Ability to force a theme on Windows (#1666)

src/platform/windows.rs

@@ -13,7 +13,7 @@ use crate::{
     event_loop::EventLoop,
     monitor::MonitorHandle,
     platform_impl::{EventLoop as WindowsEventLoop, WinIcon},
-    window::{BadIcon, Icon, Window, WindowBuilder},
+    window::{BadIcon, Icon, Theme, Window, WindowBuilder},
 };
 
 /// Additional methods on `EventLoop` that are specific to Windows.
@@ -81,8 +81,8 @@ pub trait WindowExtWindows {
     /// This sets `ICON_BIG`. A good ceiling here is 256x256.
     fn set_taskbar_icon(&self, taskbar_icon: Option<Icon>);
 
-    /// Whether the system theme is currently Windows 10's "Dark Mode".
-    fn is_dark_mode(&self) -> bool;
+    /// Returns the current window theme.
+    fn theme(&self) -> Theme;
 }
 
 impl WindowExtWindows for Window {
@@ -102,8 +102,8 @@ impl WindowExtWindows for Window {
     }
 
     #[inline]
-    fn is_dark_mode(&self) -> bool {
-        self.window.is_dark_mode()
+    fn theme(&self) -> Theme {
+        self.window.theme()
     }
 }
 
@@ -125,6 +125,9 @@ pub trait WindowBuilderExtWindows {
     /// If you need COM API with `COINIT_MULTITHREADED` you must initialize it before calling any winit functions.
     /// See https://docs.microsoft.com/en-us/windows/win32/api/objbase/nf-objbase-coinitialize#remarks for more information.
     fn with_drag_and_drop(self, flag: bool) -> WindowBuilder;
+
+    /// Forces a theme or uses the system settings if `None` was provided.
+    fn with_theme(self, theme: Option<Theme>) -> WindowBuilder;
 }
 
 impl WindowBuilderExtWindows for WindowBuilder {
@@ -151,6 +154,12 @@ impl WindowBuilderExtWindows for WindowBuilder {
         self.platform_specific.drag_and_drop = flag;
         self
     }
+
+    #[inline]
+    fn with_theme(mut self, theme: Option<Theme>) -> WindowBuilder {
+        self.platform_specific.preferred_theme = theme;
+        self
+    }
 }
 
 /// Additional methods on `MonitorHandle` that are specific to Windows.