Gradients: an outlined stroke leaves dither behind, and paint.setStroke refuses it

Review follow-up (CodeRabbit): paint.setStroke kept `dither: true` from its
gradient, and a stroke can hold dither anyway (swapped from a fill). Outline
Stroke and appearance expansion copied the stroke's paint into the outline's
fill, which then drew dithered although the stroke never did. The outline's
fill now goes without dither (Paint::stroke_as_fill), and paint.setStroke
refuses a gradient with `dither: true`, as paint.editGradient does.

crates/color/src/lib.rs

@@ -378,6 +378,18 @@ impl Paint {
             _ => None,
         }
     }
+    /// This stroke paint as the fill of the stroke's outline, so the outline looks as the stroke
+    /// did: without dither, which strokes ignore ([`GradientPaint::draws_as_pixels`]).
+    pub fn stroke_as_fill(&self) -> Paint {
+        match self {
+            Paint::Gradient(g) if g.gradient.dither => {
+                let mut g = g.clone();
+                g.gradient.dither = false;
+                Paint::Gradient(g)
+            }
+            p => p.clone(),
+        }
+    }
     /// The Registration colour: 100% of every ink, linked to [`swatch::REGISTRATION`].
     pub fn registration() -> Self {
         Paint::Solid { color: Color::cmyk(1.0, 1.0, 1.0, 1.0), swatch: Some(swatch::REGISTRATION.into()), tint: 1.0 }

crates/effects/src/bake.rs

@@ -565,7 +565,7 @@ pub fn bake_appearance(n: &Node) -> Option<Node> {
                     }
                     None => {
                         let effects = st.effects.clone();
-                        let fill = FillLayer { opacity: st.opacity, blend: st.blend, effects, ..FillLayer::new(st.paint.clone()) };
+                        let fill = FillLayer { opacity: st.opacity, blend: st.blend, effects, ..FillLayer::new(st.paint.stroke_as_fill()) };
                         piece(outline, FillRule::NonZero, AppearanceItem::Fill(fill))
                     }
                 }
@@ -673,6 +673,22 @@ mod tests {
         assert_eq!(f.effects.iter().map(|e| e.id.as_str()).collect::<Vec<_>>(), ["stylize.dropShadow"]);
     }
 
+    #[test]
+    fn a_baked_stroke_leaves_dither_behind() {
+        // Strokes ignore dither, so the filled outline goes without it and looks as the stroke did.
+        let mut n = Node::path(NodeId(50), shapes::rectangle(Rect::new(0.0, 0.0, 100.0, 100.0)), Appearance::default_art());
+        if let AppearanceItem::Stroke(s) = &mut n.appearance.items[1] {
+            let mut g = vectorcraft_color::GradientPaint::new(Default::default());
+            g.gradient.dither = true;
+            s.paint = Paint::Gradient(Box::new(g));
+        }
+        let m = bake_appearance(&n).unwrap();
+        let ch = m.children().unwrap();
+        let Some(AppearanceItem::Fill(f)) = ch[1].appearance.items.first() else { panic!("the outline is filled") };
+        let Paint::Gradient(g) = &f.paint else { panic!("a gradient fill") };
+        assert!(!g.gradient.dither);
+    }
+
     #[test]
     fn a_baked_stroke_with_a_gradient_along_it_becomes_meshes_clipped_to_its_outline() {
         let mut n = Node::path(NodeId(50), shapes::rectangle(Rect::new(0.0, 0.0, 100.0, 100.0)), Appearance::default_art());

crates/engine/src/cmd/paint.rs

@@ -403,6 +403,10 @@ fn set_paint(s: &mut Session, p: &Value, fill: bool) -> Result<Value> {
     }
     check_keep_model(p, cmd)?;
     let paint = paint_from(s, p)?.ok_or_else(|| bad(cmd, "give color, none, swatch or gradient"))?;
+    // As `paint.editGradient`: a `dither` given applies to gradient fills only.
+    if !fill && matches!(&paint, Paint::Gradient(g) if g.gradient.dither) && p.get("swatch").is_none() {
+        return Err(bad(cmd, "`dither` applies to gradient fills (paint.setFill)"));
+    }
     apply_paint(s, p, paint, fill)
 }
 

crates/engine/src/cmd/pathops.rs

@@ -635,7 +635,7 @@ pub(crate) fn outlined_stroke(
         blend: st.blend,
         effects: st.effects.clone(),
         overprint: st.overprint,
-        ..vectorcraft_doc::appearance::FillLayer::new(st.paint.clone())
+        ..vectorcraft_doc::appearance::FillLayer::new(st.paint.stroke_as_fill())
     };
     n.appearance = Appearance { items: vec![AppearanceItem::Fill(fill)], ..Default::default() }.into();
     Some(n)

