fix(windows): use registry value to detect dark mode

Author: Slinetrac

winit-win32/Cargo.toml

@@ -39,6 +39,7 @@ windows-sys = { workspace = true, features = [
     "Win32_System_SystemServices",
     "Win32_System_Threading",
     "Win32_System_WindowsProgramming",
+    "Win32_System_Registry",
     "Win32_UI_Accessibility",
     "Win32_UI_Controls",
     "Win32_UI_HiDpi",

winit-win32/src/dark_mode.rs

@@ -3,8 +3,9 @@ use std::sync::LazyLock;
 /// which is inspired by the solution in https://github.com/ysc3839/win32-darkmode
 use std::{ffi::c_void, ptr};
 
-use windows_sys::Win32::Foundation::{BOOL, HWND, LPARAM, S_OK, WPARAM};
+use windows_sys::Win32::Foundation::{BOOL, ERROR_SUCCESS, HWND, LPARAM, S_OK, WPARAM};
 use windows_sys::Win32::System::LibraryLoader::{GetProcAddress, LoadLibraryA};
+use windows_sys::Win32::System::Registry::{HKEY_CURRENT_USER, RRF_RT_REG_DWORD, RegGetValueW};
 use windows_sys::Win32::UI::Accessibility::{HCF_HIGHCONTRASTON, HIGHCONTRASTA};
 use windows_sys::Win32::UI::Controls::SetWindowTheme;
 use windows_sys::Win32::UI::Input::KeyboardAndMouse::GetActiveWindow;
@@ -121,6 +122,13 @@ pub fn should_use_dark_mode() -> bool {
 }
 
 fn should_apps_use_dark_mode() -> bool {
+    if let Some(apps_use_light_theme) = read_apps_use_light_theme() {
+        return !apps_use_light_theme;
+    }
+
+    // This undocumented method `ShouldAppsUseDarkMode` may return
+    // incorrect values on Windows 11.
+    // See https://github.com/tauri-apps/tao/pull/1165
     type ShouldAppsUseDarkMode = unsafe extern "system" fn() -> bool;
     static SHOULD_APPS_USE_DARK_MODE: LazyLock<Option<ShouldAppsUseDarkMode>> =
         LazyLock::new(|| unsafe {
@@ -148,6 +156,24 @@ fn should_apps_use_dark_mode() -> bool {
         .unwrap_or(false)
 }
 
+fn read_apps_use_light_theme() -> Option<bool> {
+    let mut data: u32 = 0;
+    let mut data_size = std::mem::size_of::<u32>() as u32;
+    let status = unsafe {
+        RegGetValueW(
+            HKEY_CURRENT_USER,
+            w!(r"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize"),
+            w!("AppsUseLightTheme"),
+            RRF_RT_REG_DWORD,
+            ptr::null_mut(),
+            &mut data as *mut _ as _,
+            &mut data_size,
+        )
+    };
+
+    if status == ERROR_SUCCESS { Some(data != 0) } else { None }
+}
+
 fn is_high_contrast() -> bool {
     let mut hc = HIGHCONTRASTA { cbSize: 0, dwFlags: 0, lpszDefaultScheme: ptr::null_mut() };
 

winit/src/changelog/unreleased.md

@@ -48,3 +48,4 @@ changelog entry.
 
 - On X11, fix `set_hittest` not working on some window managers.
 - On Redox, handle `EINTR` when reading from `event_socket` instead of panicking.
+- On Windows, fix Dark/light theme detection sometimes isn't working.