Automatically enable AdjustIndistinguishableColors if High Contrast mode enabled (#17346)

If High Contrast mode is enabled in the OS settings, we now
automatically enable `adjustIndistinguishableColors`. To accomplish
this, a new `Automatic` value is added to
`adjustIndistinguishableColors`. When it's chosen, color nudging doesn't
occur in regular contrast sessions, but we interpret the value as
`Indexed` respectively.

The new default value is `AutomaticIndexed`. Meaning that regular
contrast sessions will see no difference in behavior. However, if they
switch to high contrast mode, Windows Terminal will interpret the value
as `Indexed` at runtime. This was chosen because `Always` is more
performance intensive.
  
## References and Relevant Issues
#12999

## Validation Steps Performed
✅ Toggling High Contrast mode immediately triggers an updated terminal
instance with `adjustIndistinguishableColors`

src/cascadia/TerminalControl/ControlCore.cpp

@@ -955,6 +955,11 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         }
     }
 
+    void ControlCore::SetHighContrastMode(const bool enabled)
+    {
+        _terminal->SetHighContrastMode(enabled);
+    }
+
     Control::IControlSettings ControlCore::Settings()
     {
         return *_settings;

src/cascadia/TerminalControl/ControlCore.h

@@ -94,6 +94,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         void UpdateSettings(const Control::IControlSettings& settings, const IControlAppearance& newAppearance);
         void ApplyAppearance(const bool focused);
+        void SetHighContrastMode(const bool enabled);
         Control::IControlSettings Settings();
         Control::IControlAppearance FocusedAppearance() const;
         Control::IControlAppearance UnfocusedAppearance() const;

src/cascadia/TerminalControl/ControlCore.idl

@@ -102,6 +102,7 @@ namespace Microsoft.Terminal.Control
         IControlAppearance FocusedAppearance { get; };
         IControlAppearance UnfocusedAppearance { get; };
         Boolean HasUnfocusedAppearance();
+        void SetHighContrastMode(Boolean enabled);
 
         UInt64 SwapChainHandle { get; };
 

src/cascadia/TerminalControl/TermControl.cpp

@@ -257,6 +257,12 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         return get_self<ControlCore>(_termControl->_core);
     }
 
+    static Windows::UI::ViewManagement::AccessibilitySettings& _GetAccessibilitySettings()
+    {
+        static Windows::UI::ViewManagement::AccessibilitySettings accessibilitySettings;
+        return accessibilitySettings;
+    }
+
     TermControl::TermControl(IControlSettings settings,
                              Control::IControlAppearance unfocusedAppearance,
                              TerminalConnection::ITerminalConnection connection) :
@@ -276,6 +282,16 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         _core = _interactivity.Core();
 
+        // If high contrast mode was changed, update the appearance appropriately.
+        _core.SetHighContrastMode(_GetAccessibilitySettings().HighContrast());
+        _revokers.HighContrastChanged = _GetAccessibilitySettings().HighContrastChanged(winrt::auto_revoke, [weakThis{ get_weak() }](const Windows::UI::ViewManagement::AccessibilitySettings& a11ySettings, auto&&) {
+            if (auto termControl = weakThis.get())
+            {
+                termControl->_core.SetHighContrastMode(a11ySettings.HighContrast());
+                termControl->_core.ApplyAppearance(termControl->_focused);
+            }
+        });
+
         // This event is specifically triggered by the renderer thread, a BG thread. Use a weak ref here.
         _revokers.RendererEnteredErrorState = _core.RendererEnteredErrorState(winrt::auto_revoke, { get_weak(), &TermControl::_RendererEnteredErrorState });
 

