83 lines
3 KiB
JavaScript
83 lines
3 KiB
JavaScript
// Determinism guard for the shared character simulation. The client predictor
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// and the authoritative server run the EXACT same stepCharacterMovement; if it
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// were non-deterministic (a stray Math.random / Date, or an order-dependent
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// reduce) prediction would rubber-band and could never reconcile. This is also
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// the regression net for the upcoming GC/scratch-pool perf rewrites: the pinned
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// hash must not change unless physics behaviour is intentionally changed.
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import { describe, it, expect } from 'vitest';
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import { createRequire } from 'node:module';
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const require = createRequire(import.meta.url);
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const shared = require('../shared/lib/main.js');
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const { vec2 } = require('../shared/node_modules/gl-matrix');
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const {
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stepCharacterMovement,
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resolveCircleMovement,
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headRadius,
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feetRadius,
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headOffset,
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leftFootOffset,
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rightFootOffset,
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} = shared;
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const makeBody = (center, radius) => ({
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center: vec2.clone(center),
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radius,
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velocity: vec2.create(),
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lastNormal: vec2.fromValues(0, 1),
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restitution: 0,
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});
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// A free-space world (no planets): the body is driven purely by the movement
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// input force, posture springs and momentum decay — enough to exercise the
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// deterministic core without coupling the test to planet SDF geometry.
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const emptyWorld = {
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groundsNear: () => [],
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stepBody: (body, dt) => {
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resolveCircleMovement(body, dt, []);
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return undefined;
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},
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};
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const stepSeconds = 1 / 200;
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// Run a fixed, scripted input sequence through the shared sim and return a
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// stable string snapshot of the final pose + carried momentum.
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const runSimulation = () => {
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const start = vec2.fromValues(100, 100);
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const state = {
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head: makeBody(vec2.add(vec2.create(), start, headOffset), headRadius),
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leftFoot: makeBody(vec2.add(vec2.create(), start, leftFootOffset), feetRadius),
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rightFoot: makeBody(vec2.add(vec2.create(), start, rightFootOffset), feetRadius),
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direction: 0,
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currentPlanet: undefined,
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secondsSinceOnSurface: 1,
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bodyVelocity: vec2.create(),
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};
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for (let i = 0; i < 300; i++) {
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const angle = i * 0.1;
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const input = vec2.fromValues(Math.cos(angle), Math.sin(angle));
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stepCharacterMovement(state, emptyWorld, input, stepSeconds);
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}
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const round = (v) => Math.round(v * 1000) / 1000;
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return JSON.stringify({
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head: [round(state.head.center[0]), round(state.head.center[1])],
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leftFoot: [round(state.leftFoot.center[0]), round(state.leftFoot.center[1])],
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rightFoot: [round(state.rightFoot.center[0]), round(state.rightFoot.center[1])],
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bodyVelocity: [round(state.bodyVelocity[0]), round(state.bodyVelocity[1])],
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});
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};
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describe('shared character simulation determinism', () => {
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it('produces identical output across independent runs', () => {
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expect(runSimulation()).toBe(runSimulation());
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});
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it('matches the pinned reference pose (changes only with intentional physics edits)', () => {
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// Regression pin — update deliberately when physics behaviour changes.
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expect(runSimulation()).toMatchSnapshot();
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});
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});
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