fix(ui): A tint keeps each object's swatch, and no stroke stays none

Changing the Tint in the Fill menu sent the first object's swatch with
it, so with several objects selected every fill became that swatch; and
a Stroke tint on a frame without a stroke gave it the default 1 pt black
stroke.

object.fill now takes a tint alone and keeps each object's swatch, and
object.stroke with only a tint leaves a [None] stroke alone; the menu
sends just the tint.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/object.rs

@@ -160,11 +160,31 @@ pub fn specs() -> Vec<CommandSpec> {
                 )
             }
         ),
-        cmd!("object.fill", "Fill", [], None, "{swatch, tint?: 0..1, ids?}", has_selection, |s, p| {
-            let sw = str_param(p, "swatch").ok_or_else(|| bad("object.fill", "missing swatch"))?.to_string();
-            let tint = f64_or(p, "tint", 1.0) as f32;
-            set_flag(s, p, move |i| i.fill = Fill { swatch: sw.clone(), tint, ..i.fill.clone() }, false)
-        }),
+        cmd!(
+            "object.fill",
+            "Fill",
+            [],
+            None,
+            "{swatch?, tint?: 0..1, ids?} — a swatch (tint 100% unless given), or a tint alone that keeps each object's swatch",
+            has_selection,
+            |s, p| {
+                let sw = str_param(p, "swatch").map(str::to_string);
+                let tint = p.get("tint").and_then(Value::as_f64).filter(|t| t.is_finite()).map(|t| t.clamp(0.0, 1.0) as f32);
+                if sw.is_none() && tint.is_none() {
+                    return Err(bad("object.fill", "missing swatch"));
+                }
+                set_flag(
+                    s,
+                    p,
+                    move |i| {
+                        let swatch = sw.clone().unwrap_or_else(|| i.fill.swatch.clone());
+                        let tint = tint.unwrap_or(if sw.is_some() { 1.0 } else { i.fill.tint });
+                        i.fill = Fill { swatch, tint, ..i.fill.clone() };
+                    },
+                    false,
+                )
+            }
+        ),
         cmd!(
             "object.stroke",
             "Stroke",
@@ -174,10 +194,15 @@ pub fn specs() -> Vec<CommandSpec> {
             has_selection,
             |s, p| {
                 let p2 = p.clone();
+                // A tint alone changes no stroke into one (it would become the default 1 pt black).
+                let tint_only = p.as_object().is_some_and(|o| o.keys().all(|k| k == "tint" || k == "ids"));
                 set_flag(
                     s,
                     p,
                     move |i| {
+                        if tint_only && i.stroke.is_none() {
+                            return;
+                        }
                         let mut st = if i.stroke.is_none() && p2.get("swatch").is_none() { Stroke::default() } else { i.stroke.clone() };
                         if let Some(v) = p2.get("swatch").and_then(Value::as_str) {
                             st.swatch = v.into();
@@ -2714,3 +2739,31 @@ mod blend_mode_tests {
         assert_eq!(it.opacity, 1.0);
     }
 }
+
+#[cfg(test)]
+mod tint_alone_tests {
+    use serde_json::json;
+
+    #[test]
+    fn a_tint_alone_keeps_each_swatch_and_leaves_no_stroke_alone() {
+        let mut s = crate::Session::new();
+        s.execute("file.new", &json!({})).unwrap();
+        let a = s.execute("frame.create", &json!({"rect": [0, 0, 50, 50]})).unwrap()["id"].as_u64().unwrap();
+        let b = s.execute("frame.create", &json!({"rect": [60, 0, 110, 50]})).unwrap()["id"].as_u64().unwrap();
+        s.execute("object.fill", &json!({"swatch": "[Black]", "ids": [a]})).unwrap();
+        s.execute("object.fill", &json!({"swatch": "C=100 M=0 Y=0 K=0", "ids": [b]})).unwrap();
+        s.execute("object.stroke", &json!({"swatch": "[None]", "ids": [a, b]})).unwrap();
+        // Fill tint on both: each keeps its swatch.
+        s.execute("object.fill", &json!({"tint": 0.25, "ids": [a, b]})).unwrap();
+        let item = |s: &crate::Session, id: u64| s.doc().unwrap().doc.item(designcraft_doc::ItemId(id)).unwrap().clone();
+        assert_eq!((item(&s, a).fill.swatch.as_str(), item(&s, a).fill.tint), ("[Black]", 0.25));
+        assert_eq!((item(&s, b).fill.swatch.as_str(), item(&s, b).fill.tint), ("C=100 M=0 Y=0 K=0", 0.25));
+        // A swatch alone is 100%.
+        s.execute("object.fill", &json!({"swatch": "[Paper]", "ids": [a]})).unwrap();
+        assert_eq!(item(&s, a).fill.tint, 1.0);
+        // A stroke tint on no stroke: still no stroke.
+        s.execute("object.stroke", &json!({"tint": 0.5, "ids": [a]})).unwrap();
+        assert!(item(&s, a).stroke.is_none(), "{:?}", item(&s, a).stroke);
+        assert!(s.execute("object.fill", &json!({"ids": [a]})).is_err(), "neither swatch nor tint");
+    }
+}

