Fix world pos to tile pos calculation for negative values

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);
+}