When enabling opacity on win10, automatically enable acrylic

src/cascadia/TerminalControl/ControlCore.cpp

@@ -442,6 +442,17 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         _settings.Opacity(newOpacity);
 
+        // GH#11285 - If the user is on Windows 10, and they changed the
+        // transparency of the control s.t. it should be partially opaque, then
+        // opt them in to acrylic. It's the only way to have transparency on
+        // Windows 10.
+        // We'll also turn the acrylic back off when they're fully opaque, which
+        // is what the Terminal did prior to 1.12.
+        if (!IsVintageOpacityAvailable())
+        {
+            _settings.UseAcrylic(newOpacity < 1.0);
+        }
+
         auto eventArgs = winrt::make_self<TransparencyChangedEventArgs>(newOpacity);
         _TransparencyChangedHandlers(*this, *eventArgs);
     }
@@ -570,6 +581,14 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         _settings = settings;
 
+        // GH#11285 - If the user is on Windows 10, and they wanted opacity, but
+        // didn't explicitly request acrylic, then opt them in to acrylic.
+        // On Windows 11+, this isn't needed, because we can have vintage opacity.
+        if (!IsVintageOpacityAvailable() && _settings.Opacity() < 1.0 && !_settings.UseAcrylic())
+        {
+            _settings.UseAcrylic(true);
+        }
+
         // Initialize our font information.
         const auto fontFace = _settings.FontFace();
         const short fontHeight = ::base::saturated_cast<short>(_settings.FontSize());
@@ -1545,4 +1564,20 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         return hstring(ss.str());
     }
+
+    // Helper to check if we're on Windows 11 or not. This is used to check if
+    // we need to use acrylic to achieve transparency, because vintage opacity
+    // doesn't work in islands on win10.
+    // Remove when we can remove the rest of GH#11285
+    bool ControlCore::IsVintageOpacityAvailable() noexcept
+    {
+        OSVERSIONINFOEXW osver{};
+        osver.dwOSVersionInfoSize = sizeof(osver);
+        osver.dwBuildNumber = 22000;
+
+        DWORDLONG dwlConditionMask = 0;
+        VER_SET_CONDITION(dwlConditionMask, VER_BUILDNUMBER, VER_GREATER_EQUAL);
+
+        return VerifyVersionInfoW(&osver, VER_BUILDNUMBER, dwlConditionMask) != FALSE;
+    }
 }

src/cascadia/TerminalControl/ControlCore.h

@@ -149,6 +149,8 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
         hstring ReadEntireBuffer() const;
 
+        static bool IsVintageOpacityAvailable() noexcept;
+
         // -------------------------------- WinRT Events ---------------------------------
         // clang-format off
         WINRT_CALLBACK(FontSizeChanged, Control::FontSizeChangedEventArgs);

src/cascadia/TerminalSettingsEditor/Profiles.cpp

@@ -47,6 +47,22 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
                 // NOTE: this is similar to what is done with BackgroundImagePath above
                 _NotifyChanges(L"UseParentProcessDirectory", L"UseCustomStartingDirectory");
             }
+            else if (viewModelProperty == L"UseAcrylic")
+            {
+                // GH#11372: If we're on Windows 10, and someone turns off
+                // acrylic, we're going to disable opacity for them. Opacity
+                // doesn't work without acrylic on Windows 10.
+                //
+                // BODGY: CascadiaSettings's function IsDefaultTerminalAvailable
+                // is basically a "are we on Windows 11" check, because defterm
+                // only works on Win11. So we'll use that.
+                //
+                // Remove when we can remove the rest of GH#11285
+                if (!UseAcrylic() && !CascadiaSettings::IsDefaultTerminalAvailable())
+                {
+                    Opacity(1.0);
+                }
+            }
         });
 
         // Do the same for the starting directory

src/cascadia/TerminalSettingsEditor/Profiles.h

@@ -23,6 +23,20 @@ namespace winrt::Microsoft::Terminal::Settings::Editor::implementation
         void SetAcrylicOpacityPercentageValue(double value)
         {
             Opacity(winrt::Microsoft::Terminal::Settings::Editor::Converters::PercentageValueToPercentage(value));
+
+            // GH#11372: If we're on Windows 10, and someone wants opacity, then
+            // we'll turn acrylic on for them. Opacity doesn't work without
+            // acrylic on Windows 10.
+            //
+            // BODGY: CascadiaSettings's function IsDefaultTerminalAvailable
+            // is basically a "are we on Windows 11" check, because defterm
+            // only works on Win11. So we'll use that.
+            //
+            // Remove when we can remove the rest of GH#11285
+            if (value < 100.0 && winrt::Microsoft::Terminal::Settings::Model::CascadiaSettings::IsDefaultTerminalAvailable())
+            {
+                UseAcrylic(true);
+            }
         };
 
         void SetPadding(double value)

src/cascadia/UnitTests_Control/ControlCoreTests.cpp

@@ -139,8 +139,11 @@ namespace ControlUnitTests
 
             // GH#603: Adjusting opacity shouldn't change whether or not we
             // requested acrylic.
-            VERIFY_IS_TRUE(settings->UseAcrylic());
-            VERIFY_IS_TRUE(core->_settings.UseAcrylic());
+
+            auto expectedUseAcrylic = winrt::Microsoft::Terminal::Control::implementation::ControlCore::IsVintageOpacityAvailable() ? true :
+                                                                                                                                      (expectedOpacity < 1.0 ? true : false);
+            VERIFY_ARE_EQUAL(expectedUseAcrylic, settings->UseAcrylic());
+            VERIFY_ARE_EQUAL(expectedUseAcrylic, core->_settings.UseAcrylic());
         };
         core->TransparencyChanged(opacityCallback);
 

src/cascadia/UnitTests_Control/ControlInteractivityTests.cpp

@@ -119,8 +119,10 @@ namespace ControlUnitTests
             VERIFY_ARE_EQUAL(expectedOpacity, settings->Opacity());
             VERIFY_ARE_EQUAL(expectedOpacity, core->_settings.Opacity());
 
-            VERIFY_ARE_EQUAL(useAcrylic, settings->UseAcrylic());
-            VERIFY_ARE_EQUAL(useAcrylic, core->_settings.UseAcrylic());
+            auto expectedUseAcrylic = winrt::Microsoft::Terminal::Control::implementation::ControlCore::IsVintageOpacityAvailable() ? useAcrylic :
+                                                                                                                                      (expectedOpacity < 1.0 ? true : false);
+            VERIFY_ARE_EQUAL(expectedUseAcrylic, settings->UseAcrylic());
+            VERIFY_ARE_EQUAL(expectedUseAcrylic, core->_settings.UseAcrylic());
         };
         core->TransparencyChanged(opacityCallback);