crates/ui-egui/src/panels/properties.rs

@@ -736,9 +736,6 @@ fn swatch_menu(
             if let Some(v) = p.remove(tint_key) {
                 p.insert("tint".into(), v);
             }
-            if !stroke && !p.contains_key("swatch") {
-                p.insert("swatch".into(), json!(cur));
-            }
             let _ = app.run(if stroke { "object.stroke" } else { "object.fill" }, Value::Object(p));
         }
     };
@@ -2316,6 +2313,34 @@ mod tests {
         assert_eq!((fill.swatch.as_str(), fill.tint), (CYAN, 0.25), "the tint, on the same swatch");
     }
 
+    #[test]
+    fn a_tint_on_several_objects_keeps_each_ones_swatch() {
+        let mut app = DesignApp::new(designcraft_engine::Session::new(), crate::Services::default());
+        app.run("file.new", json!({})).unwrap();
+        let a = app.run("frame.create", json!({"rect": [72, 72, 200, 200]})).unwrap()["id"].as_u64().unwrap();
+        let b = app.run("frame.create", json!({"rect": [220, 72, 300, 200]})).unwrap()["id"].as_u64().unwrap();
+        app.run("object.fill", json!({"swatch": CYAN, "ids": [a]})).unwrap();
+        app.run("object.fill", json!({"swatch": "[Black]", "ids": [b]})).unwrap();
+        app.run("selection.set", json!({"ids": [a, b]})).unwrap();
+        let mut h = panel(app);
+        h.get_by_label("Fill swatch").click();
+        h.run_steps(3);
+        let row = h.get_by_label("Tint:").rect();
+        h.query_all_by(|n| n.role() == egui::accesskit::Role::TextInput && n.value().as_deref() == Some("100%"))
+            .find(|n| (n.rect().center().y - row.center().y).abs() < 8.0)
+            .expect("the Tint field")
+            .click();
+        h.run_steps(2);
+        h.event(egui::Event::Key { key: egui::Key::A, physical_key: None, pressed: true, repeat: false, modifiers: egui::Modifiers::COMMAND });
+        h.event(egui::Event::Text("25".into()));
+        h.key_press(egui::Key::Enter);
+        h.run_steps(3);
+        let doc = &h.state().session.active().unwrap().doc;
+        let fill = |id: u64| doc.item(designcraft_doc::ids::ItemId(id)).unwrap().fill.clone();
+        assert_eq!((fill(a).swatch.as_str(), fill(a).tint), (CYAN, 0.25));
+        assert_eq!((fill(b).swatch.as_str(), fill(b).tint), ("[Black]", 0.25), "the second keeps its own swatch");
+    }
+
     #[test]
     fn apply_to_text_colours_a_text_frames_text_not_the_frame() {
         let mut app = DesignApp::new(designcraft_engine::Session::new(), crate::Services::default());