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May 2, 2026
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feat: generalize biome decoration rules #635

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28c8e54
feat: generalize biome decoration rules
MichaelFisher1997 May 2, 2026
02fdcaf
fix: guard decoration placement height
MichaelFisher1997 May 2, 2026
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70 changes: 39 additions & 31 deletions modules/world-worldgen/src/biome_registry.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

const std = @import("std");
const BlockType = @import("world-core").BlockType;
const DecorationRule = @import("decoration_types.zig").DecorationRule;
const tree_registry = @import("tree_registry.zig");
pub const TreeType = tree_registry.TreeType;

Expand Down Expand Up @@ -43,16 +44,8 @@ pub const ColorTints = struct {

/// Vegetation profile for biome-driven placement
pub const VegetationProfile = struct {
tree_types: []const TreeType = &.{.oak},
tree_density: f32 = 0.05, // Probability per attempt
bush_density: f32 = 0.0,
grass_density: f32 = 0.0,
cactus_density: f32 = 0.0,
dead_bush_density: f32 = 0.0,
bamboo_density: f32 = 0.0,
melon_density: f32 = 0.0,
red_mushroom_density: f32 = 0.0,
brown_mushroom_density: f32 = 0.0,
tree_types: []const TreeType = &.{},
decoration_rules: []const DecorationRule = &.{},
};

/// Terrain modifiers applied during height computation
Expand Down Expand Up @@ -233,7 +226,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = 0.0, .max = 0.20 },
.priority = 2,
.surface = .{ .top = .gravel, .filler = .gravel, .depth_range = 4 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0 },
.vegetation = .{ .tree_types = &.{} },
.colors = .{ .water = .{ 0.1, 0.2, 0.5 } },
},
.{
Expand All @@ -245,7 +238,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = 0.0, .max = 0.35 },
.priority = 1,
.surface = .{ .top = .sand, .filler = .sand, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0 },
.vegetation = .{ .tree_types = &.{} },
},
.{
.id = .beach,
Expand All @@ -257,7 +250,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.max_slope = 2,
.priority = 10,
.surface = .{ .top = .sand, .filler = .sand, .depth_range = 2 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0 },
.vegetation = .{ .tree_types = &.{} },
},

// === Land Biomes (continentalness > 0.45) ===
Expand All @@ -271,7 +264,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = Range.any(),
.priority = 0, // Fallback
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{.sparse_oak}, .tree_density = 0.02, .grass_density = 0.3 },
.vegetation = .{ .tree_types = &.{.sparse_oak}, .decoration_rules = &.{.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.3 }} },
.terrain = .{ .height_amplitude = 0.7, .smoothing = 0.2 },
},
.{
Expand All @@ -284,7 +277,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = .{ .min = 0.0, .max = 0.60 },
.priority = 5,
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{ .oak, .birch, .dense_oak }, .tree_density = 0.12, .bush_density = 0.05, .grass_density = 0.4 },
.vegetation = .{ .tree_types = &.{ .oak, .birch, .dense_oak }, .decoration_rules = &.{.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.4 }} },
.colors = .{ .grass = .{ 0.18, 0.64, 0.16 }, .foliage = .{ 0.12, 0.52, 0.12 } },
},
.{
Expand All @@ -296,7 +289,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = 0.45, .max = 1.0 },
.priority = 6,
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{.spruce}, .tree_density = 0.10, .grass_density = 0.2 },
.vegetation = .{ .tree_types = &.{.spruce}, .decoration_rules = &.{.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.2 }} },
.colors = .{ .grass = .{ 0.24, 0.56, 0.24 }, .foliage = .{ 0.18, 0.46, 0.18 } },
},
.{
Expand All @@ -311,7 +304,10 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.max_slope = 4,
.priority = 6,
.surface = .{ .top = .sand, .filler = .sand, .depth_range = 6 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0, .cactus_density = 0.015, .dead_bush_density = 0.02 },
.vegetation = .{ .tree_types = &.{}, .decoration_rules = &.{
.{ .block = .cactus, .place_on = &.{.sand}, .chance = 0.015 },
.{ .block = .dead_bush, .place_on = &.{.sand}, .chance = 0.02 },
} },
.terrain = .{ .height_amplitude = 0.5, .smoothing = 0.4 },
.colors = .{ .grass = .{ 0.75, 0.70, 0.35 } },
},
Expand All @@ -326,7 +322,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.max_slope = 3,
.priority = 5,
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 2 },
.vegetation = .{ .tree_types = &.{.swamp_oak}, .tree_density = 0.08 },
.vegetation = .{ .tree_types = &.{.swamp_oak} },
.terrain = .{ .clamp_to_sea_level = true, .height_offset = -2 },
.colors = .{
.grass = .{ 0.24, 0.54, 0.20 },
Expand All @@ -345,7 +341,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.max_slope = 255,
.priority = 4,
.surface = .{ .top = .snow_block, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{.spruce}, .tree_density = 0.01 },
.vegetation = .{ .tree_types = &.{.spruce} },
.colors = .{ .grass = .{ 0.7, 0.75, 0.8 } },
},

