minedmap/tile_renderer: add coord_offset() helper

src/bin/minedmap/tile_renderer.rs

@@ -4,6 +4,7 @@ use std::{
 };
 
 use anyhow::{Context, Result};
+use num_integer::div_mod_floor;
 
 use minedmap::{
 	io::{fs, storage},
@@ -13,6 +14,29 @@ use minedmap::{
 
 use super::{common::*, region_group::RegionGroup};
 
+/// Offsets a chunk and block coordinate pair by a number of blocks
+///
+/// As the new coordinate may end up in a different region, a region offset
+/// is returned together with the new chunk and block coordinates.
+fn coord_offset<const AXIS: u8>(
+	chunk: ChunkCoord<AXIS>,
+	block: BlockCoord<AXIS>,
+	offset: i32,
+) -> (i8, ChunkCoord<AXIS>, BlockCoord<AXIS>) {
+	const CHUNKS: i32 = CHUNKS_PER_REGION as i32;
+	const BLOCKS: i32 = BLOCKS_PER_CHUNK as i32;
+	let coord = chunk.0 as i32 * BLOCKS + block.0 as i32 + offset;
+	let (region_chunk, block) = div_mod_floor(coord, BLOCKS);
+	let (region, chunk) = div_mod_floor(region_chunk, CHUNKS);
+	(
+		region
+			.try_into()
+			.expect("the region coordinate should be in the valid range"),
+		ChunkCoord::new(chunk),
+		BlockCoord::new(block),
+	)
+}
+
 pub struct TileRenderer<'a> {
 	config: &'a Config,
 }
@@ -147,3 +171,37 @@ impl<'a> TileRenderer<'a> {
 		Ok(())
 	}
 }
+
+#[cfg(test)]
+mod test {
+	use super::*;
+
+	#[test]
+	fn test_coord_offset() {
+		const CHUNKS: i32 = CHUNKS_PER_REGION as i32;
+		const BLOCKS: i32 = BLOCKS_PER_CHUNK as i32;
+
+		for chunk in ChunkX::iter() {
+			for block in BlockX::iter() {
+				assert_eq!(coord_offset(chunk, block, 0), (0, chunk, block));
+				assert_eq!(
+					coord_offset(chunk, block, -(CHUNKS * BLOCKS)),
+					(-1, chunk, block)
+				);
+				assert_eq!(
+					coord_offset(chunk, block, CHUNKS * BLOCKS),
+					(1, chunk, block)
+				);
+
+				for offset in -(CHUNKS * BLOCKS)..(CHUNKS * BLOCKS) {
+					let (region2, chunk2, block2) = coord_offset(chunk, block, offset);
+					assert!((-1..=1).contains(&region2));
+					let coord = chunk.0 as i32 * BLOCKS + block.0 as i32 + offset;
+					let coord2 =
+						((region2 as i32 * CHUNKS) + chunk2.0 as i32) * BLOCKS + block2.0 as i32;
+					assert_eq!(coord2, coord);
+				}
+			}
+		}
+	}
+}