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| 1 | +//! Land-cover-driven biome assignment for Java Anvil chunks (1.18+). |
| 2 | +
|
| 3 | +use crate::coordinate_system::cartesian::XZPoint; |
| 4 | +use crate::ground::Ground; |
| 5 | +use crate::land_cover::{ |
| 6 | + LC_BARE, LC_BUILT_UP, LC_CROPLAND, LC_GRASSLAND, LC_MANGROVES, LC_MOSS, LC_SHRUBLAND, |
| 7 | + LC_SNOW_ICE, LC_TREE_COVER, LC_WATER, LC_WETLAND, |
| 8 | +}; |
| 9 | +use fastnbt::{LongArray, Value}; |
| 10 | +use std::collections::HashMap; |
| 11 | + |
| 12 | +/// Map an ESA WorldCover class to a Minecraft biome ID. |
| 13 | +pub fn biome_for_class(lc: u8, lat_deg: f64, water_dist: u8) -> &'static str { |
| 14 | + let abs_lat = lat_deg.abs(); |
| 15 | + match lc { |
| 16 | + LC_TREE_COVER => { |
| 17 | + if abs_lat > 55.0 { |
| 18 | + "minecraft:taiga" |
| 19 | + } else if abs_lat < 23.5 { |
| 20 | + "minecraft:jungle" |
| 21 | + } else { |
| 22 | + "minecraft:forest" |
| 23 | + } |
| 24 | + } |
| 25 | + LC_SHRUBLAND => "minecraft:savanna", |
| 26 | + LC_GRASSLAND | LC_CROPLAND | LC_BUILT_UP => "minecraft:plains", |
| 27 | + LC_BARE => "minecraft:desert", |
| 28 | + LC_SNOW_ICE => "minecraft:snowy_plains", |
| 29 | + LC_WATER => { |
| 30 | + if water_dist >= 8 { |
| 31 | + "minecraft:ocean" |
| 32 | + } else { |
| 33 | + "minecraft:river" |
| 34 | + } |
| 35 | + } |
| 36 | + LC_WETLAND => "minecraft:swamp", |
| 37 | + LC_MANGROVES => "minecraft:mangrove_swamp", |
| 38 | + LC_MOSS => "minecraft:taiga", |
| 39 | + _ => "minecraft:plains", |
| 40 | + } |
| 41 | +} |
| 42 | + |
| 43 | +pub type ChunkBiomeNbt = Value; |
| 44 | + |
| 45 | +/// Build the `biomes` compound for one chunk, sampling LC at a 4x4 grid |
| 46 | +/// (4-block resolution) and packing into the Anvil 1.18+ palette+data layout. |
| 47 | +pub fn build_chunk_biome_nbt( |
| 48 | + chunk_x: i32, |
| 49 | + chunk_z: i32, |
| 50 | + ground: Option<&Ground>, |
| 51 | + center_lat_deg: f64, |
| 52 | +) -> ChunkBiomeNbt { |
| 53 | + let mut names: [&'static str; 16] = ["minecraft:plains"; 16]; |
| 54 | + |
| 55 | + if let Some(g) = ground { |
| 56 | + for zi in 0..4i32 { |
| 57 | + for xi in 0..4i32 { |
| 58 | + let world_x = chunk_x * 16 + xi * 4 + 2; |
| 59 | + let world_z = chunk_z * 16 + zi * 4 + 2; |
| 60 | + let coord = XZPoint::new(world_x, world_z); |
| 61 | + let lc = g.cover_class(coord); |
| 62 | + let wd = g.water_distance(coord); |
| 63 | + names[(zi * 4 + xi) as usize] = biome_for_class(lc, center_lat_deg, wd); |
| 64 | + } |
| 65 | + } |
| 66 | + } |
| 67 | + |
| 68 | + let mut palette: Vec<&'static str> = Vec::with_capacity(4); |
| 69 | + let mut indices: [u8; 16] = [0; 16]; |
| 70 | + for (i, &name) in names.iter().enumerate() { |
| 71 | + let idx = match palette.iter().position(|p| *p == name) { |
| 72 | + Some(idx) => idx, |
| 73 | + None => { |
| 74 | + palette.push(name); |
| 75 | + palette.len() - 1 |
| 76 | + } |
| 77 | + }; |
| 78 | + indices[i] = idx as u8; |
| 79 | + } |
| 80 | + |
| 81 | + let palette_value = Value::List( |
| 82 | + palette |
| 83 | + .iter() |
| 84 | + .map(|&s| Value::String(s.to_string())) |
| 85 | + .collect(), |
| 86 | + ); |
| 87 | + |
| 88 | + if palette.len() <= 1 { |
| 89 | + let mut map = HashMap::with_capacity(1); |
| 90 | + map.insert("palette".to_string(), palette_value); |
| 91 | + return Value::Compound(map); |
| 92 | + } |
| 93 | + |
| 94 | + let bits = bits_per_index(palette.len()); |
| 95 | + let data = pack_biome_indices(&indices, bits); |
| 96 | + |
| 97 | + let mut map = HashMap::with_capacity(2); |
| 98 | + map.insert("palette".to_string(), palette_value); |
| 99 | + map.insert("data".to_string(), Value::LongArray(LongArray::new(data))); |
| 100 | + Value::Compound(map) |
| 101 | +} |
| 102 | + |
| 103 | +fn bits_per_index(palette_size: usize) -> u32 { |
| 104 | + if palette_size <= 1 { |
