": {
@@ -28,6 +27,7 @@
 		"@std/assert": "jsr:@std/assert@^1.0.0",
 		"@std/fs": "jsr:@std/fs@^1.0.23",
 		"@std/http": "jsr:@std/http@^1.0.23",
+		"@std/path": "jsr:@std/path@^1.0.0",
 		"gl-matrix": "npm:gl-matrix@^3.4.4",
 		"marked": "npm:marked@^17.0.3"
 	}

deno.lock

@@ -17,6 +17,7 @@
     "jsr:@std/internal@^1.0.12": "1.0.12",
     "jsr:@std/media-types@^1.1.0": "1.1.0",
     "jsr:@std/net@^1.0.6": "1.0.6",
+    "jsr:@std/path@1": "1.1.4",
     "jsr:@std/path@^1.1.4": "1.1.4",
     "jsr:@std/streams@^1.0.17": "1.1.2",
     "npm:gl-matrix@^3.4.4": "3.4.4",
@@ -54,7 +55,7 @@
       "integrity": "3ecbae4ce4fee03b180fa710caff36bb5adb66631c46a6460aaad49515565a37",
       "dependencies": [
         "jsr:@std/internal@^1.0.12",
-        "jsr:@std/path"
+        "jsr:@std/path@^1.1.4"
       ]
     },
     "@std/html@1.0.5": {
@@ -70,7 +71,7 @@
         "jsr:@std/html",
         "jsr:@std/media-types",
         "jsr:@std/net",
-        "jsr:@std/path",
+        "jsr:@std/path@^1.1.4",
         "jsr:@std/streams"
       ]
     },
@@ -102,6 +103,10 @@
       "bin": true
     }
   },
+  "remote": {
+    "http://localhost:8768/mods/copper_tools/33af7e7e9e94/client.js": "2f5008856e1e7b13d0fe658aefcdea38dea80b4805e41101c5ff6c2d3d258245",
+    "http://localhost:8768/mods/copper_tools/33af7e7e9e94/worldgen.js": "a3da997bdfee885433de282338bdba388825868f122c9a8759b2f1bd67120c78"
+  },
   "workspace": {
     "dependencies": [
       "jsr:@gfx/canvas-wasm@~0.4.2",
@@ -109,6 +114,7 @@
       "jsr:@std/assert@1",
       "jsr:@std/fs@^1.0.23",
       "jsr:@std/http@^1.0.23",
+      "jsr:@std/path@1",
       "npm:gl-matrix@^3.4.4",
       "npm:marked@^17.0.3"
     ]

mods/bworld/README.md

@@ -1,21 +1,13 @@
 # bworld
 
-The base game as a mod, following "The base game as a mod" in `MODS.md`.
+The base game as a mod, following "The base game as a mod" in `MODS.md`. The game loads its blocks, items, recipes and
+textures from here, the same way it loads any other mod.
 
-**The game doesn't load this yet.** Until the mod loader exists, the game still registers everything from
+Still built into the engine, by phase:
-`common/blocks/`, `common/items/`, `server/game/crafting.ts` and `server/game/blocks.ts`. The `blocks/`, `items/` and
-`recipes/` folders here are generated from those by:
-
-```sh
-deno task export-bworld
-```
-
-Run it after changing any of them. `tests/bworld_mod_test.ts` fails when this folder and the game disagree.
-
-Still to move here, by phase:
 
 | Phase | What                                                                                                                                                                                                                 |
-| ----- | --------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| ----- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| 1     | Textures from `assets/sprites/textures/` (the build still reads them from there).                                                                               |
+| 2     | Block behavior in `server/game/blocks.ts` (hoeing, chest, furnace) and the watering can's starting water. They become the `bworld:hoeable`, `bworld:storage`, `bworld:furnace` and `bworld:watering_can` components. |
-| 2     | Block behavior from `server/game/blocks.ts`: `bworld:hoeable`, `bworld:storage`, `bworld:furnace`, and the watering can's `bworld:watering_can` item component. |
+| 3     | Terrain, biomes, trees and ores in `common/generation.ts`.                                                                                                                                                           |
-| 3     | Terrain, biomes, trees and ores from `common/generation.ts`.                                                                                                    |
+
+`bworld:stick` has no texture yet, so sticks show as missing.

mods/bworld/blocks/planks.json

@@ -7,6 +7,6 @@
 			"toughness": 3,
 			"tool": "axe"
 		},
-		"drops": "bworld:log"
+		"drops": "bworld:planks"
 	}
 }