Detect likely Powerline fonts, add a special powerline preview (#15365)

When we detect a font that has a glyph for `U+E0B6`, we will switch the
preview connection text to contain a special powerline prompt. This will
allow people to see how different settings might impact their real-world
environment.

When we _don't_ detect such support, we fall back to the CMD-style
`C:\>` prompt.

Pros:
- It's beautiful.

Cons:
- More code

Risks:
- `U+E0B6` is part of the private use area, and fonts that have symbols
there (such as Cirth as sub-allocated by the ConScript Unicode Registry)
will result in something unexpected.
- Actually, `E0B6` isn't part of base powerline... but I think this
specific set of characters looks too good to pass up.

(cherry picked from commit 37e8aff)
Service-Card-Id: 89468351
Service-Version: 1.18

.github/actions/spelling/allow/allow.txt

@@ -78,6 +78,8 @@ ok'd
 overlined
 pipeline
 postmodern
+Powerline
+powerline
 ptys
 qof
 qps

src/cascadia/TerminalSettingsEditor/Appearances.cpp

@@ -20,6 +20,28 @@ using namespace winrt::Microsoft::Terminal::Settings::Model;
 
 namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
 {
+    bool Font::HasPowerlineCharacters()
+    {
+        if (!_hasPowerlineCharacters.has_value())
+        {
+            try
+            {
+                winrt::com_ptr<IDWriteFont> font;
+                THROW_IF_FAILED(_family->GetFont(0, font.put()));
+                BOOL exists{};
+                // We're actually checking for the "Extended" PowerLine glyph set.
+                // They're more fun.
+                THROW_IF_FAILED(font->HasCharacter(0xE0B6, &exists));
+                _hasPowerlineCharacters = (exists == TRUE);
+            }
+            catch (...)
+            {
+                _hasPowerlineCharacters = false;
+            }
+        }
+        return _hasPowerlineCharacters.value_or(false);
+    }
+
     AppearanceViewModel::AppearanceViewModel(const Model::AppearanceConfig& appearance) :
         _appearance{ appearance }
     {
@@ -288,25 +310,9 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
 
     IInspectable Appearances::CurrentFontFace() const
     {
-        // look for the current font in our shown list of fonts
         const auto& appearanceVM{ Appearance() };
         const auto appearanceFontFace{ appearanceVM.FontFace() };
-        const auto& currentFontList{ ShowAllFonts() ? ProfileViewModel::CompleteFontList() : ProfileViewModel::MonospaceFontList() };
-        IInspectable fallbackFont;
-        for (const auto& font : currentFontList)
-        {
-            if (font.LocalizedName() == appearanceFontFace)
-            {
-                return box_value(font);
-            }
-            else if (font.LocalizedName() == L"Cascadia Mono")
-            {
-                fallbackFont = box_value(font);
-            }
-        }
-
-        // we couldn't find the desired font, set to "Cascadia Mono" since that ships by default
-        return fallbackFont;
+        return box_value(ProfileViewModel::FindFontWithLocalizedName(appearanceFontFace));
     }
 
     void Appearances::FontFace_SelectionChanged(const IInspectable& /*sender*/, const SelectionChangedEventArgs& e)

src/cascadia/TerminalSettingsEditor/Appearances.h

@@ -36,14 +36,22 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
     struct Font : FontT<Font>
     {
     public:
-        Font(std::wstring name, std::wstring localizedName) :
+        Font(std::wstring name, std::wstring localizedName, IDWriteFontFamily* family) :
             _Name{ name },
-            _LocalizedName{ localizedName } {};
+            _LocalizedName{ localizedName }
+        {
+            _family.copy_from(family);
+        }
 
         hstring ToString() { return _LocalizedName; }
+        bool HasPowerlineCharacters();
 