Expand All @@ -362,7 +358,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.min_ridge_mask = 0.1,
.priority = 2,
.surface = .{ .top = .stone, .filler = .stone, .depth_range = 1 },
.vegetation = .{ .tree_types = &.{.sparse_oak}, .tree_density = 0 },
.vegetation = .{ .tree_types = &.{.sparse_oak} },
.terrain = .{ .height_amplitude = 1.5 },
},
.{
Expand All @@ -377,7 +373,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.max_slope = 255,
.priority = 2,
.surface = .{ .top = .snow_block, .filler = .stone, .depth_range = 1 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0 },
.vegetation = .{ .tree_types = &.{} },
.terrain = .{ .height_amplitude = 1.4 },
.colors = .{ .grass = .{ 0.85, 0.90, 0.95 } },
},
Expand All @@ -392,7 +388,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = 0.45, .max = 0.60 }, // Coastal swamp
.priority = 6,
.surface = .{ .top = .mud, .filler = .mud, .depth_range = 4 },
.vegetation = .{ .tree_types = &.{.mangrove}, .tree_density = 0.15 },
.vegetation = .{ .tree_types = &.{.mangrove} },
.terrain = .{ .clamp_to_sea_level = true, .height_offset = -1 },
.colors = .{ .grass = .{ 0.26, 0.58, 0.18 }, .foliage = .{ 0.22, 0.52, 0.16 }, .water = .{ 0.16, 0.38, 0.30 } },
},
Expand All @@ -405,7 +401,10 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = 0.60, .max = 1.0 }, // Inland
.priority = 5,
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{.jungle}, .tree_density = 0.20, .bamboo_density = 0.08, .melon_density = 0.04 },
.vegetation = .{ .tree_types = &.{.jungle}, .decoration_rules = &.{
.{ .block = .bamboo, .place_on = &.{.grass}, .chance = 0.08 },
.{ .block = .melon, .place_on = &.{.grass}, .chance = 0.04 },
} },
.colors = .{ .grass = .{ 0.10, 0.76, 0.08 }, .foliage = .{ 0.08, 0.62, 0.08 } },
},
.{
Expand All @@ -417,7 +416,10 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = 0.55, .max = 1.0 }, // Inland (less restrictive)
.priority = 5, // Higher priority to win over plains in hot zones
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{.acacia}, .tree_density = 0.015, .grass_density = 0.5, .dead_bush_density = 0.01 },
.vegetation = .{ .tree_types = &.{.acacia}, .decoration_rules = &.{
.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.5 },
.{ .block = .dead_bush, .place_on = &.{.grass}, .chance = 0.01 },
} },
.colors = .{ .grass = .{ 0.55, 0.55, 0.30 }, .foliage = .{ 0.50, 0.50, 0.28 } },
},
.{
Expand All @@ -430,7 +432,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = .{ .min = 0.4, .max = 1.0 },
.priority = 6,
.surface = .{ .top = .red_sand, .filler = .terracotta, .depth_range = 5 },
.vegetation = .{ .cactus_density = 0.02 },
.vegetation = .{ .tree_types = &.{}, .decoration_rules = &.{.{ .block = .cactus, .place_on = &.{.red_sand}, .chance = 0.02 }} },
.colors = .{ .grass = .{ 0.5, 0.4, 0.3 } },
},
.{
Expand All @@ -442,7 +444,10 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.max_height = 50,
.priority = 20,
.surface = .{ .top = .mycelium, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{ .huge_red_mushroom, .huge_brown_mushroom }, .tree_density = 0.05, .red_mushroom_density = 0.1, .brown_mushroom_density = 0.1 },
.vegetation = .{ .tree_types = &.{ .huge_red_mushroom, .huge_brown_mushroom }, .decoration_rules = &.{
.{ .block = .red_mushroom_block, .place_on = &.{.mycelium}, .chance = 0.1 },
.{ .block = .brown_mushroom_block, .place_on = &.{.mycelium}, .chance = 0.1 },
} },
.colors = .{ .grass = .{ 0.4, 0.8, 0.4 } },
},
.{
Expand All @@ -455,7 +460,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.continentalness = .{ .min = -1.0, .max = -0.5 },
.priority = 15,
.surface = .{ .top = .sand, .filler = .sand, .depth_range = 2 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0 },
.vegetation = .{ .tree_types = &.{} },
},

