Store `x` and `y` in `Region` as u16

sparse_strips/vello_cpu/src/fine/mod.rs

diff --git a/sparse_strips/vello_cpu/src/fine/mod.rs b/sparse_strips/vello_cpu/src/fine/mod.rs
index 25294bc..05f6bf8 100644
--- a/sparse_strips/vello_cpu/src/fine/mod.rs
+++ b/sparse_strips/vello_cpu/src/fine/mod.rs
@@ -91,13 +91,13 @@
     pub fn pack(&mut self, region: &mut Region<'_>) {
         let blend_buf = self.blend_buf.last().unwrap();
 
-        for y in 0..Tile::HEIGHT as usize {
+        for y in 0..Tile::HEIGHT {
             for (x, pixel) in region
                 .row_mut(y)
                 .chunks_exact_mut(COLOR_COMPONENTS)
                 .enumerate()
             {
-                let idx = COLOR_COMPONENTS * (Tile::HEIGHT as usize * x + y);
+                let idx = COLOR_COMPONENTS * (usize::from(Tile::HEIGHT) * x + usize::from(y));
                 pixel.copy_from_slice(&F::to_rgba8(&blend_buf[idx..][..COLOR_COMPONENTS]));
             }
         }

sparse_strips/vello_cpu/src/region.rs

diff --git a/sparse_strips/vello_cpu/src/region.rs b/sparse_strips/vello_cpu/src/region.rs
index 9772ec3..6dd6cab 100644
--- a/sparse_strips/vello_cpu/src/region.rs
+++ b/sparse_strips/vello_cpu/src/region.rs
@@ -51,7 +51,11 @@
                     next_lines[h] = tail;
                 }
 
-                regions.push(Region::new(areas, x, y));
+                regions.push(Region::new(
+                    areas,
+                    u16::try_from(x).unwrap(),
+                    u16::try_from(y).unwrap(),
+                ));
             }
         }
 
@@ -73,25 +77,25 @@
 }
 
 /// A rectangular region containing the pixels from one wide tile.
-/// 
+///
 /// For wide tiles at the right/bottom edge, it might contain less pixels
 /// than the actual wide tile, if the pixmap width/height isn't a multiple of the
 /// tile width/height.
 #[derive(Default, Debug)]
 pub struct Region<'a> {
     /// The x coordinate of the wide tile this region covers.
-    pub(crate) x: usize,
+    pub(crate) x: u16,
     /// The y coordinate of the wide tile this region covers.
-    pub(crate) y: usize,
+    pub(crate) y: u16,
     areas: [&'a mut [u8]; Tile::HEIGHT as usize],
 }
 
 impl<'a> Region<'a> {
-    pub(crate) fn new(areas: [&'a mut [u8]; Tile::HEIGHT as usize], x: usize, y: usize) -> Self {
+    pub(crate) fn new(areas: [&'a mut [u8]; Tile::HEIGHT as usize], x: u16, y: u16) -> Self {
         Self { areas, x, y }
     }
 
-    pub(crate) fn row_mut(&mut self, y: usize) -> &mut [u8] {
-        self.areas[y]
+    pub(crate) fn row_mut(&mut self, y: u16) -> &mut [u8] {
+        self.areas[usize::from(y)]
     }
 }

sparse_strips/vello_cpu/src/render.rs

diff --git a/sparse_strips/vello_cpu/src/render.rs b/sparse_strips/vello_cpu/src/render.rs
index 812470e..943053c 100644
--- a/sparse_strips/vello_cpu/src/render.rs
+++ b/sparse_strips/vello_cpu/src/render.rs
@@ -340,8 +340,8 @@
                     .get_or(|| core::cell::RefCell::new(Fine::new()))
                     .borrow_mut();
 
-                let wtile = self.wide.get(x as u16, y as u16);
-                fine.set_coords(x as u16, y as u16);
+                let wtile = self.wide.get(x, y);
+                fine.set_coords(x, y);
 
                 fine.clear(F::extract_color(&wtile.bg));
                 for cmd in &wtile.cmds {