src/cascadia/TerminalControl/TermControl.h

@@ -362,7 +362,6 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         };
         bool _InitializeTerminal(const InitializeReason reason);
         safe_void_coroutine _restoreInBackground();
-        void _SetFontSize(int fontSize);
         void _TappedHandler(const Windows::Foundation::IInspectable& sender, const Windows::UI::Xaml::Input::TappedRoutedEventArgs& e);
         void _KeyDownHandler(const Windows::Foundation::IInspectable& sender, const Windows::UI::Xaml::Input::KeyRoutedEventArgs& e);
         void _KeyUpHandler(const Windows::Foundation::IInspectable& sender, const Windows::UI::Xaml::Input::KeyRoutedEventArgs& e);
@@ -394,8 +393,6 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         void _SwapChainSizeChanged(const Windows::Foundation::IInspectable& sender, const Windows::UI::Xaml::SizeChangedEventArgs& e);
         void _SwapChainScaleChanged(const Windows::UI::Xaml::Controls::SwapChainPanel& sender, const Windows::Foundation::IInspectable& args);
 
-        void _TerminalTabColorChanged(const std::optional<til::color> color);
-
         void _ScrollPositionChanged(const IInspectable& sender, const Control::ScrollPositionChangedArgs& args);
 
         bool _CapturePointer(const Windows::Foundation::IInspectable& sender, const Windows::UI::Xaml::Input::PointerRoutedEventArgs& e);
@@ -480,6 +477,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             // These are set up in _InitializeTerminal
             Control::ControlCore::RendererWarning_revoker RendererWarning;
             Control::ControlCore::SwapChainChanged_revoker SwapChainChanged;
+            Windows::UI::ViewManagement::AccessibilitySettings::HighContrastChanged_revoker HighContrastChanged;
 
             Control::ControlInteractivity::OpenHyperlink_revoker interactivityOpenHyperlink;
             Control::ControlInteractivity::ScrollPositionChanged_revoker interactivityScrollPositionChanged;

src/cascadia/TerminalCore/ICoreAppearance.idl

@@ -23,7 +23,8 @@ namespace Microsoft.Terminal.Core
     {
         Never,
         Indexed,
-        Always
+        Always,
+        Automatic
     };
 
     // TerminalCore declares its own Color struct to avoid depending

src/cascadia/TerminalCore/Terminal.cpp

@@ -143,7 +143,15 @@ void Terminal::UpdateAppearance(const ICoreAppearance& appearance)
     renderSettings.SetRenderMode(RenderSettings::Mode::IntenseIsBold, appearance.IntenseIsBold());
     renderSettings.SetRenderMode(RenderSettings::Mode::IntenseIsBright, appearance.IntenseIsBright());
 
-    switch (appearance.AdjustIndistinguishableColors())
+    // If AIC is set to Automatic,
+    // update the value based on if high contrast mode is enabled.
+    AdjustTextMode deducedAIC = appearance.AdjustIndistinguishableColors();
+    if (deducedAIC == AdjustTextMode::Automatic)
+    {
+        deducedAIC = _highContrastMode ? AdjustTextMode::Indexed : AdjustTextMode::Never;
+    }
+
+    switch (deducedAIC)
     {
     case AdjustTextMode::Always:
         renderSettings.SetRenderMode(RenderSettings::Mode::IndexedDistinguishableColors, false);
@@ -213,6 +221,11 @@ void Terminal::UpdateAppearance(const ICoreAppearance& appearance)
     _NotifyScrollEvent();
 }
 
+void Terminal::SetHighContrastMode(bool hc) noexcept
+{
+    _highContrastMode = hc;
+}
+
 void Terminal::SetCursorStyle(const DispatchTypes::CursorStyle cursorStyle)
 {
     auto& engine = reinterpret_cast<OutputStateMachineEngine&>(_stateMachine->Engine());

src/cascadia/TerminalCore/Terminal.hpp

@@ -92,6 +92,7 @@ public:
 
     void UpdateSettings(winrt::Microsoft::Terminal::Core::ICoreSettings settings);
     void UpdateAppearance(const winrt::Microsoft::Terminal::Core::ICoreAppearance& appearance);
+    void SetHighContrastMode(bool hc) noexcept;
     void SetFontInfo(const FontInfo& fontInfo);
     void SetCursorStyle(const ::Microsoft::Console::VirtualTerminal::DispatchTypes::CursorStyle cursorStyle);
     void SetVtChecksumReportSupport(const bool enabled);
@@ -382,6 +383,7 @@ private:
 
     std::wstring _answerbackMessage;
     std::wstring _workingDirectory;
+    bool _highContrastMode = false;
 
