nx_procgen_biome.nx source
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1// nx_procgen_biome.nx -- biome map as a CAUSAL DERIVATION from elevation
2// + moisture (PROCGEN arc P2 = EXCEED10 ladder R1; the composed-primitives
3// cardinal: biomes are LAW, not paint).
4//
5// The grader's BIOME_COHERENCE axis (nx_world_quality_grader) was
6// structurally ABSENT (=0) because no generator ever produced a biome map.
7// This module produces one the only honest way: each cell's biome follows
8// from WHERE it is --
9//
10// elevation band = the SAME quartile law the grader checks
11// (low / mid / high / peak over observed range)
12// moisture = a second perlin-fbm field (independent seed stream)
13// picks the biome WITHIN the band, Whittaker-style
14//
15// Band law (must stay in lockstep with _wqg_biome_expected_band):
16// LOW : DESERT (dry) | TUNDRA (wet)
17// MID : GRASSLAND < BOREAL_FOREST < TEMPERATE_FOREST < TROPICAL_RAINFOREST
18// (driest -> wettest)
19// HIGH : SNOW
20// PEAK : ICE
21//
22// Coherence is lawful BY CONSTRUCTION; the grader is the independent
23// instrument that proves the law holds (and catches any future drift
24// between this table and the grader's). Moisture creates the within-band
25// variety that the render/material rung (B4) will consume as color bands.
26//
27// Deterministic per (heightmap, seed): same inputs -> byte-identical map.
28// license_tier: ORIGINAL
29
30import "nx_syscalls.nx"
31import "nx_tier.nx"
32import "nx_perlin.nx"
33
34// ===== Biome IDs (sealed; values fixed by the grader's expected-band law)
35const NX_BIOME_TUNDRA: nx_int = 0
36const NX_BIOME_BOREAL: nx_int = 1
37const NX_BIOME_GRASSLAND: nx_int = 4
38const NX_BIOME_TEMPERATE: nx_int = 5
39const NX_BIOME_DESERT: nx_int = 8
40const NX_BIOME_TROPICAL: nx_int = 11
41const NX_BIOME_SNOW: nx_int = 12
42const NX_BIOME_ICE: nx_int = 13
43// Histogram length covering all IDs above (grader takes ids 0..13).
44const NX_BIOME_ID_SPAN: nx_int = 14
45
46// Moisture thresholds (Q10, fbm band is ~[-1024, 1024]).
47const NX_BIOME_MOIST_DRY: nx_int = 0 - 256
48const NX_BIOME_MOIST_MID: nx_int = 0
49const NX_BIOME_MOIST_WET: nx_int = 256
50
51// Seed offset for the moisture stream: biome moisture must be independent
52// of the heightmap's noise stream but derived from the SAME world seed
53// (one seed reproduces the whole world).
54const NX_BIOME_MOISTURE_SEED_OFF: nx_int = 9173
55
56// Moisture field sampling (matches the heightmap's cell step so moisture
57// patches have landscape-scale coherence).
58const NX_BIOME_MOIST_STEP_Q10: nx_int = 102
59const NX_BIOME_MOIST_OCTAVES: nx_int = 3
60const NX_BIOME_MOIST_PERSIST: nx_int = 512
61
62func nx_biome_is_valid(b: nx_int) -> nx_int {
63 if b == NX_BIOME_TUNDRA { return 1 }
64 if b == NX_BIOME_BOREAL { return 1 }
65 if b == NX_BIOME_GRASSLAND { return 1 }
66 if b == NX_BIOME_TEMPERATE { return 1 }
67 if b == NX_BIOME_DESERT { return 1 }
68 if b == NX_BIOME_TROPICAL { return 1 }
69 if b == NX_BIOME_SNOW { return 1 }
70 if b == NX_BIOME_ICE { return 1 }
71 return 0
72}
73
74// Elevation band 0..3 -- IDENTICAL comparisons to the grader's
75// _wqg_biome_coherence_score so coherence can never drift by construction.
76func nx_biome_band(v: nx_int, hmin: nx_int, range: nx_int) -> nx_int {
77 let low_max: nx_int = hmin + range / 4
78 let mid_max: nx_int = hmin + (range * 2) / 4
79 let hi_max: nx_int = hmin + (range * 3) / 4
80 var band: nx_int = 0
81 if v > low_max { band = 1 }
82 if v > mid_max { band = 2 }
83 if v > hi_max { band = 3 }
84 return band
85}
86
87// The classification law: (band, moisture) -> biome. Pure, table-shaped,
88// no state -- the Whittaker diagram as a function.
89func nx_biome_pick(band: nx_int, moisture_q10: nx_int) -> nx_int {
90 if band == 0 {
91 if moisture_q10 < NX_BIOME_MOIST_MID { return NX_BIOME_DESERT }
92 return NX_BIOME_TUNDRA
93 }
94 if band == 1 {
95 if moisture_q10 < NX_BIOME_MOIST_DRY { return NX_BIOME_GRASSLAND }
96 if moisture_q10 < NX_BIOME_MOIST_MID { return NX_BIOME_BOREAL }
97 if moisture_q10 < NX_BIOME_MOIST_WET { return NX_BIOME_TEMPERATE }
98 return NX_BIOME_TROPICAL
99 }
100 if band == 2 { return NX_BIOME_SNOW }
101 return NX_BIOME_ICE
102}
103
104// Build the biome map for a heightmap. out_map: w*h i64s, parallel to
105// heightmap. Deterministic per (heightmap contents, seed).
106// Flat map (range 0): every cell is band 0 -> moisture still differentiates
107// DESERT/TUNDRA (the grader skips coherence on range 0; we stay valid).
108func nx_biome_map_build(heightmap: *i64, w: nx_int, h: nx_int,
109 seed: nx_int, out_map: *i64) -> nx_int {
110 if w <= 0 { return 0 - 1 }
111 if h <= 0 { return 0 - 1 }
112 let n: nx_int = w * h
113
114 // pass 1: observed range (the band law is relative, like the grader's)
115 var hmin: nx_int = heightmap[0]
116 var hmax: nx_int = heightmap[0]
117 var i: nx_int = 0
118 while i < n {
119 let v: nx_int = heightmap[i]
120 if v < hmin { hmin = v }
121 if v > hmax { hmax = v }
122 i = i + 1
123 }
124 let range: nx_int = hmax - hmin
125
126 // pass 2: moisture stream + classification
127 let ms: *PerlinState = nx_perlin_alloc(seed + NX_BIOME_MOISTURE_SEED_OFF)
128 var y: nx_int = 0
129 while y < h {
130 var x: nx_int = 0
131 while x < w {
132 let idx: nx_int = y * w + x
133 let m: nx_int = nx_perlin_fbm_2d(ms,
134 x * NX_BIOME_MOIST_STEP_Q10,
135 y * NX_BIOME_MOIST_STEP_Q10,
136 NX_BIOME_MOIST_OCTAVES,
137 NX_BIOME_MOIST_PERSIST)
138 let band: nx_int = nx_biome_band(heightmap[idx], hmin, range)
139 out_map[idx] = nx_biome_pick(band, m)
140 x = x + 1
141 }
142 y = y + 1
143 }
144 return 0
145}