fix(windows): blinking title bar on changing system settings

.changes/windows-theme-redraw-titlebar.md

@@ -0,0 +1,5 @@
+---
+"tao": patch
+---
+
+Fix blinking title bar when changing system settings on Windows

src/platform_impl/windows/dark_mode.rs

@@ -119,7 +119,11 @@ fn refresh_immersive_color_policy_state() {
 
 /// Attempt to set a theme on a window, if necessary.
 /// Returns the theme that was picked
-pub fn try_window_theme(hwnd: HWND, preferred_theme: Option<Theme>) -> Theme {
+pub fn try_window_theme(
+  hwnd: HWND,
+  preferred_theme: Option<Theme>,
+  redraw_title_bar: bool,
+) -> Theme {
   if *DARK_MODE_SUPPORTED {
     let is_dark_mode = match preferred_theme {
       Some(theme) => theme == Theme::Dark,
@@ -131,7 +135,7 @@ pub fn try_window_theme(hwnd: HWND, preferred_theme: Option<Theme>) -> Theme {
       false => Theme::Light,
     };
 
-    refresh_titlebar_theme_color(hwnd, is_dark_mode);
+    refresh_titlebar_theme_color(hwnd, is_dark_mode, redraw_title_bar);
 
     theme
   } else {
@@ -161,7 +165,7 @@ pub fn allow_dark_mode_for_window(hwnd: HWND, is_dark_mode: bool) {
   }
 }
 
-fn refresh_titlebar_theme_color(hwnd: HWND, is_dark_mode: bool) {
+fn refresh_titlebar_theme_color(hwnd: HWND, is_dark_mode: bool, redraw_title_bar: bool) {
   if let Some(ver) = *WIN10_BUILD_VERSION {
     if ver < 17763 {
       let mut is_dark_mode_bigbool: i32 = is_dark_mode.into();
@@ -187,12 +191,14 @@ fn refresh_titlebar_theme_color(hwnd: HWND, is_dark_mode: bool) {
           &dark_mode as *const BOOL as *const c_void,
           std::mem::size_of::<BOOL>() as u32,
         );
-        if GetActiveWindow() == hwnd {
-          DefWindowProcW(hwnd, WM_NCACTIVATE, None, None);
-          DefWindowProcW(hwnd, WM_NCACTIVATE, WPARAM(true.into()), None);
-        } else {
-          DefWindowProcW(hwnd, WM_NCACTIVATE, WPARAM(true.into()), None);
-          DefWindowProcW(hwnd, WM_NCACTIVATE, None, None);
+        if redraw_title_bar {
+          if GetActiveWindow() == hwnd {
+            DefWindowProcW(hwnd, WM_NCACTIVATE, None, None);
+            DefWindowProcW(hwnd, WM_NCACTIVATE, WPARAM(true.into()), None);
+          } else {
+            DefWindowProcW(hwnd, WM_NCACTIVATE, WPARAM(true.into()), None);
+            DefWindowProcW(hwnd, WM_NCACTIVATE, None, None);
+          }
         }
       }
     }

src/platform_impl/windows/event_loop.rs

@@ -335,7 +335,7 @@ impl<T> EventLoopWindowTarget<T> {
   pub fn set_theme(&self, theme: Option<Theme>) {
     *self.preferred_theme.lock() = theme;
     self.runner_shared.owned_windows(|window| {
-      let _ = unsafe { SendMessageW(window, WM_SETTINGCHANGE, WPARAM(0), LPARAM(0)) };
+      let _ = unsafe { SendMessageW(window, *CHANGE_THEME_MSG_ID, WPARAM(0), LPARAM(0)) };
     });
   }
 }
@@ -624,6 +624,11 @@ lazy_static! {
     pub static ref SET_RETAIN_STATE_ON_SIZE_MSG_ID: u32 = unsafe {
         RegisterWindowMessageA(s!("Tao::SetRetainMaximized"))
     };
+    /// Message sent by event loop when event loop's prefered theme changed.
+    /// WPARAM and LPARAM are unused.
+    pub static ref CHANGE_THEME_MSG_ID: u32 = unsafe {
+        RegisterWindowMessageA(s!("Tao::ChangeTheme"))
+    };
     /// When the taskbar is created, it registers a message with the "TaskbarCreated" string and then broadcasts this message to all top-level windows
     /// When the application receives this message, it should assume that any taskbar icons it added have been removed and add them again.
     pub static ref S_U_TASKBAR_RESTART: u32 = unsafe {
@@ -2072,23 +2077,7 @@ unsafe fn public_window_callback_inner<T: 'static>(
     }
 