crates/engine/src/tests_gradient.rs

@@ -440,7 +440,29 @@ fn dither_is_a_fill_gradient_option_that_saves_and_loads() {
     s.execute("paint.setStroke", &json!({"gradient": {}})).unwrap();
     let before = node(&s, id).appearance.clone();
     assert!(s.execute("paint.editGradient", &json!({"dither": true, "stroke": true})).is_err());
+    assert!(s.execute("paint.setStroke", &json!({"gradient": {"dither": true}})).is_err());
     assert!(s.execute("paint.editGradient", &json!({"dither": "yes"})).is_err());
     assert!(s.execute("paint.setFill", &json!({"gradient": {"dither": 1}})).is_err());
     assert_eq!(node(&s, id).appearance, before);
 }
+
+/// A stroke ignores dither, so one that holds it anyway (swapped from a fill) outlines to a fill
+/// without it: Outline Stroke keeps the look.
+#[test]
+fn an_outlined_stroke_leaves_dither_behind() {
+    let mut s = session();
+    let id = rect(&mut s, 0.0, 0.0, 100.0, 100.0);
+    s.execute("paint.setStroke", &json!({"gradient": {}})).unwrap();
+    s.execute("paint.setFill", &json!({"gradient": {"dither": true}})).unwrap();
+    s.execute("paint.swap", &json!({})).unwrap();
+    let Paint::Gradient(st) = node(&s, id).appearance.stroke_paint() else { panic!("a gradient stroke") };
+    assert!(st.gradient.dither, "the swapped stroke keeps the option");
+    s.execute("object.path.outlineStroke", &json!({})).unwrap();
+    let mut fills = vec![];
+    s.doc().unwrap().doc.walk(|n| {
+        if let Paint::Gradient(g) = n.appearance.fill_paint() {
+            fills.push(g.gradient.dither);
+        }
+    });
+    assert_eq!(fills, [false, false], "the fill and the outline, neither dithered");
+}

crates/ui-egui/src/i18n/bg.tsv

@@ -5386,4 +5386,5 @@ axis	Y Axis	Y ос
 	Dither	Дитъринг
 	Fine noise hides banding in the gradient fill	Фин шум скрива ивиците в градиентната запълка
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` се прилага към градиентни запълки (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` се прилага към градиентни запълки (paint.setFill)
 @msg	`dither` must be true or false	`dither` трябва да бъде true или false

crates/ui-egui/src/i18n/cs.tsv

@@ -5431,4 +5431,5 @@ axis	Y Axis	osa Y
 	Dither	Rozptýlení
 	Fine noise hides banding in the gradient fill	Jemný šum skryje pruhy ve výplni přechodem
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` platí pro výplně přechodem (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` platí pro výplně přechodem (paint.setFill)
 @msg	`dither` must be true or false	`dither` musí být true nebo false

crates/ui-egui/src/i18n/da.tsv

@@ -5402,4 +5402,5 @@ axis	Y Axis	Y-akse
 	Dither	Dither
 	Fine noise hides banding in the gradient fill	Fin støj skjuler striber i gradientfyldet
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` gælder for gradientfyld (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` gælder for gradientfyld (paint.setFill)
 @msg	`dither` must be true or false	`dither` skal være true eller false

crates/ui-egui/src/i18n/de.tsv

@@ -5013,4 +5013,5 @@ axis	Y Axis	Y-Achse
 	Dither	Dithering
 	Fine noise hides banding in the gradient fill	Feines Rauschen verbirgt Streifen in der Verlaufsfläche
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` gilt für Verlaufsflächen (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` gilt für Verlaufsflächen (paint.setFill)
 @msg	`dither` must be true or false	`dither` muss true oder false sein

crates/ui-egui/src/i18n/el.tsv

@@ -5383,4 +5383,5 @@ axis	Y Axis	Άξονας Y
 	Dither	Πρόσθεση θορύβου
 	Fine noise hides banding in the gradient fill	Ο λεπτός θόρυβος κρύβει τις λωρίδες στο γέμισμα ντεγκραντέ
 @msg	`dither` applies to gradient fills (stroke: false)	Το `dither` ισχύει για γεμίσματα ντεγκραντέ (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	Το `dither` ισχύει για γεμίσματα ντεγκραντέ (paint.setFill)
 @msg	`dither` must be true or false	Το `dither` πρέπει να είναι true ή false

