Properly center screen

src/math.rs

@@ -1,3 +1,5 @@
+use num_traits::Signed;
+
 use crate::world::{TilePos, TilePosScalar};
 
 pub type WorldPosScalar = u32;
@@ -50,6 +52,23 @@ pub fn wp_to_tp(wp: WorldPosScalar) -> TilePosScalar {
     (wp / TILE_SIZE as WorldPosScalar) as TilePosScalar
 }
 
+// Get the offset required to center an object of `xw` width inside an object of `yw` width.
+//
+// For example, let's say `xw` (+) is 10 and we want to center it inside `yw` (-), which is 20
+//
+// ++++++++++           (x uncentered)
+// -------------------- (y)
+//      ++++++++++      (x centered)
+//
+// In this case, we needed to add 5 to x to achieve centering.
+// This is the offset that this function calculates.
+//
+// We can calulate it by subtracting `xw` from `yw` (10), and dividing it by 2.
+pub fn center_offset<N: From<u8> + Copy + Signed>(xw: N, yw: N) -> N {
+    let diff = yw - xw;
+    diff / N::from(2)
+}
+
 #[test]
 fn test_wp_to_tp() {
     assert_eq!(wp_to_tp(0), 0);