| 105 | + 0 |
| 106 | + } else { |
| 107 | + (palette_size - 1).ilog2() + 1 |
| 108 | + } |
| 109 | +} |
| 110 | + |
| 111 | +// Post-1.16 packing: values do not straddle long boundaries. |
| 112 | +fn pack_biome_indices(indices_16: &[u8; 16], bits: u32) -> Vec<i64> { |
| 113 | + debug_assert!((1..=6).contains(&bits)); |
| 114 | + let bits = bits as usize; |
| 115 | + let vals_per_long = 64 / bits; |
| 116 | + let num_longs = 64usize.div_ceil(vals_per_long); |
| 117 | + let mask: u64 = (1u64 << bits) - 1; |
| 118 | + |
| 119 | + let mut longs = vec![0u64; num_longs]; |
| 120 | + for cell in 0..64usize { |
| 121 | + // xz biomes repeat across y, so xz_idx = cell % 16. |
| 122 | + let xz_idx = cell % 16; |
| 123 | + let value = (indices_16[xz_idx] as u64) & mask; |
| 124 | + let long_idx = cell / vals_per_long; |
| 125 | + let bit_offset = (cell % vals_per_long) * bits; |
| 126 | + longs[long_idx] |= value << bit_offset; |
| 127 | + } |
| 128 | + longs.into_iter().map(|u| u as i64).collect() |
| 129 | +} |
| 130 | + |
| 131 | +#[cfg(test)] |
| 132 | +mod tests { |
| 133 | + use super::*; |
| 134 | + |
| 135 | + #[test] |
| 136 | + fn bits_per_index_table() { |
| 137 | + assert_eq!(bits_per_index(1), 0); |
| 138 | + assert_eq!(bits_per_index(2), 1); |
| 139 | + assert_eq!(bits_per_index(3), 2); |
| 140 | + assert_eq!(bits_per_index(4), 2); |
| 141 | + assert_eq!(bits_per_index(5), 3); |
| 142 | + assert_eq!(bits_per_index(8), 3); |
| 143 | + assert_eq!(bits_per_index(9), 4); |
| 144 | + assert_eq!(bits_per_index(16), 4); |
| 145 | + } |
| 146 | + |
| 147 | + #[test] |
| 148 | + fn pack_alternating_1bit_fits_one_long() { |
| 149 | + let mut indices = [0u8; 16]; |
| 150 | + for (i, v) in indices.iter_mut().enumerate() { |
| 151 | + *v = (i % 2) as u8; |
| 152 | + } |
| 153 | + let longs = pack_biome_indices(&indices, 1); |
| 154 | + assert_eq!(longs.len(), 1); |
| 155 | + let expected: u64 = (0..64u64).fold(0, |acc, c| acc | ((c % 2) << c)); |
| 156 | + assert_eq!(longs[0] as u64, expected); |
| 157 | + } |
| 158 | + |
| 159 | + #[test] |
| 160 | + fn pack_three_biomes_uses_two_longs() { |
| 161 | + let mut indices = [0u8; 16]; |
| 162 | + for (i, v) in indices.iter_mut().enumerate() { |
| 163 | + *v = (i % 3) as u8; |
| 164 | + } |
| 165 | + let longs = pack_biome_indices(&indices, 2); |
| 166 | + assert_eq!(longs.len(), 2); |
| 167 | + } |
| 168 | + |
| 169 | + #[test] |
| 170 | + fn pack_three_bit_pads_to_four_longs() { |
| 171 | + let indices = [4u8; 16]; |
| 172 | + let longs = pack_biome_indices(&indices, 3); |
| 173 | + assert_eq!(longs.len(), 4); |
| 174 | + } |
| 175 | + |
| 176 | + #[test] |
| 177 | + fn no_ground_yields_plains_palette() { |
| 178 | + let nbt = build_chunk_biome_nbt(0, 0, None, 0.0); |
| 179 | + match nbt { |
| 180 | + Value::Compound(map) => { |
| 181 | + assert!(map.contains_key("palette")); |
| 182 | + assert!(!map.contains_key("data")); |
| 183 | + } |
| 184 | + _ => panic!("expected compound"), |
| 185 | + } |
| 186 | + } |
| 187 | + |
| 188 | + #[test] |
| 189 | + fn latitude_drives_tree_biome() { |
| 190 | + assert_eq!(biome_for_class(LC_TREE_COVER, 0.0, 0), "minecraft:jungle"); |
| 191 | + assert_eq!(biome_for_class(LC_TREE_COVER, 40.0, 0), "minecraft:forest"); |
| 192 | + assert_eq!(biome_for_class(LC_TREE_COVER, 60.0, 0), "minecraft:taiga"); |
| 193 | + assert_eq!(biome_for_class(LC_TREE_COVER, -60.0, 0), "minecraft:taiga"); |
| 194 | + } |
| 195 | + |
| 196 | + #[test] |
| 197 | + fn water_distance_drives_river_vs_ocean() { |
| 198 | + assert_eq!(biome_for_class(LC_WATER, 0.0, 1), "minecraft:river"); |
| 199 | + assert_eq!(biome_for_class(LC_WATER, 0.0, 7), "minecraft:river"); |
| 200 | + assert_eq!(biome_for_class(LC_WATER, 0.0, 8), "minecraft:ocean"); |
| 201 | + } |
| 202 | +} |
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