crates/ui-egui/src/i18n/es.tsv

@@ -5373,4 +5373,5 @@ axis	Y Axis	Eje Y
 	Dither	Tramado
 	Fine noise hides banding in the gradient fill	Un ruido fino oculta las bandas del relleno de degradado
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` se aplica a rellenos de degradado (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` se aplica a rellenos de degradado (paint.setFill)
 @msg	`dither` must be true or false	`dither` debe ser true o false

crates/ui-egui/src/i18n/fi.tsv

@@ -5462,4 +5462,5 @@ axis	Y Axis	Y-akseli
 	Dither	Rasterointi
 	Fine noise hides banding in the gradient fill	Hieno kohina piilottaa raidat liukuväritäytöstä
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` koskee liukuväritäyttöjä (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` koskee liukuväritäyttöjä (paint.setFill)
 @msg	`dither` must be true or false	`dither` on oltava true tai false

crates/ui-egui/src/i18n/fr.tsv

@@ -5430,4 +5430,5 @@ axis	Y Axis	Axe Y
 	Dither	Simulation
 	Fine noise hides banding in the gradient fill	Un bruit fin masque les bandes du fond en dégradé
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` s’applique aux fonds en dégradé (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` s’applique aux fonds en dégradé (paint.setFill)
 @msg	`dither` must be true or false	`dither` doit valoir true ou false

crates/ui-egui/src/i18n/hu.tsv

@@ -5417,4 +5417,5 @@ axis	Y Axis	Y tengely
 	Dither	Árnyalatkeverés
 	Fine noise hides banding in the gradient fill	A finom zaj elrejti a sávokat a színátmenetes kitöltésben
 @msg	`dither` applies to gradient fills (stroke: false)	A `dither` színátmenetes kitöltésekre vonatkozik (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	A `dither` színátmenetes kitöltésekre vonatkozik (paint.setFill)
 @msg	`dither` must be true or false	`dither`: true vagy false kell

crates/ui-egui/src/i18n/id.tsv

@@ -5402,4 +5402,5 @@ axis	Y Axis	Sumbu Y
 	Dither	Dither
 	Fine noise hides banding in the gradient fill	Derau halus menyembunyikan pita warna pada isian gradien
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` berlaku untuk isian gradien (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` berlaku untuk isian gradien (paint.setFill)
 @msg	`dither` must be true or false	`dither` harus true atau false

crates/ui-egui/src/i18n/it.tsv

@@ -5047,4 +5047,5 @@ axis	Y Axis	Asse Y
 	Dither	Dithering
 	Fine noise hides banding in the gradient fill	Un rumore fine nasconde le bande nel riempimento sfumato
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` si applica ai riempimenti sfumati (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` si applica ai riempimenti sfumati (paint.setFill)
 @msg	`dither` must be true or false	`dither` deve essere true o false

crates/ui-egui/src/i18n/ja.tsv

@@ -5109,4 +5109,5 @@ axis	Y Axis	Y 軸
 	Dither	ディザ
 	Fine noise hides banding in the gradient fill	細かいノイズでグラデーションの塗りの縞を目立たなくします
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` はグラデーションの塗りに適用されます (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` はグラデーションの塗りに適用されます (paint.setFill)
 @msg	`dither` must be true or false	`dither` には true または false を指定してください

crates/ui-egui/src/i18n/ka.tsv

@@ -5347,4 +5347,5 @@ axis	Y Axis	Y ღერძი
 	Dither	დიზერინგი
 	Fine noise hides banding in the gradient fill	წვრილი ხმაური მალავს ზოლებს გრადიენტულ შევსებაში
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` ვრცელდება გრადიენტულ შევსებებზე (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` ვრცელდება გრადიენტულ შევსებებზე (paint.setFill)
 @msg	`dither` must be true or false	`dither` უნდა იყოს true ან false

crates/ui-egui/src/i18n/ko.tsv

@@ -5010,4 +5010,5 @@ axis	Y Axis	Y축
 	Dither	디더
 	Fine noise hides banding in the gradient fill	미세한 노이즈로 그레이디언트 칠의 띠를 감춥니다
 @msg	`dither` applies to gradient fills (stroke: false)	`dither`는 그레이디언트 칠에 적용됩니다 (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither`는 그레이디언트 칠에 적용됩니다 (paint.setFill)
 @msg	`dither` must be true or false	`dither`은(는) true 또는 false여야 합니다

