feat: Native GTK4 modal dialog windows for PushModalAsync

BACKEND_IMPLEMENTATION_CHECKLIST.MD

@@ -43,7 +43,7 @@ Implementation status of the .NET MAUI backend for Linux using GTK4. Adapted fro
 | Control | Status | Notes |
 |---------|--------|-------|
 | ✅ **Application** | Done | App lifecycle via `GtkMauiApplication`, `Gtk.Application` integration |
-| ✅ **Window** | Done | Title, Width/Height mapping, default size 1024×768, min 800×600, Activated/Deactivated events, modal push/pop. X/Y positioning disabled (Wayland/X11 compositor constraints) |
+| ✅ **Window** | Done | Title, Width/Height mapping, default size 1024×768, min 800×600, Activated/Deactivated events, native modal dialog windows via `PushModalAsync` with sizing options (`GtkPage` attached properties). X/Y positioning disabled (Wayland/X11 compositor constraints) |
 | ✅ **Multi-Window** | Done | `Application.OpenWindow`/`CloseWindow`, `Application.Windows` collection tracking, window lifecycle events (Creating, Destroying, Activated, Deactivated) |
 
 ---
@@ -144,7 +144,7 @@ Implementation status of the .NET MAUI backend for Linux using GTK4. Adapted fro
 | ✅ **DisplayAlert** | Done | Custom GTK Window dialog with Title, message, accept/cancel buttons |
 | ✅ **DisplayActionSheet** | Done | Dialog with action buttons, destructive button styling, cancel |
 | ✅ **DisplayPromptAsync** | Done | Text entry dialog with placeholder, initial value, validation |
-| ✅ **Modal overlay** | Done | GTK modal window with transient-for parent |
+| ✅ **Modal Pages** | Done | `PushModalAsync` uses native GTK4 modal `Gtk.Window` (default). `GtkPage` attached properties: `ModalPresentationStyle` (Dialog/Inline), `ModalSizesToContent`, `ModalWidth`/`ModalHeight`, `ModalMinWidth`/`ModalMinHeight` |
 
 ---
 

README.md

@@ -60,6 +60,7 @@ https://github.com/user-attachments/assets/70f2a910-94b3-437c-945a-6b71223c5cd3
 - **Font icons** — Embedded font registration with fontconfig/Pango, FontImageSource rendering via Cairo. FontAwesome and custom icon fonts work out of the box.
 - **FormattedText** — Rich text via Pango markup: Span colors, fonts, sizes, bold/italic, underline/strikethrough, character spacing.
 - **Alerts & Dialogs** — `DisplayAlert`, `DisplayActionSheet`, `DisplayPromptAsync` via native GTK4 modal windows.
+- **Modal Pages** — `PushModalAsync` presents pages as native GTK4 dialog windows by default, with attached properties for custom sizing, content-fit sizing, and inline (legacy) presentation via `GtkPage`.
 - **Brushes & Gradients** — SolidColorBrush, LinearGradientBrush, RadialGradientBrush via CSS gradients.
 - **Tooltips & Context Menus** — `ToolTipProperties.Text` and `ContextFlyout` via `Gtk.PopoverMenu`.
 - **Theming** — Automatic light/dark theme detection via `GtkThemeManager`.
@@ -85,7 +86,7 @@ https://github.com/user-attachments/assets/70f2a910-94b3-437c-945a-6b71223c5cd3
 | Input Controls | 100% | Picker, DatePicker, TimePicker, SearchBar |
 | Collection Controls | 100% | Virtualized CollectionView, ListView, TableView, CarouselView, SwipeView |
 | Navigation & Routing | 100% | Push/pop, Shell routes, query parameters |
-| Alerts & Dialogs | 100% | All three dialog types + modal overlay |
+| Alerts & Dialogs | 100% | All three dialog types + native modal dialog windows |
 | Gesture Recognizers | 100% | All 5 gesture types |
 | Graphics & Shapes | 100% | GraphicsView + all 6 shape types |
 | Font Management | 100% | Registrar, manager, FontImageSource, named sizes |

samples/Platform.Maui.Linux.Gtk4.Sample/App.cs

@@ -46,6 +46,7 @@ private readonly (string name, Func<Page> factory)[] _pages =
 		("📂 FlyoutPage", () => new FlyoutPageDemo()),
 		("🐚 Shell Navigation", () => new ShellDemoPage()),
 		("🧬 ControlTemplate", () => new ControlTemplatePage()),
+		("🪟 Modal Pages", () => new ModalDemoPage()),
 		("🪟 Multi-Window", () => new MultiWindowPage()),
 		("🎨 Theme", () => new ThemePage()),
 	];

