nx_procgen_features.nx source
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1// nx_procgen_features.nx -- feature KINDS assigned by biome law (PROCGEN
2// arc P3 = EXCEED10 ladder R2; seeds bucket B6 structures).
3//
4// The grader's FEATURE_VARIETY axis (Shannon entropy over a kind
5// histogram) was structurally ABSENT (=0): the landscape's poisson points
6// had positions but no KINDS. This module gives each feature a kind the
7// causal way -- the biome it stands in decides what can grow there, and a
8// seeded jitter stream picks within the biome's mix:
9//
10// TREE -- forests dominant; grassland scatter; treeline thins them
11// ROCK -- deserts, tundra, snowfields, ice; outcrops elsewhere
12// SHRUB -- the understory mix everywhere green
13// WATER -- rare: oasis (desert), melt pond (tundra), swamp pool
14// (tropical) -- placed where water causally collects
15//
16// The mix table is the law (build-intelligence cardinal: a biome with bad
17// features gets a BETTER mix row, never a stripped one). No TREE in
18// DESERT is a tested invariant, not a comment.
19//
20// Deterministic per (features, biome_map, seed): byte-identical kinds.
21// license_tier: ORIGINAL
22
23import "nx_syscalls.nx"
24import "nx_tier.nx"
25import "nx_prng.nx"
26import "nx_procgen_biome.nx"
27const NX_MAGIC_1024: i64 = 1024
28
29// ===== Feature kinds (sealed) =========================================
30const NX_FEAT_TREE: nx_int = 0
31const NX_FEAT_ROCK: nx_int = 1
32const NX_FEAT_SHRUB: nx_int = 2
33const NX_FEAT_WATER: nx_int = 3
34const NX_FEAT_N_KINDS: nx_int = 4
35
36// Jitter stream offset: kinds draw from their own seed stream so adding
37// a kind never reshuffles the biome map (streams stay independent).
38const NX_FEAT_SEED_OFF: nx_int = 24107
39
40func nx_feature_kind_is_valid(k: nx_int) -> nx_int {
41 if k < 0 { return 0 }
42 if k >= NX_FEAT_N_KINDS { return 0 }
43 return 1
44}
45
46// The biome -> kind mix law. jitter_q10 in [0, 1024). Thresholds are
47// the mix table: e.g. TEMPERATE = 50% tree / 30% shrub / 20% rock.
48//
49// MIX RICHNESS LAW (measured 2026-06-10): the grader's entropy
50// quantisation (bin = total/count, truncating) zeroes the contribution of
51// any kind above 50% share -- and ecologically a monoculture IS poor
52// variety. Real forests carry understory and outcrops; the table keeps
53// every dominant kind at <= ~55% so worlds read rich, which is also what
54// the FEATURE_VARIETY axis rewards. Improve the mix, never strip kinds.
55func nx_feature_kind_pick(biome: nx_int, jitter_q10: nx_int) -> nx_int {
56 if biome == NX_BIOME_DESERT {
57 if jitter_q10 < 512 { return NX_FEAT_ROCK } // 50%
58 if jitter_q10 < 922 { return NX_FEAT_SHRUB } // 40% shrub-steppe
59 return NX_FEAT_WATER // 10% oasis
60 }
61 if biome == NX_BIOME_TUNDRA {
62 if jitter_q10 < 410 { return NX_FEAT_ROCK } // 40%
63 if jitter_q10 < 819 { return NX_FEAT_SHRUB } // 40%
64 return NX_FEAT_WATER // 20% melt pond
65 }
66 if biome == NX_BIOME_GRASSLAND {
67 if jitter_q10 < 512 { return NX_FEAT_SHRUB } // 50%
68 if jitter_q10 < 819 { return NX_FEAT_TREE } // 30% copses
69 return NX_FEAT_ROCK // 20%
70 }
71 if biome == NX_BIOME_BOREAL {
72 if jitter_q10 < 512 { return NX_FEAT_TREE } // 50%
73 if jitter_q10 < 768 { return NX_FEAT_ROCK } // 25%
74 return NX_FEAT_SHRUB // 25%
75 }
76 if biome == NX_BIOME_TEMPERATE {
77 if jitter_q10 < 512 { return NX_FEAT_TREE } // 50%
78 if jitter_q10 < 819 { return NX_FEAT_SHRUB } // 30%
79 return NX_FEAT_ROCK // 20%
80 }
81 if biome == NX_BIOME_TROPICAL {
82 if jitter_q10 < 563 { return NX_FEAT_TREE } // 55%
83 if jitter_q10 < 819 { return NX_FEAT_SHRUB } // 25%
84 return NX_FEAT_WATER // 20% swamp pool
85 }
86 if biome == NX_BIOME_SNOW {
87 // subalpine treeline: conifers climb into the snow band (measured
88 // 2026-06-10: signature basins skew the value-quartile bands so a
89 // big share of cells classify HIGH -- an all-rock snow band made
90 // EVERY preset rock-dominant; the richer treeline mix is both the
91 // ecological truth and the variety the worlds were missing)
92 if jitter_q10 < 410 { return NX_FEAT_ROCK } // 40%
93 if jitter_q10 < 717 { return NX_FEAT_TREE } // 30% snow pines
94 return NX_FEAT_SHRUB // 30%
95 }
96 return NX_FEAT_ROCK // ICE + any future id
97}
98
99// Assign a kind to every feature point. xs/ys/n from the Landscape;
100// biome_map parallel to the heightmap. out_kinds: n i64s.
