Fix #4837: the saved color scheme, accent and canvas color show at launch

The first UI pass installed the default theme over the one the saved
preferences had applied earlier in the same frame, and later frames saw
the preferences as already applied. Classic, a non-default accent and a
Canvas Color showed as the defaults until a preference changed, and again
after the app took a new graphics context. The first pass now applies the
saved preferences.

crates/ui-egui/src/app.rs

@@ -400,7 +400,8 @@ impl VectorcraftApp {
         crate::ime::install_hooks(ctx);
         self.adopt_context(ctx);
         if !self.styled {
-            theme::apply(ctx, self.ui.brightness);
+            // The saved accent, color scheme and canvas color, not the defaults (#4837).
+            prefs_dialog::reapply(self, ctx);
             egui_extras::install_image_loaders(ctx);
             self.styled = true;
         }

crates/ui-egui/src/prefs_dialog.rs

@@ -125,7 +125,7 @@ pub fn apply_runtime(app: &mut VectorcraftApp, ctx: &egui::Context) {
         scrub: p.scrub_numeric_fields,
         bare_points: p.numbers_without_units_are_points,
     };
-    let id = egui::Id::unique("dc-applied-prefs");
+    let id = applied_id();
     let prev: Option<Applied> = ctx.data(|d| d.get_temp::<Option<Applied>>(id)).flatten();
     if prev != Some(want) {
         theme::apply_with(ctx, want.brightness, want.accent, want.scheme);
@@ -160,6 +160,18 @@ pub fn apply_runtime(app: &mut VectorcraftApp, ctx: &egui::Context) {
     }
 }
 
+/// Where [`apply_runtime`] keeps the preferences it last pushed into `ctx`.
+fn applied_id() -> egui::Id {
+    egui::Id::unique("dc-applied-prefs")
+}
+
+/// [`apply_runtime`] with nothing recorded as applied, so the theme (brightness, accent, color
+/// scheme and canvas color) and the other UI-side preferences are pushed into `ctx` again.
+pub(crate) fn reapply(app: &mut VectorcraftApp, ctx: &egui::Context) {
+    ctx.data_mut(|d| d.remove::<Option<Applied>>(applied_id()));
+    apply_runtime(app, ctx);
+}
+
 pub fn show(app: &mut VectorcraftApp, ctx: &egui::Context) {
     let Some(mut d) = app.ui.dialog.clone() else { return };
     let t = Tokens::get(ctx);

crates/ui-egui/src/prefs_dialog/tests.rs

@@ -60,6 +60,25 @@ fn canvas_color_choices_paint_the_pasteboard() {
     assert!(app.run("prefs.set", serde_json::json!({"key": "canvasColor", "value": "pink"})).is_err());
 }
 
+/// #4837: the saved Color Scheme, Accent and Canvas Color are the ones the first frame shows, not
+/// the defaults the first UI pass installs.
+#[test]
+fn saved_scheme_accent_and_canvas_color_show_from_the_first_frame() {
+    let mut app = app();
+    for (key, value) in [("uiColorScheme", "classic"), ("uiAccent", "pink"), ("canvasColor", "white")] {
+        app.run("prefs.set", json!({"key": key, "value": value})).unwrap();
+    }
+    let ctx = egui::Context::default();
+    for _ in 0..2 {
+        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| app.logic(ui.ctx()));
+        out.textures_delta.clear();
+        let (t, classic) = (Tokens::get(&ctx), Tokens::for_scheme(Scheme::Classic, app.ui.brightness, Accent::Pink));
+        assert_eq!((t.accent, t.app_bar, t.panel), (classic.accent, classic.app_bar, classic.panel));
+        assert_eq!(t.pasteboard, egui::Color32::WHITE);
+        assert_eq!(ctx.global_style().visuals.hyperlink_color, classic.accent);
+    }
+}
+
 fn app() -> VectorcraftApp {
     VectorcraftApp::new(Session::new(), Services::default())
 }