When hinting glyphs, round y-offsets to integers

sparse_strips/vello_common/src/glyph.rs

@@ -149,11 +149,18 @@ impl<'a, T: GlyphRenderer + 'a> GlyphRunBuilder<'a, T> {
                 local_transform *= glyph_transform;
             }
 
+            // When hinting, ensure the y-offset is integer. The x-offset doesn't matter, as we
+            // perform vertical-only hinting.
+            let mut total_transform = (transform * local_transform).as_coeffs();
+            if hinting_instance.is_some() {
+                total_transform[5] = total_transform[5].round();
+            }
+
             render_glyph(
                 self.renderer,
                 PreparedGlyph::Outline(OutlineGlyph {
                     path: &path.0,
-                    transform: transform * local_transform,
+                    transform: Affine::new(total_transform),
                 }),
             );
         }