world/layer: return None from top_layer() for empty chunks

Allow ignoring these chunks for the light map as well.

src/main.rs

@@ -98,7 +98,10 @@ impl<'a> RegionProcessor<'a> {
 	}
 
 	/// Processes a single chunk
-	fn process_chunk(&self, data: world::de::Chunk) -> Result<Box<world::layer::BlockInfoArray>> {
+	fn process_chunk(
+		&self,
+		data: world::de::Chunk,
+	) -> Result<Option<Box<world::layer::BlockInfoArray>>> {
 		let chunk = world::chunk::Chunk::new(&data, &self.block_types)?;
 		world::layer::top_layer(&chunk)
 	}
@@ -127,9 +130,12 @@ impl<'a> RegionProcessor<'a> {
 
 		minedmap::io::region::from_file(path)?.foreach_chunk(
 			|chunk_coords, data: world::de::Chunk| {
-				let processed_chunk = self
+				let Some(processed_chunk) = self
 					.process_chunk(data)
-					.with_context(|| format!("Failed to process chunk {:?}", chunk_coords))?;
+					.with_context(|| format!("Failed to process chunk {:?}", chunk_coords))?
+				else {
+					return Ok(());
+				};
 				processed_region[chunk_coords] = Some(processed_chunk);
 				Ok(())
 			},

src/world/chunk.rs

@@ -179,6 +179,15 @@ impl<'a> Chunk<'a> {
 		)
 	}
 
+	pub fn is_empty(&self) -> bool {
+		match self {
+			Chunk::V1_18 { section_map } => section_map.is_empty(),
+			Chunk::V1_13 { section_map, .. } => section_map.is_empty(),
+			Chunk::V0 { section_map, .. } => section_map.is_empty(),
+			Chunk::Empty => true,
+		}
+	}
+
 	/// Returns an interator over the chunk's sections and their Y coordinates
 	pub fn sections(&self) -> SectionIter {
 		use SectionIterInner::*;

src/world/layer.rs

@@ -91,9 +91,13 @@ pub type BlockInfoArray = LayerBlockArray<Option<BlockInfo>>;
 /// determined as the block that should be visible on the rendered
 /// map. For water blocks, the height of the first non-water block
 /// is additionally filled in as the water depth.
-pub fn top_layer(chunk: &Chunk) -> Result<Box<BlockInfoArray>> {
+pub fn top_layer(chunk: &Chunk) -> Result<Option<Box<BlockInfoArray>>> {
 	use BLOCKS_PER_CHUNK as N;
 
+	if chunk.is_empty() {
+		return Ok(None);
+	}
+
 	let mut done = 0;
 	let mut ret = Box::<BlockInfoArray>::default();
 
@@ -129,5 +133,5 @@ pub fn top_layer(chunk: &Chunk) -> Result<Box<BlockInfoArray>> {
 		}
 	}
 
-	Ok(ret)
+	Ok(Some(ret))
 }