         WINRT_PROPERTY(hstring, Name);
         WINRT_PROPERTY(hstring, LocalizedName);
+
+    private:
+        winrt::com_ptr<IDWriteFontFamily> _family;
+        std::optional<bool> _hasPowerlineCharacters;
     };
 
     struct AppearanceViewModel : AppearanceViewModelT<AppearanceViewModel>, ViewModelHelper<AppearanceViewModel>

src/cascadia/TerminalSettingsEditor/Appearances.idl

@@ -19,6 +19,7 @@ namespace Microsoft.Terminal.Settings.Editor
     {
         String Name { get; };
         String LocalizedName { get; };
+        Boolean HasPowerlineCharacters { get; };
     }
 
     runtimeclass AppearanceViewModel : Windows.UI.Xaml.Data.INotifyPropertyChanged

src/cascadia/TerminalSettingsEditor/PreviewConnection.cpp

@@ -8,15 +8,20 @@
 using namespace ::winrt::Microsoft::Terminal::TerminalConnection;
 using namespace ::winrt::Windows::Foundation;
 
+static constexpr std::wstring_view PromptTextPlain{ L"C:\\> " };
+static constexpr std::wstring_view PromptTextPowerline{ L"\x1b[49;34m\xe0b6\x1b[1;97;44m C:\\ \x1b[m\x1b[46;34m\xe0b8\x1b[49;36m\xe0b8\x1b[m " };
+
 // clang-format off
 static constexpr std::wstring_view PreviewText{
+    L"\x001b"
+    L"c" // Hard Reset (RIS); on separate lines to avoid becoming 0x01BC
     L"Windows Terminal\r\n"
-    L"C:\\> \x1b[93m" L"git\x1b[m diff \x1b[90m-w\x1b[m\r\n"
+    L"{0}\x1b[93m" L"git\x1b[m diff \x1b[90m-w\x1b[m\r\n"
     L"\x1b[1m" L"diff --git a/win b/win\x1b[m\r\n"
     L"\x1b[36m@@ -1 +1 @@\x1b[m\r\n"
     L"\x1b[31m-    Windows Console\x1b[m\r\n"
     L"\x1b[32m+    Windows Terminal!\x1b[m\r\n"
-    L"C:\\> \x1b[93mWrite-Host \x1b[36m\"\xd83c\xdf2f!\"\x1b[1D\x1b[m"
+    L"{0}\x1b[93mWrite-Host \x1b[36m\"\xd83c\xdf2f!\"\x1b[1D\x1b[m"
 };
 // clang-format on
 
@@ -27,7 +32,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
     void PreviewConnection::Start() noexcept
     {
         // Send the preview text
-        _TerminalOutputHandlers(PreviewText);
+        _TerminalOutputHandlers(fmt::format(PreviewText, _displayPowerlineGlyphs ? PromptTextPowerline : PromptTextPlain));
     }
 
     void PreviewConnection::Initialize(const Windows::Foundation::Collections::ValueSet& /*settings*/) noexcept
@@ -45,4 +50,13 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
     void PreviewConnection::Close() noexcept
     {
     }
+
+    void PreviewConnection::DisplayPowerlineGlyphs(bool d) noexcept
+    {
+        if (_displayPowerlineGlyphs != d)
+        {
+            _displayPowerlineGlyphs = d;
+            Start();
+        }
+    }
 }

src/cascadia/TerminalSettingsEditor/PreviewConnection.h

@@ -27,9 +27,14 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         void Resize(uint32_t rows, uint32_t columns) noexcept;
         void Close() noexcept;
 
+        void DisplayPowerlineGlyphs(bool d) noexcept;
+
         winrt::Microsoft::Terminal::TerminalConnection::ConnectionState State() const noexcept { return winrt::Microsoft::Terminal::TerminalConnection::ConnectionState::Connected; }
 
