resource, world: implement fallback to plains for unknown biomes

Closes #63

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 ## [Unreleased] - ReleaseDate
 
+### Changed
+
+- Unknown biome types (from not yet supported or modded versions of Minecraft)
+  will now use plains biome colors as a fallback instead of resulting in water,
+  grass and foliage blocks to be rendered as transparent pixels
+
 ## [2.4.0] - 2025-01-11
 
 ### Added

crates/resource/src/lib.rs

@@ -247,6 +247,8 @@ pub struct BiomeTypes {
 	biome_map: HashMap<String, &'static Biome>,
 	/// Array used to look up old numeric biome IDs
 	legacy_biomes: Box<[&'static Biome; 256]>,
+	/// Fallback for unknown (new/modded) biomes
+	fallback_biome: &'static Biome,
 }
 
 impl Default for BiomeTypes {
@@ -273,9 +275,12 @@ impl Default for BiomeTypes {
 			.try_into()
 			.unwrap();
 
+		let fallback_biome = *biome_map.get("plains").expect("Plains biome undefined");
+
 		Self {
 			biome_map,
 			legacy_biomes,
+			fallback_biome,
 		}
 	}
 }
@@ -293,4 +298,10 @@ impl BiomeTypes {
 	pub fn get_legacy(&self, id: u8) -> Option<&Biome> {
 		Some(self.legacy_biomes[id as usize])
 	}
+
+	/// Returns the fallback for unknown (new/modded) biomes
+	#[inline]
+	pub fn get_fallback(&self) -> &Biome {
+		self.fallback_biome
+	}
 }

src/core/common.rs

@@ -25,7 +25,7 @@ use crate::{
 ///
 /// Increase when the generation of processed regions from region data changes
 /// (usually because of updated resource data)
-pub const REGION_FILE_META_VERSION: FileMetaVersion = FileMetaVersion(3);
+pub const REGION_FILE_META_VERSION: FileMetaVersion = FileMetaVersion(4);
 
 /// MinedMap map tile data version number
 ///

src/world/layer.rs

@@ -97,7 +97,8 @@ impl LayerEntry<'_> {
 
 		if self.is_empty() {
 			*self.block = Some(block_type.block_color);
-			if let Some(biome) = section.biomes.biome_at(section.y, coords)? {
+
+			let biome = section.biomes.biome_at(section.y, coords)?;
 			let (biome_index, _) = biome_list.insert_full(*biome);
 			*self.biome = NonZeroU16::new(
 				(biome_index + 1)
@@ -105,7 +106,6 @@ impl LayerEntry<'_> {
 					.expect("biome index not in range"),
 			);
 		}
-		}
 
 		if block_type.block_color.is(BlockFlag::Water) {
 			return Ok(false);

src/world/section.rs

@@ -208,7 +208,7 @@ impl Section for SectionV0<'_> {
 /// Trait for common functions of [BiomesV1_18] and [BiomesV0]
 pub trait Biomes: Debug {
 	/// Returns the [Biome] at a coordinate tuple inside the chunk
-	fn biome_at(&self, section: SectionY, coords: SectionBlockCoords) -> Result<Option<&Biome>>;
+	fn biome_at(&self, section: SectionY, coords: SectionBlockCoords) -> Result<&Biome>;
 }
 
 /// Minecraft v1.18+ section biome data
@@ -226,7 +226,7 @@ pub struct BiomesV1_18<'a> {
 	/// to whole i64 values.
 	biomes: Option<&'a [i64]>,
 	/// Biome palette indexed by entries encoded in *biomes*
-	palette: Vec<Option<&'a Biome>>,
+	palette: Vec<&'a Biome>,
 	/// Number of bits used for each entry in *biomes*
 	bits: u8,
 }
@@ -253,12 +253,11 @@ impl<'a> BiomesV1_18<'a> {
 		let palette_types = palette
 			.iter()
 			.map(|entry| {
-				let biome_type = biome_types.get(entry);
-				if biome_type.is_none() {
+				biome_types.get(entry).unwrap_or_else(|| {
 					debug!("Unknown biome type: {}", entry);
 					has_unknown = true;
-				}
-				biome_type
+					biome_types.get_fallback()
+				})
 			})
 			.collect();
 
@@ -295,7 +294,7 @@ impl<'a> BiomesV1_18<'a> {
 }
 
 impl Biomes for BiomesV1_18<'_> {
-	fn biome_at(&self, _section: SectionY, coords: SectionBlockCoords) -> Result<Option<&Biome>> {
+	fn biome_at(&self, _section: SectionY, coords: SectionBlockCoords) -> Result<&Biome> {
 		let index = self.palette_index_at(coords);
 		Ok(*self
 			.palette
@@ -350,7 +349,7 @@ impl<'a> BiomesV0<'a> {
 }
 
 impl Biomes for BiomesV0<'_> {
-	fn biome_at(&self, section: SectionY, coords: SectionBlockCoords) -> Result<Option<&Biome>> {
+	fn biome_at(&self, section: SectionY, coords: SectionBlockCoords) -> Result<&Biome> {
 		let id = match self.data {
 			BiomesV0Data::IntArrayV15(data) => {
 				let LayerBlockCoords { x, z } = coords.xz;
@@ -370,7 +369,10 @@ impl Biomes for BiomesV0<'_> {
 			}
 			BiomesV0Data::ByteArray(data) => data[coords.xz.offset()] as u8,
 		};
-		Ok(self.biome_types.get_legacy(id))
+		Ok(self
+			.biome_types
+			.get_legacy(id)
+			.unwrap_or(self.biome_types.get_fallback()))
 	}
 }