Use mica in the SUI if mica is enabled in the theme (#14567)

Does what it says on the tin!

Author: zadjii-msft

src/cascadia/TerminalSettingsEditor/MainPage.cpp

@@ -55,7 +55,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         _settingsClone{ settings.Copy() }
     {
         InitializeComponent();
-
+        _UpdateBackgroundForMica();
         _InitializeProfilesList();
 
         _colorSchemesPageVM = winrt::make<ColorSchemesPageViewModel>(_settingsClone);
@@ -102,6 +102,8 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         _settingsSource = settings;
         _settingsClone = settings.Copy();
 
+        _UpdateBackgroundForMica();
+
         // Deduce information about the currently selected item
         IInspectable lastBreadcrumb;
         const auto size = _breadcrumbs.Size();
@@ -640,4 +642,21 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         return SettingsNav().Background();
     }
 
+    // If the theme asks for Mica, then drop out our background, so that we
+    // can have mica too.
+    void MainPage::_UpdateBackgroundForMica()
+
+    {
+        const auto& theme = _settingsSource.GlobalSettings().CurrentTheme();
+
+        const auto bgKey = (theme.Window() != nullptr && theme.Window().UseMica()) ?
+                               L"SettingsPageMicaBackground" :
+                               L"SettingsPageBackground";
+
+        if (const auto bgColor = Resources().TryLookup(winrt::box_value(bgKey)))
+        {
+            SettingsNav().Background(winrt::WUX::Media::SolidColorBrush(winrt::unbox_value<Windows::UI::Color>(bgColor)));
+        }
+    }
+
 }

src/cascadia/TerminalSettingsEditor/MainPage.h

@@ -67,6 +67,8 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         void _Navigate(hstring clickedItemTag, BreadcrumbSubPage subPage);
         void _Navigate(const Editor::ProfileViewModel& profile, BreadcrumbSubPage subPage, const bool focusDeleteButton = false);
 
+        void _UpdateBackgroundForMica();
+
         winrt::Microsoft::Terminal::Settings::Editor::ColorSchemesPageViewModel _colorSchemesPageVM{ nullptr };
 
         Windows::UI::Xaml::Data::INotifyPropertyChanged::PropertyChanged_revoker _profileViewModelChangedRevoker;

src/cascadia/TerminalSettingsEditor/MainPage.xaml

@@ -31,16 +31,20 @@
 
                         <ResourceDictionary x:Key="Dark">
                             <Color x:Key="SettingsPageBackground">#282828</Color>
+                            <Color x:Key="SettingsPageMicaBackground">#00000000</Color>
                         </ResourceDictionary>
 
                         <ResourceDictionary x:Key="Light">
                             <Color x:Key="SettingsPageBackground">#F9F9F9</Color>
+                            <Color x:Key="SettingsPageMicaBackground">#00000000</Color>
                         </ResourceDictionary>
 
                         <ResourceDictionary x:Key="HighContrast">
                             <!--  Define resources for HighContrast mode here  -->
                             <StaticResource x:Key="SettingsPageBackground"
                                             ResourceKey="SystemColorWindowColorBrush" />
+                            <StaticResource x:Key="SettingsPageMicaBackground"
+                                            ResourceKey="SystemColorWindowColorBrush" />
                         </ResourceDictionary>
 
                     </ResourceDictionary.ThemeDictionaries>