Support right-to-left layout on Windows (#762)

* Support right-to-left layout on Windows

* Make RTL platform-specific

* Document RTL support on Windows

* RTL -> RIGHT_TO_LEFT_LAYOUT

* Add line about what set_rtl exactly does

* Fix formatting

Signed-off-by: Abdo <abdo@abdnh.net>

---------

Signed-off-by: Abdo <abdo@abdnh.net>

.changes/windows-rtl.md

@@ -0,0 +1,5 @@
+---
+"tao": "patch"
+---
+
+Add `WindowExtWindows::set_rtl` and `WindowBuilderExtWindows::with_rtl` to set right-to-left layout on Windows.

src/platform/windows.rs

@@ -121,6 +121,11 @@ pub trait WindowExtWindows {
   ///
   /// Enabling the shadow causes a thin 1px line to appear on the top of the window.
   fn set_undecorated_shadow(&self, shadow: bool);
+
+  /// Sets right-to-left layout.
+  ///
+  /// Enabling this mainly flips the orientation of menus and title bar buttons
+  fn set_rtl(&self, rtl: bool);
 }
 
 impl WindowExtWindows for Window {
@@ -170,6 +175,11 @@ impl WindowExtWindows for Window {
   fn set_undecorated_shadow(&self, shadow: bool) {
     self.window.set_undecorated_shadow(shadow)
   }
+
+  #[inline]
+  fn set_rtl(&self, rtl: bool) {
+    self.window.set_rtl(rtl)
+  }
 }
 
 /// Additional methods on `WindowBuilder` that are specific to Windows.
@@ -226,6 +236,9 @@ pub trait WindowBuilderExtWindows {
   /// The shadow is hidden by default.
   /// Enabling the shadow causes a thin 1px line to appear on the top of the window.
   fn with_undecorated_shadow(self, shadow: bool) -> WindowBuilder;
+
+  /// Sets right-to-left layout.
+  fn with_rtl(self, rtl: bool) -> WindowBuilder;
 }
 
 impl WindowBuilderExtWindows for WindowBuilder {
@@ -276,6 +289,12 @@ impl WindowBuilderExtWindows for WindowBuilder {
     self.platform_specific.decoration_shadow = shadow;
     self
   }
+
+  #[inline]
+  fn with_rtl(mut self, rtl: bool) -> WindowBuilder {
+    self.platform_specific.rtl = rtl;
+    self
+  }
 }
 
 /// Additional methods on `MonitorHandle` that are specific to Windows.

src/platform_impl/windows/mod.rs

@@ -51,6 +51,7 @@ pub struct PlatformSpecificWindowBuilderAttributes {
   pub drag_and_drop: bool,
   pub preferred_theme: Option<Theme>,
   pub decoration_shadow: bool,
+  pub rtl: bool,
 }
 
 impl Default for PlatformSpecificWindowBuilderAttributes {
@@ -64,6 +65,7 @@ impl Default for PlatformSpecificWindowBuilderAttributes {
       preferred_theme: None,
       skip_taskbar: false,
       decoration_shadow: true,
+      rtl: false,
     }
   }
 }

src/platform_impl/windows/window.rs

@@ -756,6 +756,17 @@ impl Window {
     });
   }
 
+  pub fn set_rtl(&self, rtl: bool) {
+    let window = self.window.clone();
+    let window_state = Arc::clone(&self.window_state);
+
+    self.thread_executor.execute_in_thread(move || {
+      WindowState::set_window_flags(window_state.lock(), window.0, |f| {
+        f.set(WindowFlags::RIGHT_TO_LEFT_LAYOUT, rtl)
+      });
+    });
+  }
+
   #[inline]
   pub fn current_monitor(&self) -> Option<RootMonitorHandle> {
     Some(RootMonitorHandle {
@@ -1010,6 +1021,8 @@ unsafe fn init<T: 'static>(
 
   window_flags.set(WindowFlags::MARKER_DONT_FOCUS, !attributes.focused);
 
+  window_flags.set(WindowFlags::RIGHT_TO_LEFT_LAYOUT, pl_attribs.rtl);
+
   let parent = match pl_attribs.parent {
     Parent::ChildOf(parent) => {
       window_flags.set(WindowFlags::CHILD, true);

src/platform_impl/windows/window_state.rs

@@ -107,6 +107,8 @@ bitflags! {
         /// Drop shadow for undecorated windows.
         const MARKER_UNDECORATED_SHADOW = 1 << 21;
 
+        const RIGHT_TO_LEFT_LAYOUT = 1 << 22;
+
         const EXCLUSIVE_FULLSCREEN_OR_MASK = WindowFlags::ALWAYS_ON_TOP.bits;
     }
 }
@@ -269,6 +271,9 @@ impl WindowFlags {
     ) {
       style &= !WS_OVERLAPPEDWINDOW;
     }
+    if self.contains(WindowFlags::RIGHT_TO_LEFT_LAYOUT) {
+      style_ex |= WS_EX_LAYOUTRTL | WS_EX_RTLREADING | WS_EX_RIGHT;
+    }
 
     (style, style_ex)
   }