Add test for negative dash offset

vello_tests/tests/regression.rs

@@ -7,7 +7,7 @@ use scenes::ImageCache;
 use scenes::SimpleText;
 use vello::{
     AaConfig, Scene,
-    kurbo::{Affine, Rect, RoundedRect, Stroke},
+    kurbo::{Affine, Point, Rect, RoundedRect, Size, Stroke},
     peniko::{Extend, ImageQuality, color::palette},
 };
 use vello_tests::{TestParams, smoke_snapshot_test_sync, snapshot_test_sync};
@@ -89,3 +89,26 @@ fn text_stroke_width_zero() {
         .unwrap()
         .assert_mean_less_than(0.001);
 }
+
+/// Test for <https://github.com/linebender/vello/issues/1066>
+#[test]
+fn test_negative_dash_offset() {
+    let mut scene = Scene::new();
+    let stroke = Stroke::new(1.0).with_dashes(-30., [4., 2.]);
+    scene.stroke(
+        &stroke,
+        Affine::IDENTITY,
+        palette::css::BLUE,
+        None,
+        &Rect::from_origin_size(Point::new(1., 1.), Size::new(28., 28.)),
+    );
+    let mut params = TestParams::new("negative_dash_offset", 30, 30);
+    params.anti_aliasing = AaConfig::Area;
+    smoke_snapshot_test_sync(scene, &params)
+        .unwrap()
+        .assert_mean_less_than(if cfg!(target_os = "macos") {
+            0.005
+        } else {
+            0.001
+        });
+}