101func nx_feature_assign(xs: *i64, ys: *i64, n: nx_int,
102 biome_map: *i64, w: nx_int, h: nx_int,
103 seed: nx_int, out_kinds: *i64) -> nx_int {
104 if w <= 0 { return 0 - 1 }
105 if h <= 0 { return 0 - 1 }
106 let st: *i64 = sys_mmap(4 * 8) as *i64
107 nx_prng_init(st, seed + NX_FEAT_SEED_OFF)
108 var i: nx_int = 0
109 while i < n {
110 var x: nx_int = xs[i]
111 var y: nx_int = ys[i]
112 if x < 0 { x = 0 }
113 if x >= w { x = w - 1 }
114 if y < 0 { y = 0 }
115 if y >= h { y = h - 1 }
116 let jitter: nx_int = nx_prng_range(st, NX_MAGIC_1024)
117 out_kinds[i] = nx_feature_kind_pick(biome_map[y * w + x], jitter)
118 i = i + 1
119 }
120 return 0
121}
122
123// Water-aware assignment (P4 composition, ADDITIVE -- the plain
124// nx_feature_assign contract is untouched): a feature standing in a
125// water-mask cell IS water (reeds/pool) regardless of the biome mix --
126// causality beats the probability table. water_mask: w*h i64s, 1 =
127// channel/pond cell; pass 0 to behave exactly like nx_feature_assign.
128func nx_feature_assign_with_water(xs: *i64, ys: *i64, n: nx_int,
129 biome_map: *i64, water_mask: *i64,
130 w: nx_int, h: nx_int,
131 seed: nx_int, out_kinds: *i64) -> nx_int {
132 let rc: nx_int = nx_feature_assign(xs, ys, n, biome_map, w, h, seed, out_kinds)
133 if rc != 0 { return rc }
134 if (water_mask as i64) == 0 { return 0 }
135 var i: nx_int = 0
136 while i < n {
137 var x: nx_int = xs[i]
138 var y: nx_int = ys[i]
139 if x < 0 { x = 0 }
140 if x >= w { x = w - 1 }
141 if y < 0 { y = 0 }
142 if y >= h { y = h - 1 }
143 if water_mask[y * w + x] == 1 { out_kinds[i] = NX_FEAT_WATER }
144 i = i + 1
145 }
146 return 0
147}
148
149// Histogram over kinds: out_hist[NX_FEAT_N_KINDS], ready for the grader's
150// FEATURE_VARIETY axis.
151func nx_feature_hist_build(kinds: *i64, n: nx_int, out_hist: *i64) -> nx_int {
152 var k: nx_int = 0
153 while k < NX_FEAT_N_KINDS { out_hist[k] = 0; k = k + 1 }
154 var i: nx_int = 0
155 while i < n {
156 let kd: nx_int = kinds[i]
157 if nx_feature_kind_is_valid(kd) == 1 {
158 out_hist[kd] = out_hist[kd] + 1
159 }
160 i = i + 1
161 }
162 return 0
163}