diff --git a/src/game.rs b/src/game.rs
index ad1e6f2..906643c 100644
--- a/src/game.rs
+++ b/src/game.rs
@@ -25,8 +25,8 @@ impl GameState {
 }
 
 fn for_each_tile(camera_offset: WorldPos, mut f: impl FnMut(TilePos, ScreenPos)) {
-    for y in (0..NATIVE_RESOLUTION.h).step_by(32) {
-        for x in (0..NATIVE_RESOLUTION.w).step_by(32) {
+    for y in (-32..NATIVE_RESOLUTION.h + 32).step_by(32) {
+        for x in (-32..NATIVE_RESOLUTION.w + 32).step_by(32) {
             f(
                 TilePos {
                     x: (camera_offset.x + x as i32) / 32,
diff --git a/src/world.rs b/src/world.rs
index 0601c7c..7682ee8 100644
--- a/src/world.rs
+++ b/src/world.rs
@@ -3,7 +3,7 @@ use rand::{thread_rng, Rng};
 
 type ChunkPosScalar = i16;
 
-#[derive(Hash, PartialEq, Eq)]
+#[derive(Hash, PartialEq, Eq, Debug, Clone, Copy)]
 struct ChunkPos {
     x: ChunkPosScalar,
     y: ChunkPosScalar,
@@ -38,6 +38,7 @@ pub struct TilePos {
     pub y: TilePosScalar,
 }
 
+#[derive(Debug, PartialEq, Eq)]
 pub struct ChunkLocalTilePos {
     pub x: ChunkLocalTilePosScalar,
     pub y: ChunkLocalTilePosScalar,
@@ -49,22 +50,59 @@ impl TilePos {
     fn to_chunk_and_local(&self) -> (ChunkPos, ChunkLocalTilePos) {
         // 0,0 is chunk (0, 0)
         // -1, -1 is chunk (-1, -1)
-        let chk = ChunkPos {
+        // For negative offsets, local offset starts from `CHUNK_EXTENT`
+        let mut chk = ChunkPos {
             x: (self.x / CHUNK_EXTENT as i32) as i16,
             y: (self.y / CHUNK_EXTENT as i32) as i16,
         };
+        if self.x.is_negative() {
+            chk.x -= 1;
+        }
+        if self.y.is_negative() {
+            chk.y -= 1;
+        }
         let local = ChunkLocalTilePos {
-            x: (self.x % CHUNK_EXTENT as i32) as i16,
-            y: (self.y % CHUNK_EXTENT as i32) as i16,
+            x: if chk.x.is_negative() {
+                ((CHUNK_EXTENT as i32 + self.x) % CHUNK_EXTENT as i32) as i16
+            } else {
+                (self.x % CHUNK_EXTENT as i32) as i16
+            },
+            y: if chk.y.is_negative() {
+                ((CHUNK_EXTENT as i32 + self.y) % CHUNK_EXTENT as i32) as i16
+            } else {
+                (self.y % CHUNK_EXTENT as i32) as i16
+            },
         };
         (chk, local)
     }
 }
 
-// Need to support at least 8 million tiles long
+#[test]
+fn test_to_chunk_and_local() {
+    assert_eq!(
+        TilePos { x: 0, y: 0 }.to_chunk_and_local(),
+        (ChunkPos { x: 0, y: 0 }, ChunkLocalTilePos { x: 0, y: 0 })
+    );
+    assert_eq!(
+        TilePos { x: 1, y: 1 }.to_chunk_and_local(),
+        (ChunkPos { x: 0, y: 0 }, ChunkLocalTilePos { x: 1, y: 1 })
+    );
+    assert_eq!(
+        TilePos { x: -1, y: -1 }.to_chunk_and_local(),
+        (
+            ChunkPos { x: -1, y: -1 },
+            ChunkLocalTilePos {
+                x: CHUNK_EXTENT as i16 - 1,
+                y: CHUNK_EXTENT as i16 - 1
+            }
+        )
+    );
+}
+
+// Need to support at least 4 million tiles long
 type TilePosScalar = i32;
 
-const CHUNK_EXTENT: u16 = 256;
+const CHUNK_EXTENT: u16 = 128;
 const CHUNK_N_TILES: usize = CHUNK_EXTENT as usize * CHUNK_EXTENT as usize;
 
 type ChunkTiles = [Tile; CHUNK_N_TILES];