// === Transition Micro-Biomes ===
Expand All @@ -472,7 +477,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = .{ .min = 0.30, .max = 0.80 },
.priority = 0, // Lowest priority
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{ .sparse_oak, .spruce }, .tree_density = 0.08, .grass_density = 0.4 },
.vegetation = .{ .tree_types = &.{ .sparse_oak, .spruce }, .decoration_rules = &.{.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.4 }} },
.terrain = .{ .height_amplitude = 1.1, .smoothing = 0.1 },
.colors = .{ .grass = .{ 0.24, 0.62, 0.22 }, .foliage = .{ 0.18, 0.50, 0.16 } },
},
Expand All @@ -486,7 +491,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = .{ .min = 0.0, .max = 0.30 },
.priority = 0, // Lowest priority
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 2 },
.vegetation = .{ .tree_types = &.{.swamp_oak}, .tree_density = 0.04, .grass_density = 0.5 },
.vegetation = .{ .tree_types = &.{.swamp_oak}, .decoration_rules = &.{.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.5 }} },
.terrain = .{ .height_offset = -1, .smoothing = 0.3 },
.colors = .{
.grass = .{ 0.20, 0.58, 0.20 },
Expand All @@ -504,7 +509,10 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = .{ .min = 0.0, .max = 0.40 },
.priority = 0, // Lowest priority
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{.acacia}, .tree_density = 0.005, .grass_density = 0.3, .dead_bush_density = 0.02 },
.vegetation = .{ .tree_types = &.{.acacia}, .decoration_rules = &.{
.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.3 },
.{ .block = .dead_bush, .place_on = &.{.grass}, .chance = 0.02 },
} },
.terrain = .{ .height_amplitude = 0.6, .smoothing = 0.25 },
.colors = .{ .grass = .{ 0.55, 0.50, 0.28 } }, // Less yellow, more natural
},
Expand All @@ -518,7 +526,7 @@ pub const BIOME_REGISTRY: []const BiomeDefinition = &.{
.ruggedness = .{ .min = 0.0, .max = 0.35 },
.priority = 0, // Lowest priority
.surface = .{ .top = .grass, .filler = .dirt, .depth_range = 3 },
.vegetation = .{ .tree_types = &.{}, .tree_density = 0, .grass_density = 0.4 }, // No trees
.vegetation = .{ .tree_types = &.{}, .decoration_rules = &.{.{ .block = .tall_grass, .place_on = &.{.grass}, .chance = 0.4 }} }, // No trees
.terrain = .{ .height_amplitude = 0.5, .smoothing = 0.3 },
.colors = .{ .grass = .{ 0.24, 0.66, 0.24 }, .foliage = .{ 0.18, 0.52, 0.16 } },
},
Expand Down
24 changes: 22 additions & 2 deletions modules/world-worldgen/src/decoration_registry.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ pub const SimpleDecoration = types.SimpleDecoration;
pub const SchematicBlock = types.SchematicBlock;
pub const Schematic = types.Schematic;
pub const SchematicDecoration = types.SchematicDecoration;
pub const DecorationRule = types.DecorationRule;
pub const Decoration = types.Decoration;
pub const DecorationProvider = @import("decoration_provider.zig").DecorationProvider;
pub const DecorationContext = @import("decoration_provider.zig").DecorationProvider.DecorationContext;
Expand Down Expand Up @@ -107,6 +108,7 @@ fn variantAllowed(variant: f32, allow_subbiomes: bool, min: f32, max: f32) bool