         WINRT_CALLBACK(TerminalOutput, winrt::Microsoft::Terminal::TerminalConnection::TerminalOutputHandler);
         TYPED_EVENT(StateChanged, winrt::Microsoft::Terminal::TerminalConnection::ITerminalConnection, IInspectable);
+
+    private:
+        bool _displayPowerlineGlyphs{ false };
     };
 }

src/cascadia/TerminalSettingsEditor/ProfileViewModel.cpp

@@ -21,6 +21,8 @@ using namespace winrt::Microsoft::Terminal::Settings::Model;
 
 namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
 {
+    static Editor::Font _FontObjectForDWriteFont(IDWriteFontFamily* family);
+
     Windows::Foundation::Collections::IObservableVector<Editor::Font> ProfileViewModel::_MonospaceFontList{ nullptr };
     Windows::Foundation::Collections::IObservableVector<Editor::Font> ProfileViewModel::_FontList{ nullptr };
 
@@ -118,12 +120,8 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
                 com_ptr<IDWriteFontFamily> fontFamily;
                 THROW_IF_FAILED(fontCollection->GetFontFamily(i, fontFamily.put()));
 
-                // get the font's localized names
-                com_ptr<IDWriteLocalizedStrings> localizedFamilyNames;
-                THROW_IF_FAILED(fontFamily->GetFamilyNames(localizedFamilyNames.put()));
-
                 // construct a font entry for tracking
-                if (const auto fontEntry{ _GetFont(localizedFamilyNames) })
+                if (const auto fontEntry{ _FontObjectForDWriteFont(fontFamily.get()) })
                 {
                     // check if the font is monospaced
                     try
@@ -159,7 +157,32 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
     }
     CATCH_LOG();
 
-    Editor::Font ProfileViewModel::_GetFont(com_ptr<IDWriteLocalizedStrings> localizedFamilyNames)
+    Editor::Font ProfileViewModel::FindFontWithLocalizedName(const winrt::hstring& name) noexcept
+    {
+        // look for the current font in our shown list of fonts
+        Editor::Font fallbackFont{ nullptr };
+        try
+        {
+            const auto& currentFontList{ CompleteFontList() };
+            for (const auto& font : currentFontList)
+            {
+                if (font.LocalizedName() == name)
+                {
+                    return font;
+                }
+                else if (font.LocalizedName() == L"Cascadia Mono")
+                {
+                    fallbackFont = font;
+                }
+            }
+        }
+        CATCH_LOG();
+
+        // we couldn't find the desired font, set to "Cascadia Mono" if we found that since it ships by default
+        return fallbackFont;
+    }
+
+    static Editor::Font _FontObjectForDWriteFont(IDWriteFontFamily* family)
     {
         // used for the font's name as an identifier (i.e. text block's font family property)
         std::wstring nameID;
@@ -169,6 +192,10 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         std::wstring localizedName;
         UINT32 localizedNameIndex;
 
+        // get the font's localized names
+        winrt::com_ptr<IDWriteLocalizedStrings> localizedFamilyNames;
+        THROW_IF_FAILED(family->GetFamilyNames(localizedFamilyNames.put()));
+
         // use our current locale to find the localized name
         auto exists{ FALSE };
         HRESULT hr;
@@ -211,7 +238,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
 
         if (!nameID.empty() && !localizedName.empty())
         {
-            return make<Font>(nameID, localizedName);
+            return make<Font>(nameID, localizedName, family);
         }
         return nullptr;
     }

src/cascadia/TerminalSettingsEditor/ProfileViewModel.h

@@ -34,6 +34,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         static void UpdateFontList() noexcept;
         static Windows::Foundation::Collections::IObservableVector<Editor::Font> CompleteFontList() noexcept { return _FontList; };
         static Windows::Foundation::Collections::IObservableVector<Editor::Font> MonospaceFontList() noexcept { return _MonospaceFontList; };
+        static Editor::Font FindFontWithLocalizedName(winrt::hstring const& name) noexcept;
 
