Fix affine background matrix creation outside of the 1st quadrant (#714)

- [x] Changelog updated

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added `find_colour_index_16` and `find_colour_index_256` to the `VRamManager` to find where a colour is in a palette.
 
+### Fixed
+
+- Affine background center position didn't work outside of the upper left quadrant of the gba's screen.
+
 ## [0.20.2] - 2024/05/25
 
 ### Fixed

agb/examples/affine_background.rs

@@ -43,8 +43,8 @@ fn main(mut gba: agb::Gba) -> ! {
 
     loop {
         input.update();
-        scroll_x += input.x_tri() as i32;
-        scroll_y += input.y_tri() as i32;
+        scroll_x += input.x_tri() as i16;
+        scroll_y += input.y_tri() as i16;
 
         let scroll_pos = (scroll_x, scroll_y);
 

agb/src/display/affine.rs

@@ -298,11 +298,11 @@ impl AffineMatrixBackground {
         transform_origin: impl Into<Vector2D<Num<i32, 8>>>,
         scale: impl Into<Vector2D<Num<i32, 8>>>,
         rotation: Num<i32, 16>,
-        position: impl Into<Vector2D<Num<i32, 8>>>,
+        position: impl Into<Vector2D<i16>>,
     ) -> Self {
         crate::syscall::bg_affine_matrix(
             transform_origin.into(),
-            position.into().try_change_base::<i16, 8>().unwrap().floor(),
+            position.into(),
             scale.into().try_change_base().unwrap(),
             rotation.rem_euclid(1.into()).try_change_base().unwrap(),
         )