const Chunk = world_core.Chunk;
const CHUNK_SIZE_X = world_core.CHUNK_SIZE_X;
const CHUNK_SIZE_Y = world_core.CHUNK_SIZE_Y;
const CHUNK_SIZE_Z = world_core.CHUNK_SIZE_Z;

pub const StandardDecorationProvider = struct {
Expand Down Expand Up @@ -169,13 +171,31 @@ pub const StandardDecorationProvider = struct {

// 1. Static decorations (flowers, grass)
if (chooseStaticSimpleDecoration(biome, surface_block, variant, allow_subbiomes, veg_mult, random)) |simple| {
chunk.setBlock(local_x, @intCast(surface_y + 1), local_z, simple.block);
const place_y = surface_y + 1;
if (place_y >= 0 and place_y < CHUNK_SIZE_Y) {
chunk.setBlock(local_x, @intCast(place_y), local_z, simple.block);
}
}

// 2. Dynamic Tree Registry (from Biome Definition)
// 2. Biome-defined block decoration rules
const biome_def = biome_mod.getBiomeDefinition(biome);
const vegetation = biome_def.vegetation;

for (vegetation.decoration_rules) |rule| {
if (!rule.isAllowed(surface_block, surface_y, variant, allow_subbiomes)) continue;

const prob = @min(1.0, rule.chance * veg_mult);
if (random.float(f32) >= prob) continue;

const place_y = surface_y + 1;
if (place_y < 0 or place_y >= CHUNK_SIZE_Y) continue;
if (chunk.getBlockSafe(@intCast(local_x), place_y, @intCast(local_z)) != .air) continue;

chunk.setBlock(local_x, @intCast(place_y), local_z, rule.block);
break;
}

// 3. Dynamic Tree Registry (from Biome Definition)
if (vegetation.tree_types.len > 0) {
for (vegetation.tree_types) |tree_type| {
if (tree_registry.getTreeDefinition(tree_type)) |tree_def| {
Expand Down
17 changes: 17 additions & 0 deletions modules/world-worldgen/src/decoration_types.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,23 @@ pub const SchematicDecoration = struct {
}
};

pub const DecorationRule = struct {
block: BlockType,
place_on: []const BlockType,
chance: f32,
y_min: i32 = 1,
y_max: i32 = 256,
variant_min: f32 = -1.0,
variant_max: f32 = 1.0,

pub fn isAllowed(self: DecorationRule, surface_block: BlockType, surface_y: i32, variant: f32, allow_subbiomes: bool) bool {
if (!isBlockAllowed(self.place_on, surface_block)) return false;
if (surface_y + 1 < self.y_min or surface_y + 1 > self.y_max) return false;
if (allow_subbiomes) return variant >= self.variant_min and variant <= self.variant_max;
return self.variant_min == -1.0 and self.variant_max == 1.0;
}
};

pub const Decoration = union(enum) {
simple: SimpleDecoration,
schematic: SchematicDecoration,
Expand Down
4 changes: 2 additions & 2 deletions src/worldgen_tests.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -218,8 +218,8 @@ test "WorldGen stable chunk fingerprints for known seed" {
};

const expected = [_]u64{
12740687495258888450,
14029817033549788541,
16067496184749289293,
10106071382427144696,
4422434882344650145,
};

Expand Down
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