Fix world pos to tile pos calculation for negative values

src/game.rs

@@ -2,7 +2,7 @@ use sfml::graphics::{Rect, RenderTarget, RenderWindow, Sprite, Transformable};
 
 use crate::{
     graphics::{ScreenPos, NATIVE_RESOLUTION},
-    math::WorldPos,
+    math::{wp_to_tp, WorldPos, WorldPosScalar},
     res::Res,
     world::{TilePos, World},
 };
@@ -28,8 +28,8 @@ fn for_each_tile(camera_offset: WorldPos, mut f: impl FnMut(TilePos, ScreenPos))
         for x in (-32..NATIVE_RESOLUTION.w + 32).step_by(32) {
             f(
                 TilePos {
-                    x: (camera_offset.x + x as i32) / 32,
-                    y: (camera_offset.y + y as i32) / 32,
+                    x: wp_to_tp(camera_offset.x + x as WorldPosScalar),
+                    y: wp_to_tp(camera_offset.y + y as WorldPosScalar),
                 },
                 ScreenPos {
                     x: (x as i32 - camera_offset.x % 32) as i16,

src/math.rs

@@ -1,4 +1,4 @@
-use crate::world::TilePos;
+use crate::world::{TilePos, TilePosScalar};
 
 pub type WorldPosScalar = i32;
 
@@ -8,13 +8,31 @@ pub struct WorldPos {
     pub y: WorldPosScalar,
 }
 
+pub const TILE_SIZE: u8 = 32;
+
 impl WorldPos {
     pub fn tile_pos(&self) -> TilePos {
         TilePos {
-            x: self.x / TILE_SIZE as i32,
-            y: self.y / TILE_SIZE as i32,
+            x: wp_to_tp(self.x),
+            y: wp_to_tp(self.y),
         }
     }
 }
 
-pub const TILE_SIZE: u8 = 32;
+pub fn wp_to_tp(wp: WorldPosScalar) -> TilePosScalar {
+    if wp.is_negative() {
+        (wp + 1) / TILE_SIZE as TilePosScalar - 1
+    } else {
+        wp / TILE_SIZE as TilePosScalar
+    }
+}
+
+#[test]
+fn test_wp_to_tp() {
+    assert_eq!(wp_to_tp(0), 0);
+    assert_eq!(wp_to_tp(1), 0);
+    assert_eq!(wp_to_tp(33), 1);
+    assert_eq!(wp_to_tp(-1), -1);
+    assert_eq!(wp_to_tp(-32), -1);
+    assert_eq!(wp_to_tp(-33), -2);
+}

src/world.rs

@@ -140,7 +140,7 @@ fn test_to_chunk_and_local() {
 }
 
 // Need to support at least 4 million tiles long
-type TilePosScalar = i32;
+pub type TilePosScalar = i32;
 
 const CHUNK_EXTENT: u16 = 128;
 const CHUNK_N_TILES: usize = CHUNK_EXTENT as usize * CHUNK_EXTENT as usize;