Adapt hack for tolerance of stroke expansion

sparse_strips/vello_common/src/flatten.rs

@@ -134,7 +134,11 @@ pub fn stroke(
     flatten_ctx: &mut FlattenCtx,
 ) {
     // TODO: Temporary hack to ensure that strokes are scaled properly by the transform.
-    let tolerance = TOL / affine.as_coeffs()[0].abs().max(affine.as_coeffs()[3].abs());
+    let tolerance = TOL
+        / affine.as_coeffs()[0]
+            .abs()
+            .max(affine.as_coeffs()[3].abs())
+            .max(1.);
 
     let expanded = expand_stroke(path, style, tolerance);
     fill(level, &expanded, affine, line_buf, flatten_ctx);

sparse_strips/vello_sparse_tests/tests/basic.rs

@@ -414,3 +414,23 @@ fn no_anti_aliasing_clip_path(ctx: &mut impl Renderer) {
     ctx.fill_rect(&rect);
     ctx.pop_layer();
 }
+
+#[vello_test(diff_pixels = 1)]
+fn stroke_scaled(ctx: &mut impl Renderer) {
+    let mut path = BezPath::new();
+    path.move_to((0.0, 0.0));
+    path.curve_to((0.25, 1.0), (0.75, 1.0), (1.0, 0.0));
+
+    // This path should be more or less completely covered.
+    let mut stroke = Stroke::new(10.0);
+    ctx.set_transform(Affine::IDENTITY);
+    ctx.set_stroke(stroke);
+    ctx.set_paint(RED);
+    ctx.stroke_path(&(Affine::scale(100.0) * path.clone()));
+
+    stroke = Stroke::new(0.1);
+    ctx.set_transform(Affine::scale(100.0));
+    ctx.set_stroke(stroke);
+    ctx.set_paint(LIME);
+    ctx.stroke_path(&path);
+}