Seed the RNG in simInit and load a city once

apps/micropolis/src/lib/cityLoadDeterminism.test.ts

@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+import { loadMicropolisMainModule } from './wasm/node';
+import { createNoopJsCallback } from './wasm/callbacks';
+import { createMapMopViews } from './wasm/views';
+import type { MainModule, Micropolis } from '../types/micropolisengine.d.js';
+
+const CITY = '/cities/kobe.cty';
+
+const loadWithSeed = (engine: MainModule, seed: number): Micropolis => {
+	const micropolis = new engine.Micropolis();
+	micropolis.setCallback(createNoopJsCallback(engine), {});
+	micropolis.init();
+	micropolis.seedRandom(seed);
+	expect(micropolis.loadCity(CITY)).toBe(true);
+	return micropolis;
+};
+
+const mapHash = (engine: MainModule, micropolis: Micropolis): number => {
+	let hash = 0;
+	for (const tile of createMapMopViews(engine, micropolis)!.mapData) hash = (Math.imul(hash, 31) + tile) | 0;
+	return hash >>> 0;
+};
+
+describe('city load determinism', () => {
+	it('same seed gives the same map, a different seed gives another', async () => {
+		const engine = await loadMicropolisMainModule();
+		const first = loadWithSeed(engine, 42);
+		const second = loadWithSeed(engine, 42);
+		const other = loadWithSeed(engine, 7);
+
+		expect(mapHash(engine, second)).toBe(mapHash(engine, first));
+		expect(mapHash(engine, other)).not.toBe(mapHash(engine, first));
+
+		for (const micropolis of [first, second, other]) micropolis.delete();
+	});
+});

packages/micropolis-engine/src/fileio.cpp

@@ -592,8 +592,6 @@ bool Micropolis::loadCity(const std::string &filename)
         std::string newCityName = cityFileName.substr(pos, last - pos);
         setCityName(newCityName);
 
-        doSimInit();
-
         didLoadCity(filename);
 
         return true;

packages/micropolis-engine/src/initialize.cpp

@@ -84,7 +84,6 @@
 /** Reset many game state variables */
 void Micropolis::initWillStuff()
 {
-    randomlySeedRandom();
     initGraphMax();
     destroyAllSprites();
 

packages/micropolis-engine/src/micropolis.cpp

@@ -738,6 +738,7 @@ void Micropolis::simInit()
     resetMapState();
     resetEditorState();
     clearMap();
+    randomlySeedRandom();
     initWillStuff();
     setFunds(5000);
     setGameLevelFunds(LEVEL_EASY);