feat: add WindowExtWindows::has_undecorated_shadow on Windows (#1074)

.changes/has-undecorated-shadow.md

@@ -0,0 +1,5 @@
+---
+"tao": "patch"
+---
+
+On Windows, add `WindowExtWindows::has_undecorated_shadow` to check if window has shadows for undecorated window or not.

src/platform/windows.rs

@@ -182,6 +182,9 @@ 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);
 
+  /// Returns whether this window has shadow for undecorated windows.
+  fn has_undecorated_shadow(&self) -> bool;
+
   /// Sets right-to-left layout.
   ///
   /// Enabling this mainly flips the orientation of menus and title bar buttons
@@ -236,6 +239,11 @@ impl WindowExtWindows for Window {
     self.window.set_undecorated_shadow(shadow)
   }
 
+  #[inline]
+  fn has_undecorated_shadow(&self) -> bool {
+    self.window.has_undecorated_shadow()
+  }
+
   #[inline]
   fn set_rtl(&self, rtl: bool) {
     self.window.set_rtl(rtl)

src/platform_impl/windows/window.rs

@@ -1116,6 +1116,15 @@ impl Window {
     });
   }
 
+  #[inline]
+  pub fn has_undecorated_shadow(&self) -> bool {
+    self
+      .window_state
+      .lock()
+      .window_flags
+      .contains(WindowFlags::MARKER_UNDECORATED_SHADOW)
+  }
+
   pub fn set_content_protection(&self, enabled: bool) {
     unsafe {
       let _ = SetWindowDisplayAffinity(