         ProfileViewModel(const Model::Profile& profile, const Model::CascadiaSettings& settings);
         Model::TerminalSettings TermSettings() const;
@@ -123,8 +124,6 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         static Windows::Foundation::Collections::IObservableVector<Editor::Font> _MonospaceFontList;
         static Windows::Foundation::Collections::IObservableVector<Editor::Font> _FontList;
 
-        static Editor::Font _GetFont(com_ptr<IDWriteLocalizedStrings> localizedFamilyNames);
-
         Model::CascadiaSettings _appSettings;
         Editor::AppearanceViewModel _unfocusedAppearanceViewModel;
     };

src/cascadia/TerminalSettingsEditor/ProfileViewModel.idl

@@ -36,6 +36,7 @@ namespace Microsoft.Terminal.Settings.Editor
     {
         static Windows.Foundation.Collections.IObservableVector<Font> CompleteFontList { get; };
         static Windows.Foundation.Collections.IObservableVector<Font> MonospaceFontList { get; };
+        static Font FindFontWithLocalizedName(String name);
 
         Microsoft.Terminal.Settings.Model.TerminalSettings TermSettings { get; };
 

src/cascadia/TerminalSettingsEditor/Profiles_Appearance.cpp

@@ -19,6 +19,7 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
     Profiles_Appearance::Profiles_Appearance()
     {
         InitializeComponent();
+        _previewConnection = winrt::make_self<PreviewConnection>();
     }
 
     void Profiles_Appearance::OnNavigatedTo(const NavigationEventArgs& e)
@@ -36,7 +37,8 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         if (!_previewControl)
         {
             const auto settings = _Profile.TermSettings();
-            _previewControl = Control::TermControl(settings, settings, make<PreviewConnection>());
+            _previewConnection->DisplayPowerlineGlyphs(_looksLikePowerlineFont());
+            _previewControl = Control::TermControl(settings, settings, *_previewConnection);
             _previewControl.IsEnabled(false);
             _previewControl.AllowFocusWhenDisabled(false);
             _previewControl.DisplayCursorWhileBlurred(true);
@@ -68,9 +70,25 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         _Profile.DeleteUnfocusedAppearance();
     }
 
+    bool Profiles_Appearance::_looksLikePowerlineFont() const
+    {
+        if (_Profile && _Profile.DefaultAppearance())
+        {
+            if (const auto fontName = _Profile.DefaultAppearance().FontFace(); !fontName.empty())
+            {
+                if (const auto font = ProfileViewModel::FindFontWithLocalizedName(fontName))
+                {
+                    return font.HasPowerlineCharacters();
+                }
+            }
+        }
+        return false;
+    }
+
     void Profiles_Appearance::_onProfilePropertyChanged(const IInspectable&, const PropertyChangedEventArgs&) const
     {
         const auto settings = _Profile.TermSettings();
+        _previewConnection->DisplayPowerlineGlyphs(_looksLikePowerlineFont());
         _previewControl.UpdateControlSettings(settings, settings);
     }
 }

src/cascadia/TerminalSettingsEditor/Profiles_Appearance.h

@@ -5,6 +5,7 @@
 
 #include "Profiles_Appearance.g.h"
 #include "Utils.h"
+#include "PreviewConnection.h"
 
 namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
 {
@@ -26,7 +27,9 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
 
     private:
         void _onProfilePropertyChanged(const IInspectable&, const PropertyChangedEventArgs&) const;
+        bool _looksLikePowerlineFont() const;
 
+        winrt::com_ptr<PreviewConnection> _previewConnection{ nullptr };
         Microsoft::Terminal::Control::TermControl _previewControl{ nullptr };
         Windows::UI::Xaml::Data::INotifyPropertyChanged::PropertyChanged_revoker _ViewModelChangedRevoker;
         Windows::UI::Xaml::Data::INotifyPropertyChanged::PropertyChanged_revoker _AppearanceViewModelChangedRevoker;