Merge pull request #3650 from insideTheFlux/fix/3381-title-bar

LR-BEHAV-TITLEBAR: the Windows title bar takes LightCraft's theme at launch (#3381)

crates/ui-egui/src/app/frame.rs

@@ -265,6 +265,7 @@ impl LightcraftApp {
             self.import_dropped_files(ctx);
         }
         self.check_external_editor(ctx);
+        theme::refresh_window_on_first_focus(ctx);
         // Alt (Option on macOS) while a slider is dragged shows its temporary preview
         self.ui.alt_held = ctx.input(|i| i.modifiers.alt);
         // Recent-library checks and launch-list keys read focus/time/keys: they belong to the UI

crates/ui-egui/src/theme.rs

@@ -412,6 +412,25 @@ pub fn current(ctx: &egui::Context) -> Option<ThemeKind> {
     ctx.data(|d| d.get_temp::<ThemeKind>(theme_id()))
 }
 
+/// Windows only: tell the window its theme again, the first time it has focus. A first theme that
+/// reaches a focused window as it comes up changes the title's colour but not the caption's, so
+/// with LightCraft dark on a light system the title is white on a light caption (it looks blank),
+/// and light on dark is dark on dark, until focus next moves (#3381). The same command repaints
+/// the caption once the window is up. A window that opens without focus shows the right colours
+/// from the start.
+pub fn refresh_window_on_first_focus(ctx: &egui::Context) {
+    let done = egui::Id::unique("lightcraft-window-theme-refreshed");
+    if !cfg!(target_os = "windows") || !ctx.input(|i| i.focused) || ctx.data(|d| d.get_temp::<bool>(done)).is_some() {
+        return;
+    }
+    ctx.data_mut(|d| d.insert_temp(done, true));
+    let theme = match ctx.theme() {
+        egui::Theme::Dark => egui::SystemTheme::Dark,
+        egui::Theme::Light => egui::SystemTheme::Light,
+    };
+    ctx.send_viewport_cmd(egui::ViewportCommand::SetTheme(theme));
+}
+
 /// Style `ctx` with the default theme.
 pub fn apply(ctx: &egui::Context) {
     apply_kind(ctx, ThemeKind::default());
@@ -506,6 +525,51 @@ mod tests {
         }
     }
 
+    /// The `SetTheme(Light)` commands one frame of `ctx` sends the window, with or without
+    /// [`refresh_window_on_first_focus`] in it.
+    #[cfg(target_os = "windows")]
+    fn light_theme_commands(ctx: &egui::Context, focused: bool, refresh: bool) -> usize {
+        let raw = egui::RawInput { focused, ..Default::default() };
+        let mut out = ctx.run_ui(raw, |ui| {
+            if refresh {
+                refresh_window_on_first_focus(ui.ctx());
+            }
+        });
+        out.textures_delta.clear();
+        let commands = out.viewport_output.remove(&egui::ViewportId::ROOT).map(|v| v.commands).unwrap_or_default();
+        commands.iter().filter(|c| matches!(c, egui::ViewportCommand::SetTheme(egui::SystemTheme::Light))).count()
+    }
+
+    /// #3381: egui sends the theme with the first frame, and the window hears it once more the
+    /// first time it has focus, not on every later focus.
+    #[cfg(target_os = "windows")]
+    #[test]
+    fn the_window_hears_its_theme_again_the_first_time_it_has_focus() {
+        let ctx = egui::Context::default();
+        apply_kind(&ctx, ThemeKind::Silver);
+        let sent = |focused: bool| light_theme_commands(&ctx, focused, true);
+        assert_eq!(sent(false), 1, "egui's own, with the first frame");
+        assert_eq!(sent(false), 0, "no focus yet");
+        assert_eq!(sent(true), 1, "the first frame with focus");
+        assert_eq!(sent(true), 0, "still focused");
+        assert_eq!(sent(false), 0, "focus lost");
+        assert_eq!(sent(true), 0, "focus back: Windows repaints this by itself");
+    }
+
+    /// #3381: a window that has focus from its very first frame hears the theme once more in that
+    /// frame, on top of egui's own command. (In the app the first frame never gets here: `ui`
+    /// returns before the fonts are ready, so egui's command always goes a frame earlier.)
+    #[cfg(target_os = "windows")]
+    #[test]
+    fn a_window_focused_from_its_first_frame_hears_its_theme_again_in_that_frame() {
+        let first_frame = |refresh: bool| {
+            let ctx = egui::Context::default();
+            apply_kind(&ctx, ThemeKind::Silver);
+            light_theme_commands(&ctx, true, refresh)
+        };
+        assert_eq!(first_frame(true), first_frame(false) + 1);
+    }
+
     /// Every theme scrolls 100 points a wheel notch, and a zoom notch stays egui's stock ~1.22x
     /// (`exp(40 / 200)`) instead of growing with the longer scroll.
     #[test]

docs/whats-new.md

@@ -12,6 +12,13 @@
   hot pixels on a sensor. Stars and other points of light that are kept don't count, so a dense star field still
   loses its hot pixels. Settings ▸ Performance ▸ Hot pixel limit sets the share (0.05 % to 1 %).
 
+## 2026-11-02
+
+### The Windows title bar is readable from the moment the window opens
+- When LightCraft's appearance differs from the one set in Windows (the dark default on a light Windows, for one), the
+  title bar kept the system's colour with the title in LightCraft's, so the title looked blank until focus moved to
+  another window. It now takes LightCraft's colours as soon as the window has focus.
+
 ## 2026-11-01
 
 ### Korean and Vietnamese text in exports draws whole