minedmap/tile_renderer: keep HashSet of populated regions

Rather than attemping to read the file metadata, it's more elegant to
check whether a tile is supposed to be available first.

src/bin/minedmap/common.rs

@@ -12,7 +12,7 @@ use minedmap::{io::fs::FileMetaVersion, resource::Biome, types::*, world::layer}
 // Increase to force regeneration of all output files
 pub const FILE_META_VERSION: FileMetaVersion = FileMetaVersion(0);
 
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct TileCoords {
 	pub x: i32,
 	pub z: i32,

src/bin/minedmap/region_group.rs

@@ -16,25 +16,24 @@ pub struct RegionGroup<T> {
 }
 
 impl<T> RegionGroup<T> {
-	pub fn new<F>(f: F) -> Result<Self>
+	pub fn new<F>(f: F) -> Self
 	where
-		F: Fn(i8, i8) -> Result<T>,
+		F: Fn(i8, i8) -> Option<T>,
 	{
 		RegionGroup {
-			center: (0, 0),
+			center: f(0, 0).expect("Center element of RegionGroup must not be None"),
 			neighs: [
-				Some((-1, -1)),
-				Some((-1, 0)),
-				Some((-1, 1)),
-				Some((0, -1)),
+				f(-1, -1),
+				f(-1, 0),
+				f(-1, 1),
+				f(0, -1),
 				None,
-				Some((0, 1)),
-				Some((1, -1)),
-				Some((1, 0)),
-				Some((1, 1)),
+				f(0, 1),
+				f(1, -1),
+				f(1, 0),
+				f(1, 1),
 			],
 		}
-		.try_map(|(x, z)| f(x, z))
 	}
 
 	pub fn center(&self) -> &T {

src/bin/minedmap/tile_renderer.rs

@@ -51,6 +51,7 @@ pub struct TileRenderer<'a> {
 	config: &'a Config,
 	rt: &'a tokio::runtime::Runtime,
 	regions: &'a [TileCoords],
+	region_set: rustc_hash::FxHashSet<TileCoords>,
 	region_cache: Mutex<LruCache<PathBuf, Arc<OnceCell<RegionRef>>>>,
 }
 
@@ -63,10 +64,12 @@ impl<'a> TileRenderer<'a> {
 		let region_cache = Mutex::new(LruCache::new(
 			NonZeroUsize::new(6 + 6 * config.num_threads).unwrap(),
 		));
+		let region_set = regions.iter().copied().collect();
 		TileRenderer {
 			config,
 			rt,
 			regions,
+			region_set,
 			region_cache,
 		}
 	}
@@ -204,11 +207,13 @@ impl<'a> TileRenderer<'a> {
 
 	fn processed_sources(&self, coords: TileCoords) -> Result<(RegionGroup<PathBuf>, SystemTime)> {
 		let sources = RegionGroup::new(|x, z| {
-			self.processed_source(TileCoords {
+			Some(TileCoords {
 				x: coords.x + (x as i32),
 				z: coords.z + (z as i32),
 			})
+			.filter(|entry| self.region_set.contains(entry))
 		})
+		.try_map(|entry| self.processed_source(entry))
 		.with_context(|| format!("Region {:?} from previous step must exist", coords))?;
 
 		let max_timestamp = *sources