Add support for fullscreen launchMode (#6060)

## Summary of the Pull Request

Adds `"launchMode": "fullscreen"`, which does what it says on the box.

## PR Checklist
* [x] Closes #288
* [x] I work here
* [ ] Tests added/passed
* [n/a] Requires documentation to be updated

## Detailed Description of the Pull Request / Additional comments

It's important to let the winow get created, _then_ fullscreen it, because otherwise, when the user exits fullscreen, the window is sized to like, 0x0 or something, and that's just annoying.

src/cascadia/TerminalApp/AppLogic.idl

@@ -11,6 +11,7 @@ namespace TerminalApp
     {
         DefaultMode,
         MaximizedMode,
+        FullscreenMode,
     };
 
     [default_interface] runtimeclass AppLogic : IF7Listener

src/cascadia/TerminalApp/GlobalAppSettings.cpp

@@ -38,6 +38,7 @@ static constexpr std::string_view ConfirmCloseAllKey{ "confirmCloseAllTabs" };
 static constexpr std::string_view SnapToGridOnResizeKey{ "snapToGridOnResize" };
 static constexpr std::wstring_view DefaultLaunchModeValue{ L"default" };
 static constexpr std::wstring_view MaximizedLaunchModeValue{ L"maximized" };
+static constexpr std::wstring_view FullscreenLaunchModeValue{ L"fullscreen" };
 static constexpr std::wstring_view LightThemeValue{ L"light" };
 static constexpr std::wstring_view DarkThemeValue{ L"dark" };
 static constexpr std::wstring_view SystemThemeValue{ L"system" };
@@ -473,6 +474,10 @@ LaunchMode GlobalAppSettings::_ParseLaunchMode(const std::wstring& launchModeStr
     {
         return LaunchMode::MaximizedMode;
     }
+    else if (launchModeString == FullscreenLaunchModeValue)
+    {
+        return LaunchMode::FullscreenMode;
+    }
 
     return LaunchMode::DefaultMode;
 }
@@ -490,6 +495,8 @@ std::wstring_view GlobalAppSettings::_SerializeLaunchMode(const LaunchMode launc
     {
     case LaunchMode::MaximizedMode:
         return MaximizedLaunchModeValue;
+    case LaunchMode::FullscreenMode:
+        return FullscreenLaunchModeValue;
     default:
         return DefaultLaunchModeValue;
     }

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -188,8 +188,8 @@ namespace winrt::TerminalApp::implementation
             if (_appArgs.GetStartupActions().empty())
             {
                 _OpenNewTab(nullptr);
-                _startupState = StartupState::Initialized;
-                _InitializedHandlers(*this, nullptr);
+
+                _CompleteInitialization();
             }
             else
             {
@@ -222,9 +222,31 @@ namespace winrt::TerminalApp::implementation
             {
                 _actionDispatch->DoAction(action);
             }
-            _startupState = StartupState::Initialized;
-            _InitializedHandlers(*this, nullptr);
+
+            _CompleteInitialization();
+        }
+    }
+
+    // Method Description:
+    // - Perform and steps that need to be done once our initial state is all
+    //   set up. This includes entering fullscreen mode and firing our
+    //   Initialized event.
+    // Arguments:
+    // - <none>
+    // Return Value:
+    // - <none>
+    void TerminalPage::_CompleteInitialization()
+    {
+        // GH#288 - When we finish initialization, if the user wanted us
+        // launched _fullscreen_, toggle fullscreen mode. This will make sure
+        // that the window size is _first_ set up as something sensible, so
+        // leaving fullscreen returns to a reasonable size.
+        if (_settings->GlobalSettings().GetLaunchMode() == winrt::TerminalApp::LaunchMode::FullscreenMode)
+        {
+            _ToggleFullscreen();
         }
+        _startupState = StartupState::Initialized;
+        _InitializedHandlers(*this, nullptr);
     }
 
     // Method Description:

src/cascadia/TerminalApp/TerminalPage.h

@@ -173,6 +173,8 @@ namespace winrt::TerminalApp::implementation
         void _SetNewTabButtonColor(const Windows::UI::Color& color, const Windows::UI::Color& accentColor);
         void _ClearNewTabButtonColor();
 
+        void _CompleteInitialization();
+
 #pragma region ActionHandlers
         // These are all defined in AppActionHandlers.cpp
         void _HandleOpenNewTabDropdown(const IInspectable& sender, const TerminalApp::ActionEventArgs& args);

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -239,61 +239,59 @@ void AppHost::_HandleCreateWindow(const HWND hwnd, RECT proposedRect, winrt::Ter
 