crates/ui-egui/src/i18n/nl.tsv

@@ -5445,4 +5445,5 @@ axis	Y Axis	Y-as
 	Dither	Dither
 	Fine noise hides banding in the gradient fill	Fijne ruis verbergt banden in de verloopvulling
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` geldt voor verloopvullingen (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` geldt voor verloopvullingen (paint.setFill)
 @msg	`dither` must be true or false	`dither` moet true of false zijn

crates/ui-egui/src/i18n/pl.tsv

@@ -5283,4 +5283,5 @@ axis	Y Axis	Oś Y
 	Dither	Rozpraszanie
 	Fine noise hides banding in the gradient fill	Drobny szum ukrywa pasy w wypełnieniu gradientem
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` dotyczy wypełnień gradientem (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` dotyczy wypełnień gradientem (paint.setFill)
 @msg	`dither` must be true or false	`dither` musi mieć wartość true lub false

crates/ui-egui/src/i18n/pt-br.tsv

@@ -5348,4 +5348,5 @@ axis	Y Axis	Eixo Y
 	Dither	Dither
 	Fine noise hides banding in the gradient fill	Um ruído fino esconde as faixas do preenchimento em gradiente
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` se aplica a preenchimentos em gradiente (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` se aplica a preenchimentos em gradiente (paint.setFill)
 @msg	`dither` must be true or false	`dither` deve ser true ou false

crates/ui-egui/src/i18n/ru.tsv

@@ -5043,4 +5043,5 @@ axis	Y Axis	Ось Y
 	Dither	Дизеринг
 	Fine noise hides banding in the gradient fill	Мелкий шум скрывает полосы в градиентной заливке
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` применяется к градиентным заливкам (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` применяется к градиентным заливкам (paint.setFill)
 @msg	`dither` must be true or false	`dither` должно быть true или false

crates/ui-egui/src/i18n/sv.tsv

@@ -5387,4 +5387,5 @@ axis	Y Axis	Y-axel
 	Dither	Dithering
 	Fine noise hides banding in the gradient fill	Fint brus döljer bandningen i övertoningsfyllningen
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` gäller övertoningsfyllningar (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` gäller övertoningsfyllningar (paint.setFill)
 @msg	`dither` must be true or false	`dither` måste vara true eller false

crates/ui-egui/src/i18n/tr.tsv

@@ -5395,4 +5395,5 @@ axis	Y Axis	Y ekseni
 	Dither	Titreme
 	Fine noise hides banding in the gradient fill	İnce gürültü, degrade dolgudaki bantları gizler
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` degrade dolgulara uygulanır (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` degrade dolgulara uygulanır (paint.setFill)
 @msg	`dither` must be true or false	"dither" doğru veya yanlış olmalıdır

crates/ui-egui/src/i18n/uk.tsv

@@ -5027,4 +5027,5 @@ axis	Y Axis	Вісь Y
 	Dither	Дизеринг
 	Fine noise hides banding in the gradient fill	Дрібний шум приховує смуги в градієнтній заливці
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` застосовується до градієнтних заливок (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` застосовується до градієнтних заливок (paint.setFill)
 @msg	`dither` must be true or false	`dither` має бути true або false

crates/ui-egui/src/i18n/vi.tsv

@@ -5027,4 +5027,5 @@ axis	Y Axis	Trục Y
 	Dither	Dither
 	Fine noise hides banding in the gradient fill	Nhiễu mịn che dải màu trong vùng tô chuyển sắc
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` áp dụng cho vùng tô chuyển sắc (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` áp dụng cho vùng tô chuyển sắc (paint.setFill)
 @msg	`dither` must be true or false	`dither` phải là true hoặc false

crates/ui-egui/src/i18n/zh-hans.tsv

@@ -5271,4 +5271,5 @@ axis	Y Axis	Y 轴
 	Dither	仿色
 	Fine noise hides banding in the gradient fill	细微杂色可隐藏渐变填色中的色带
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` 适用于渐变填色 (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` 适用于渐变填色 (paint.setFill)
 @msg	`dither` must be true or false	`dither` 必须是 true 或 false

crates/ui-egui/src/i18n/zh-hant.tsv

@@ -5066,4 +5066,5 @@ axis	Y Axis	Y 軸
 	Dither	仿色
 	Fine noise hides banding in the gradient fill	細微雜色可隱藏漸層填色中的色帶
 @msg	`dither` applies to gradient fills (stroke: false)	`dither` 適用於漸層填色 (stroke: false)
+@msg	`dither` applies to gradient fills (paint.setFill)	`dither` 適用於漸層填色 (paint.setFill)
 @msg	`dither` must be true or false	`dither` 必須是 true 或 false