     win32wm::WM_SETTINGCHANGE => {
-      use crate::event::WindowEvent::ThemeChanged;
-
-      let preferred_theme = subclass_input.window_state.lock().preferred_theme;
-      let new_theme = try_window_theme(
-        window,
-        preferred_theme.or(*subclass_input.event_loop_preferred_theme.lock()),
-      );
-      let mut window_state = subclass_input.window_state.lock();
-
-      if window_state.current_theme != new_theme {
-        window_state.current_theme = new_theme;
-        mem::drop(window_state);
-        subclass_input.send_event(Event::WindowEvent {
-          window_id: RootWindowId(WindowId(window.0 as _)),
-          event: ThemeChanged(new_theme),
-        });
-      }
+      update_theme(subclass_input, window, true);
     }
 
     win32wm::WM_NCCALCSIZE => {
@@ -2197,6 +2186,9 @@ unsafe fn public_window_callback_inner<T: 'static>(
           f.set(WindowFlags::MARKER_RETAIN_STATE_ON_SIZE, wparam.0 != 0)
         });
         result = ProcResult::Value(LRESULT(0));
+      } else if msg == *CHANGE_THEME_MSG_ID {
+        update_theme(subclass_input, window, false);
+        result = ProcResult::Value(LRESULT(0));
       } else if msg == *S_U_TASKBAR_RESTART {
         let window_state = subclass_input.window_state.lock();
         let _ = set_skip_taskbar(window, window_state.skip_taskbar);
@@ -2216,6 +2208,31 @@ unsafe fn public_window_callback_inner<T: 'static>(
   }
 }
 
+fn update_theme<T>(
+  subclass_input: &SubclassInput<T>,
+  window: HWND,
+  from_settings_change_event: bool,
+) {
+  let mut window_state = subclass_input.window_state.lock();
+  let preferred_theme = window_state
+    .preferred_theme
+    .or(*subclass_input.event_loop_preferred_theme.lock());
+  if from_settings_change_event && preferred_theme.is_some() {
+    return;
+  }
+  let new_theme = try_window_theme(window, preferred_theme, !from_settings_change_event);
+  if window_state.current_theme != new_theme {
+    window_state.current_theme = new_theme;
+    mem::drop(window_state);
+    unsafe {
+      subclass_input.send_event(Event::WindowEvent {
+        window_id: RootWindowId(WindowId(window.0 as _)),
+        event: WindowEvent::ThemeChanged(new_theme),
+      })
+    };
+  }
+}
+
 fn is_show_window_contents_while_dragging_enabled() -> bool {
   let mut is_enabled: BOOL = BOOL(0);
   let result = unsafe {

src/platform_impl/windows/window.rs

@@ -55,7 +55,10 @@ use crate::{
   },
 };
 
-use super::keyboard::{KeyEventBuilder, KEY_EVENT_BUILDERS};
+use super::{
+  event_loop::CHANGE_THEME_MSG_ID,
+  keyboard::{KeyEventBuilder, KEY_EVENT_BUILDERS},
+};
 
 /// A simple non-owning wrapper around a window.
 #[derive(Clone, Copy)]
@@ -940,7 +943,7 @@ impl Window {
       }
       window_state.preferred_theme = theme;
     }
-    unsafe { SendMessageW(self.hwnd(), WM_SETTINGCHANGE, WPARAM(0), LPARAM(0)) };
+    unsafe { SendMessageW(self.hwnd(), *CHANGE_THEME_MSG_ID, WPARAM(0), LPARAM(0)) };
   }
 
   #[inline]
@@ -1163,6 +1166,7 @@ unsafe fn init<T: 'static>(
     attributes
       .preferred_theme
       .or(*event_loop.preferred_theme.lock()),
+    false,
   );
 
   let window_state = {