world/layer: avoid iproduct-based iterator in inner loop

iproduct iterators are fairly slow. As the iterator implementation is
now unused, it is removed as well.

src/types.rs

@@ -73,20 +73,6 @@ impl LayerBlockCoords {
 #[derive(Debug, Clone, Copy, Default, Serialize, Deserialize)]
 pub struct LayerBlockArray<T>(pub [[T; BLOCKS_PER_CHUNK]; BLOCKS_PER_CHUNK]);
 
-impl<T> LayerBlockArray<T> {
-	pub fn keys() -> impl Iterator<Item = LayerBlockCoords> + Clone + Debug {
-		iproduct!(BlockZ::iter(), BlockX::iter()).map(|(z, x)| LayerBlockCoords { x, z })
-	}
-
-	pub fn values(&self) -> impl Iterator<Item = &T> + Clone + Debug {
-		Self::keys().map(|k| &self[k])
-	}
-
-	pub fn iter(&self) -> impl Iterator<Item = (LayerBlockCoords, &T)> + Clone + Debug {
-		Self::keys().map(|k| (k, &self[k]))
-	}
-}
-
 impl<T> Index<LayerBlockCoords> for LayerBlockArray<T> {
 	type Output = T;
 

src/world/layer.rs

@@ -111,7 +111,10 @@ pub fn top_layer(chunk: &Chunk) -> Result<Option<LayerData>> {
 
 	for section in chunk.sections().rev() {
 		for y in BlockY::iter().rev() {
-			for xz in LayerBlockArray::<()>::keys() {
+			for z in BlockZ::iter() {
+				for x in BlockX::iter() {
+					let xz = LayerBlockCoords { x, z };
+
 					let mut entry = ret.entry(xz);
 					if entry.done() {
 						continue;
@@ -130,6 +133,7 @@ pub fn top_layer(chunk: &Chunk) -> Result<Option<LayerData>> {
 				}
 			}
 		}
+	}
 
 	Ok(Some(ret))
 }