     // This default fake font value is only used to check if the font is a raster font.
     // Otherwise, the font is changed to a real value with the renderer via TriggerFontChange.

src/cascadia/TerminalSettingsEditor/Resources/en-US/Resources.resw

@@ -946,6 +946,10 @@
     <value>Always</value>
     <comment>An option to choose from for the "adjust indistinguishable colors" setting. When selected, we will adjust the text colors for visibility.</comment>
   </data>
+  <data name="Profile_AdjustIndistinguishableColorsAutomatic.Content" xml:space="preserve">
+    <value>Automatic</value>
+    <comment>An option to choose from for the "adjust indistinguishable colors" setting. When selected, we will adjust the text colors for visibility only when the colors are part of this profile's color scheme's color table if and only if high contrast mode is enabled.</comment>
+  </data>
   <data name="Profile_CursorShapeBar.Content" xml:space="preserve">
     <value>Bar ( ┃ )</value>
     <comment>{Locked="┃"} An option to choose from for the "cursor shape" setting. When selected, the cursor will look like a vertical bar. The character in the parentheses is used to show what it looks like.</comment>

src/cascadia/TerminalSettingsModel/MTSMSettings.h

@@ -136,7 +136,7 @@ Author(s):
     X(ConvergedAlignment, BackgroundImageAlignment, "backgroundImageAlignment", ConvergedAlignment::Horizontal_Center | ConvergedAlignment::Vertical_Center)       \
     X(hstring, BackgroundImagePath, "backgroundImage")                                                                                                             \
     X(Model::IntenseStyle, IntenseTextStyle, "intenseTextStyle", Model::IntenseStyle::Bright)                                                                      \
-    X(Core::AdjustTextMode, AdjustIndistinguishableColors, "adjustIndistinguishableColors", Core::AdjustTextMode::Never)                                           \
+    X(Core::AdjustTextMode, AdjustIndistinguishableColors, "adjustIndistinguishableColors", Core::AdjustTextMode::Automatic)                                       \
     X(bool, UseAcrylic, "useAcrylic", false)
 
 // Intentionally omitted Appearance settings:

src/cascadia/TerminalSettingsModel/TerminalSettingsSerializationHelpers.h

@@ -35,10 +35,11 @@ JSON_ENUM_MAPPER(::winrt::Microsoft::Terminal::Core::CursorStyle)
 // - Helper for converting a user-specified adjustTextMode value to its corresponding enum
 JSON_ENUM_MAPPER(::winrt::Microsoft::Terminal::Core::AdjustTextMode)
 {
-    JSON_MAPPINGS(3) = {
+    JSON_MAPPINGS(4) = {
         pair_type{ "never", ValueType::Never },
         pair_type{ "indexed", ValueType::Indexed },
         pair_type{ "always", ValueType::Always },
+        pair_type{ "automatic", ValueType::Automatic },
     };
 
     // Override mapping parser to add boolean parsing

src/cascadia/inc/ControlProperties.h

@@ -14,7 +14,7 @@
     X(til::color, SelectionBackground, DEFAULT_FOREGROUND)                                                                \
     X(bool, IntenseIsBold)                                                                                                \
     X(bool, IntenseIsBright, true)                                                                                        \
-    X(winrt::Microsoft::Terminal::Core::AdjustTextMode, AdjustIndistinguishableColors, winrt::Microsoft::Terminal::Core::AdjustTextMode::Never)
+    X(winrt::Microsoft::Terminal::Core::AdjustTextMode, AdjustIndistinguishableColors, winrt::Microsoft::Terminal::Core::AdjustTextMode::Automatic)
 
 // --------------------------- Control Appearance ---------------------------
 //  All of these settings are defined in IControlAppearance.