Preferences: choose the interface font (#1408)

Adds an Interface font setting that leads the proportional family, with the default face and CJK/Hangul fallbacks kept behind it (#1290).

Co-authored-by: DuBearte <DuBearte@users.noreply.github.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/ui-egui/src/prefs.rs

@@ -292,6 +292,9 @@ pub struct Prefs {
     pub language: String,
     /// Interface scale (1 = 100 %).
     pub ui_scale: f32,
+    /// Interface font: an installed font family (or a font file), or empty for the built-in one
+    /// (#1290). Menus, dialogs and labels use it; glyphs it lacks fall back as before.
+    pub ui_font: String,
     /// Put the feature history above the parts browser in the left sidebar instead of along the
     /// bottom of the viewport.
     pub timeline_left: bool,
@@ -398,6 +401,7 @@ impl Default for Prefs {
             theme: "dark".into(),
             language: "en".into(),
             ui_scale: 1.0,
+            ui_font: String::new(),
             timeline_left: false,
             timeline_left_height: 360.0,
             timeline_left_browser_collapsed: false,
@@ -441,6 +445,8 @@ pub struct PrefsWindow {
     snapshot: Option<Snapshot>,
     /// The up axis preference the view follows now (applied when it changes, and at startup).
     applied_up: Option<String>,
+    /// The search text of the interface font list.
+    font_filter: String,
 }
 
 /// Open the dialog at a page.
@@ -504,6 +510,54 @@ impl Snapshot {
     }
 }
 
+/// The interface font (#1290): the built-in font first, then the installed families, with a
+/// search box. The choice applies at once, like the other preferences.
+fn ui_font_row(app: &mut SolveApp, ui: &mut egui::Ui) {
+    let builtin = app.tr_label("Built-in").to_string();
+    let current = if app.preferences.ui_font.trim().is_empty() { builtin.clone() } else { app.preferences.ui_font.clone() };
+    let families = crate::sketch_text::families(ui.ctx());
+    let mut chosen: Option<String> = None;
+    let combo = egui::ComboBox::from_id_salt("pref_ui_font")
+        .width(220.0)
+        .height(340.0)
+        .selected_text(current)
+        .close_behavior(egui::PopupCloseBehavior::CloseOnClickOutside)
+        .show_ui(ui, |ui| {
+            let search = egui::TextEdit::singleline(&mut app.prefs_window.font_filter).hint_text(crate::i18n::tr("sketch_text.font_search"));
+            ui.add(search.desired_width(f32::INFINITY));
+            let filter = app.prefs_window.font_filter.trim().to_lowercase();
+            egui::ScrollArea::vertical().max_height(280.0).min_scrolled_height(280.0).auto_shrink([false, false]).show(ui, |ui| {
+                if builtin.to_lowercase().contains(&filter) && ui.selectable_label(app.preferences.ui_font.trim().is_empty(), &builtin).clicked() {
+                    chosen = Some(String::new());
+                }
+                match &families {
+                    Some(list) => {
+                        for family in list.iter().filter(|f| f.to_lowercase().contains(&filter)) {
+                            let item = ui.selectable_label(app.preferences.ui_font == *family, family);
+                            crate::scenario::publish_handle(&format!("prefs:font:{family}"), item.rect.center());
+                            if item.clicked() {
+                                chosen = Some(family.clone());
+                            }
+                        }
+                    }
+                    None => {
+                        ui.label(crate::i18n::tr_label("Listing the installed fonts…"));
+                    }
+                }
+            });
+        });
+    crate::scenario::publish_handle("prefs:ui_font", combo.response.rect.center());
+    if let Some(name) = chosen {
+        if name.is_empty() || crate::fonts::ui_font(&name).is_some() {
+            app.preferences.ui_font = name;
+        } else {
+            app.set_status(format!("The font `{name}` could not be read"), true);
+        }
+        app.prefs_window.font_filter.clear();
+        ui.close();
+    }
+}
+
 /// Restore Defaults for one page.
 fn defaults(app: &mut SolveApp, page: usize) {
     let d = Prefs::default();
@@ -513,6 +567,7 @@ fn defaults(app: &mut SolveApp, page: usize) {
             p.theme = d.theme;
             p.language = d.language;
             p.ui_scale = d.ui_scale;
+            p.ui_font = d.ui_font;
             p.timeline_left = d.timeline_left;
             p.timeline_left_height = d.timeline_left_height;
             p.timeline_left_browser_collapsed = d.timeline_left_browser_collapsed;
@@ -1004,6 +1059,11 @@ fn page(app: &mut SolveApp, ui: &mut egui::Ui, t: &Tokens) {
             );
             crate::scenario::publish_rect("prefs:scale", scale.rect);
             ui.end_row();
+            if !cfg!(target_arch = "wasm32") {
+                ui.label(app.tr_label("Interface font"));
+                ui_font_row(app, ui);
+                ui.end_row();
+            }
             ui.label(app.tr("ui.feature_history"));
             let timeline_bottom = app.tr("ui.timeline_bottom").to_string();
             let timeline_left = app.tr("ui.timeline_left_sidebar").to_string();
@@ -1429,6 +1489,9 @@ pub fn set(app: &mut SolveApp, p: &serde_json::Value) -> Result<serde_json::Valu
     if !crate::i18n::is_supported(&new.language) {
         return Err(format!("`language` must be one of: {}", crate::i18n::LOCALES.iter().map(|locale| locale.id).collect::<Vec<_>>().join(", ")));
     }
+    if new.ui_font != app.preferences.ui_font && !new.ui_font.trim().is_empty() && crate::fonts::ui_font(&new.ui_font).is_none() {
+        return Err(format!("`ui_font`: `{}` is not an installed font family or a readable font file", new.ui_font.trim()));
+    }
     if !(0.5..=2.5).contains(&new.ui_scale) || !(0.25..=4.0).contains(&new.look_at_speed) {
         return Err("`ui_scale` must be 0.5…2.5 and `look_at_speed` 0.25…4".into());
     }
@@ -1458,6 +1521,26 @@ pub fn set(app: &mut SolveApp, p: &serde_json::Value) -> Result<serde_json::Valu
 
 #[cfg(test)]
 mod tests {
+    /// The interface font (#1290): a font that can be read, or empty for the built-in one; saved
+    /// with the others and reset by Restore Defaults.
+    #[test]
+    fn ui_font_is_checked_saved_and_restored() {
+        use serde_json::json;
+        let mut app = crate::SolveApp::new(solidcraft_engine::Session::default(), crate::Services::default());
+        assert_eq!(app.preferences.ui_font, "");
+        let family = solidcraft_engine::sketch::DEFAULT_FONT_FAMILY;
+        let out = super::set(&mut app, &json!({ "ui_font": family })).unwrap();
+        assert_eq!(out["ui_font"], family);
+        let e = super::set(&mut app, &json!({"ui_font": "No Such Font 1290"})).unwrap_err();
+        assert!(e.contains("ui_font"), "{e}");
+        assert_eq!(app.preferences.ui_font, family, "a refused font leaves the choice as it was");
+        let mut other = crate::SolveApp::new(solidcraft_engine::Session::default(), crate::Services::default());
+        other.load_prefs(&app.prefs());
+        assert_eq!(other.preferences.ui_font, family);
+        super::defaults(&mut app, 0);
+        assert_eq!(app.preferences.ui_font, "");
+    }
+
     #[test]
     fn number_fields_take_a_decimal_point_or_a_decimal_comma() {
         // #1347