How a dimension gets made

Xoshiro256 subStream(const Seed32& seed, std::string_view label) {
    blake3_hasher h;
    blake3_hasher_init(&h);
    blake3_hasher_update(&h, seed.data(), SEED_VISUAL_BYTES);
    blake3_hasher_update(&h, label.data(), label.size());
    uint8_t out[32];
    blake3_hasher_finalize(&h, out, 32);
    return Xoshiro256::fromBytes(out);
}

Tier rollTier(Xoshiro256& r) {
    double u = r.uniform();
    if (u < 0.60) return Tier::Common;
    if (u < 0.85) return Tier::Uncommon;
    if (u < 0.95) return Tier::Rare;
    if (u < 0.99) return Tier::Epic;
    if (u < 0.999) return Tier::Legendary;
    return Tier::Mythic;
}

Unlocks unlocksFor(Tier t) {
    Unlocks u{ 0, 0.55f, false, false, false, 0.f, false, false, 1, false };
    int k = int(t);
    if (k >= 1) { u.extraGens += 1; u.satBerryChance = 0.75f; }
    if (k >= 2) { u.secondBerry = true; u.thirdStop = true; }
    if (k >= 3) { u.forceCompound = true; u.extraGens += 2; u.afterDampBonus = 0.03f; }
    if (k >= 4) { u.forceBleed = true; u.acidOnly = true; u.ringMult = 2; }
    if (k >= 5) { u.gold = true; }   // + the mythic-only family, not written yet
    return u;
}

SeedProps deriveProps(const Seed32& seed, Xoshiro256* shapeRngOut) {
    SeedProps p;
    auto rarityRng = subStream(seed, "rarity");
    auto modeRng = subStream(seed, "mode");
    auto shapeRng = subStream(seed, "shape");
    p.tier = rollTier(rarityRng);
    p.unlocks = unlocksFor(p.tier);
    p.nativeMode = p.unlocks.forceBleed ? Mode::Bleed : rollMode(modeRng);
    p.geo = rollGeoParams(shapeRng);
    p.shapeType = p.unlocks.forceCompound ? 40 : p.geo.type;
    p.family = familyOf(p.shapeType);
    std::memcpy(&p.mutationSeed, seed.data(), 4);
    if (shapeRngOut) *shapeRngOut = shapeRng;
    return p;
}

Dimension rollDimension(const Seed32& seed, int forcedShape, float forcedMood) {
    Dimension d;
    d.seed = seed;
    Xoshiro256 shapeRng = Xoshiro256::fromU64(0);
    SeedProps P = deriveProps(seed, &shapeRng);
    auto mutRng = subStream(seed, "mutation");
    auto skinRng = subStream(seed, "skin");
    auto palRng = subStream(seed, "palette");
    auto lightRng = subStream(seed, "lights");
    auto motionRng = subStream(seed, "motion");
    auto satRng = subStream(seed, "satellites");
    auto foldRng = subStream(seed, "planes");
    auto debRng = subStream(seed, "debris");
    auto partRng = subStream(seed, "particles");
    auto ringRng = subStream(seed, "rings");
    auto bgRng = subStream(seed, "background");
    auto moodRng = subStream(seed, "mood");

    // ---- rarity first: the tier feeds everything after it ----
    d.tier = P.tier;
    d.unlocks = P.unlocks;
    const Unlocks& U = d.unlocks;
    d.runtimeRng = subStream(seed, "runtime");

    // ---- mood ----
    d.moodV = std::pow(float(moodRng.uniform()), 1.6f);
    if (forcedMood >= 0) { d.moodV = std::clamp(forcedMood, 0.f, 1.f); d.moodLocked = true; }
    d.moodSeeded = d.moodV;
    d.moodTarget = d.moodV;

    // ---- mode ----
    d.nativeMode = P.nativeMode;
    d.displayMode = d.nativeMode;

    // ---- palette ----
    PalettePair first = makePair(palRng, U.acidOnly ? 4 : -1);
    d.palC = makeThirdStop(palRng, first);
    d.pal.a = d.pal.fromA = d.pal.toA = first.a;
    d.pal.b = d.pal.fromB = d.pal.toB = first.b;
    d.pal.next = 2.5f + 6 * float(palRng.uniform());
    d.paletteTempo = palRng.range(0.6f, 1.6f);
    d.duoExposure = palRng.range(0.45f, 0.85f);
    d.duoContrast = palRng.range(1.0f, 1.5f);
    d.duoSplit = palRng.range(0.4f, 0.6f);

    // ---- motion ----
    Motion& m = d.motion;
    m.rotX = motionRng.range(-1.2f, 1.2f); m.rotY = motionRng.range(-1.2f, 1.2f); m.rotZ = motionRng.range(-1.2f, 1.2f);
    m.orbitSpeed = motionRng.range(0.1f, 2.5f); m.bobSpeed = motionRng.range(0.1f, 2.5f); m.bobAmp = motionRng.range(0.1f, 1.2f);
    m.waveSpeed = motionRng.range(0.1f, 2.0f); m.waveAmp = motionRng.range(0.05f, 1.0f);
    m.particleSpeed = motionRng.range(0.05f, 1.5f); m.particleSpread = motionRng.range(2.5f, 14);
    m.pulseSpeed = motionRng.range(0.2f, 2.5f); m.pulseAmp = motionRng.range(0.02f, 0.6f);
    m.chaosFactor = motionRng.range(0.1f, 3.0f); m.invertChance = float(motionRng.uniform()); m.brightnessOffset = motionRng.range(-0.3f, 0.5f);

    // ---- lights ----
    glm::vec3 lightPos(std::sin(lightRng.range(0, 2 * PI)) * lightRng.range(7, 13), lightRng.range(8, 16), std::cos(lightRng.range(0, 2 * PI)) * lightRng.range(7, 13));
    d.lightInt[0] = lightRng.range(0.9f, 1.5f);
    glm::vec3 fillPos(-lightPos.x * lightRng.range(0.7f, 1.3f), lightRng.range(-3, 5), -lightPos.z * lightRng.range(0.7f, 1.3f));
    d.lightInt[1] = lightRng.range(0.2f, 0.45f);
    glm::vec3 rimPos(lightRng.range(-4, 4), lightRng.range(2, 6), -lightRng.range(8, 14));
    d.lightInt[2] = lightRng.range(0.4f, 0.8f);
    d.lightDir[0] = glm::normalize(lightPos); d.lightDir[1] = glm::normalize(fillPos); d.lightDir[2] = glm::normalize(rimPos);

    // ---- backdrop ----
    d.bgDensity = bgRng.range(1.5f, 4.0f);
    d.bgSeed = float(bgRng.next() & 0xffffff);

    // ---- shape + lineage ----
    d.geo = P.geo;
    d.shapeType = forcedShape >= 0 ? forcedShape % SHAPE_COUNT : P.shapeType;
    d.family = familyOf(d.shapeType);
    Mesh g = buildShape(d.shapeType, d.geo, shapeRng, 0);
    g = weld(g, 1e-4f);                                   // merged shapes come back with seams, weld before displacing
    d.lineage = mutateLineage(g, mutRng, U.extraGens);
    g.center();
    g.computeVertexNormals();
    d.mainRadius = g.boundingRadius();
    d.mainMesh = std::move(g);
    d.wireAlpha = skinRng.range(0.04f, 0.16f);