     long adjustedHeight = 0;
     long adjustedWidth = 0;
-    if (launchMode == winrt::TerminalApp::LaunchMode::DefaultMode)
+
+    // Find nearest monitor.
+    HMONITOR hmon = MonitorFromRect(&proposedRect, MONITOR_DEFAULTTONEAREST);
+
+    // Get nearest monitor information
+    MONITORINFO monitorInfo;
+    monitorInfo.cbSize = sizeof(MONITORINFO);
+    GetMonitorInfo(hmon, &monitorInfo);
+
+    // This API guarantees that dpix and dpiy will be equal, but neither is an
+    // optional parameter so give two UINTs.
+    UINT dpix = USER_DEFAULT_SCREEN_DPI;
+    UINT dpiy = USER_DEFAULT_SCREEN_DPI;
+    // If this fails, we'll use the default of 96.
+    GetDpiForMonitor(hmon, MDT_EFFECTIVE_DPI, &dpix, &dpiy);
+
+    // We need to check if the top left point of the titlebar of the window is within any screen
+    RECT offScreenTestRect;
+    offScreenTestRect.left = proposedRect.left;
+    offScreenTestRect.top = proposedRect.top;
+    offScreenTestRect.right = offScreenTestRect.left + 1;
+    offScreenTestRect.bottom = offScreenTestRect.top + 1;
+
+    bool isTitlebarIntersectWithMonitors = false;
+    EnumDisplayMonitors(
+        nullptr, &offScreenTestRect, [](HMONITOR, HDC, LPRECT, LPARAM lParam) -> BOOL {
+            auto intersectWithMonitor = reinterpret_cast<bool*>(lParam);
+            *intersectWithMonitor = true;
+            // Continue the enumeration
+            return FALSE;
+        },
+        reinterpret_cast<LPARAM>(&isTitlebarIntersectWithMonitors));
+
+    if (!isTitlebarIntersectWithMonitors)
     {
-        // Find nearest monitor.
-        HMONITOR hmon = MonitorFromRect(&proposedRect, MONITOR_DEFAULTTONEAREST);
-
-        // Get nearest monitor information
-        MONITORINFO monitorInfo;
-        monitorInfo.cbSize = sizeof(MONITORINFO);
-        GetMonitorInfo(hmon, &monitorInfo);
-
-        // This API guarantees that dpix and dpiy will be equal, but neither is an
-        // optional parameter so give two UINTs.
-        UINT dpix = USER_DEFAULT_SCREEN_DPI;
-        UINT dpiy = USER_DEFAULT_SCREEN_DPI;
-        // If this fails, we'll use the default of 96.
-        GetDpiForMonitor(hmon, MDT_EFFECTIVE_DPI, &dpix, &dpiy);
-
-        // We need to check if the top left point of the titlebar of the window is within any screen
-        RECT offScreenTestRect;
-        offScreenTestRect.left = proposedRect.left;
-        offScreenTestRect.top = proposedRect.top;
-        offScreenTestRect.right = offScreenTestRect.left + 1;
-        offScreenTestRect.bottom = offScreenTestRect.top + 1;
-
-        bool isTitlebarIntersectWithMonitors = false;
-        EnumDisplayMonitors(
-            nullptr, &offScreenTestRect, [](HMONITOR, HDC, LPRECT, LPARAM lParam) -> BOOL {
-                auto intersectWithMonitor = reinterpret_cast<bool*>(lParam);
-                *intersectWithMonitor = true;
-                // Continue the enumeration
-                return FALSE;
-            },
-            reinterpret_cast<LPARAM>(&isTitlebarIntersectWithMonitors));
-
-        if (!isTitlebarIntersectWithMonitors)
-        {
-            // If the title bar is out-of-screen, we set the initial position to
-            // the top left corner of the nearest monitor
-            proposedRect.left = monitorInfo.rcWork.left;
-            proposedRect.top = monitorInfo.rcWork.top;
-        }
+        // If the title bar is out-of-screen, we set the initial position to
+        // the top left corner of the nearest monitor
+        proposedRect.left = monitorInfo.rcWork.left;
+        proposedRect.top = monitorInfo.rcWork.top;
+    }
 
-        auto initialSize = _logic.GetLaunchDimensions(dpix);
+    auto initialSize = _logic.GetLaunchDimensions(dpix);
 
-        const short islandWidth = Utils::ClampToShortMax(
-            static_cast<long>(ceil(initialSize.X)), 1);
-        const short islandHeight = Utils::ClampToShortMax(
-            static_cast<long>(ceil(initialSize.Y)), 1);
+    const short islandWidth = Utils::ClampToShortMax(
+        static_cast<long>(ceil(initialSize.X)), 1);
+    const short islandHeight = Utils::ClampToShortMax(
+        static_cast<long>(ceil(initialSize.Y)), 1);
 
-        // Get the size of a window we'd need to host that client rect. This will
-        // add the titlebar space.
-        const auto nonClientSize = _window->GetTotalNonClientExclusiveSize(dpix);
-        adjustedWidth = islandWidth + nonClientSize.cx;
-        adjustedHeight = islandHeight + nonClientSize.cy;
-    }
+    // Get the size of a window we'd need to host that client rect. This will
+    // add the titlebar space.
+    const auto nonClientSize = _window->GetTotalNonClientExclusiveSize(dpix);
+    adjustedWidth = islandWidth + nonClientSize.cx;
+    adjustedHeight = islandHeight + nonClientSize.cy;
 
     const COORD origin{ gsl::narrow<short>(proposedRect.left),
                         gsl::narrow<short>(proposedRect.top) };

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -143,6 +143,7 @@ void IslandWindow::_HandleCreateWindow(const WPARAM, const LPARAM lParam) noexce
     }
 
     ShowWindow(_window.get(), nCmdShow);
+
     UpdateWindow(_window.get());
 }
 

src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp

@@ -838,7 +838,10 @@ void NonClientIslandWindow::OnApplicationThemeChanged(const ElementTheme& reques
 void NonClientIslandWindow::_SetIsFullscreen(const bool fullscreenEnabled)
 {
     IslandWindow::_SetIsFullscreen(fullscreenEnabled);
-    _titlebar.Visibility(!fullscreenEnabled ? Visibility::Visible : Visibility::Collapsed);
+    if (_titlebar)
+    {
+        _titlebar.Visibility(!fullscreenEnabled ? Visibility::Visible : Visibility::Collapsed);
+    }
     // GH#4224 - When the auto-hide taskbar setting is enabled, then we don't
     // always get another window message to trigger us to remove the drag bar.
     // So, make sure to update the size of the drag region here, so that it