samples/Platform.Maui.Linux.Gtk4.Sample/Pages/ModalDemoPage.cs

@@ -0,0 +1,225 @@
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Graphics;
+using Platform.Maui.Linux.Gtk4.Platform;
+
+namespace Platform.Maui.Linux.Gtk4.Sample.Pages;
+
+/// <summary>
+/// Demonstrates PushModalAsync with native GTK4 dialog windows (default),
+/// custom sizing, content-sized dialogs, and the inline fallback.
+/// </summary>
+class ModalDemoPage : ContentPage
+{
+	private readonly Label _statusLabel;
+
+	public ModalDemoPage()
+	{
+		Title = "Modal Pages";
+
+		_statusLabel = new Label
+		{
+			Text = "Tap a button to push a modal page.",
+			HorizontalOptions = LayoutOptions.Center,
+			Margin = new Thickness(0, 0, 0, 20),
+		};
+
+		// --- Default (full-size dialog) ---
+		var nativeModalBtn = new Button
+		{
+			Text = "Dialog Modal (Default)",
+			AutomationId = "btnNativeModal",
+			Margin = new Thickness(0, 4),
+		};
+		nativeModalBtn.Clicked += async (s, e) =>
+		{
+			var modal = CreateModalContent("Default Dialog",
+				"Full-size native GTK4 modal window.\n"
+				+ "Matches the parent window dimensions.");
+			await Navigation.PushModalAsync(modal);
+			_statusLabel.Text = "Default dialog was dismissed.";
+		};
+
+		// --- Custom size (400×300) ---
+		var customSizeBtn = new Button
+		{
+			Text = "Dialog Modal (400×300)",
+			AutomationId = "btnCustomSize",
+			Margin = new Thickness(0, 4),
+		};
+		customSizeBtn.Clicked += async (s, e) =>
+		{
+			var modal = CreateModalContent("Small Dialog",
+				"Custom sized dialog (400×300).\nResizable with min constraints.");
+			GtkPage.SetModalWidth(modal, 400);
+			GtkPage.SetModalHeight(modal, 300);
+			GtkPage.SetModalMinWidth(modal, 300);
+			GtkPage.SetModalMinHeight(modal, 200);
+			await Navigation.PushModalAsync(modal);
+			_statusLabel.Text = "Custom size dialog was dismissed.";
+		};
+
+		// --- Sizes to content ---
+		var contentSizeBtn = new Button
+		{
+			Text = "Dialog Modal (Sizes to Content)",
+			AutomationId = "btnContentSize",
+			Margin = new Thickness(0, 4),
+		};
+		contentSizeBtn.Clicked += async (s, e) =>
+		{
+			var modal = CreateModalContent("Content-Sized",
+				"This dialog measured its content\nand sized itself to fit.");
+			GtkPage.SetModalSizesToContent(modal, true);
+			GtkPage.SetModalMinWidth(modal, 250);
+			GtkPage.SetModalMinHeight(modal, 150);
+			await Navigation.PushModalAsync(modal);
+			_statusLabel.Text = "Content-sized dialog was dismissed.";
+		};
+
+		// --- Inline (legacy) ---
+		var inlineModalBtn = new Button
+		{
+			Text = "Inline Modal (Legacy)",
+			AutomationId = "btnInlineModal",
+			Margin = new Thickness(0, 4),
+		};
+		inlineModalBtn.Clicked += async (s, e) =>
+		{
+			var modal = CreateModalContent("Inline Modal",
+				"Inline presentation style.\n"
+				+ "Hides current content and shows\nthe modal in its place.");
+			GtkPage.SetModalPresentationStyle(modal, GtkModalPresentationStyle.Inline);
+			await Navigation.PushModalAsync(modal);
+			_statusLabel.Text = "Inline modal was dismissed.";
+		};
+
+		// --- Stacked ---
+		var stackedModalBtn = new Button
+		{
+			Text = "Push Two Stacked Modals",
+			AutomationId = "btnStackedModal",
+			Margin = new Thickness(0, 4),
+		};
+		stackedModalBtn.Clicked += async (s, e) =>
+		{
+			var first = CreateModalContent("First Modal",
+				"This is the first modal dialog.\n"
+				+ "Tap 'Push Another' to stack a second modal.");
+
+			var pushAnotherBtn = new Button
+			{
+				Text = "Push Another Modal",
+				AutomationId = "btnPushAnother",
+				BackgroundColor = Colors.DarkSlateBlue,
+				TextColor = Colors.White,
+				Margin = new Thickness(0, 8),
+			};
+			pushAnotherBtn.Clicked += async (s2, e2) =>
+			{
+				var second = CreateModalContent("Second Modal",
+					"Stacked modal dialog.\nDismiss to return to the first.");
+				GtkPage.SetModalWidth(second, 400);
+				GtkPage.SetModalHeight(second, 300);
+				await Navigation.PushModalAsync(second);
+			};
+
+			if (first.Content is VerticalStackLayout vsl)
+				vsl.Children.Insert(vsl.Children.Count - 1, pushAnotherBtn);
+
+			await Navigation.PushModalAsync(first);
+			_statusLabel.Text = "Stacked modals were dismissed.";
+		};
+
+		Content = new ScrollView
+		{
+			Content = new VerticalStackLayout
+			{
+				Padding = new Thickness(20),
+				Spacing = 8,
+				Children =
+				{
+					new Label
+					{
+						Text = "Modal Pages Demo",
+						FontSize = 22,
+						FontAttributes = FontAttributes.Bold,
+						Margin = new Thickness(0, 0, 0, 8),
+					},
+					_statusLabel,
+
+					new Label { Text = "Dialog Presentations", FontSize = 16, FontAttributes = FontAttributes.Bold, TextColor = Colors.CornflowerBlue },
+					nativeModalBtn,
+					customSizeBtn,
+					contentSizeBtn,
+
+					new Border { HeightRequest = 1, BackgroundColor = Colors.Gray, Opacity = 0.3, StrokeThickness = 0 },
+
+					new Label { Text = "Other Styles", FontSize = 16, FontAttributes = FontAttributes.Bold, TextColor = Colors.CornflowerBlue },
+					inlineModalBtn,
+					stackedModalBtn,
+
+					new Border { HeightRequest = 1, BackgroundColor = Colors.Gray, Opacity = 0.3, StrokeThickness = 0 },
+
+					new Label
+					{
+						Text = "• Default opens a full-size native GTK4 dialog\n"
+							+ "• Custom size sets explicit dialog dimensions\n"
+							+ "• Content-sized measures the MAUI content\n"
+							+ "• Inline uses the legacy in-window overlay",
+						FontSize = 12,
+						TextColor = Colors.Gray,
+					},
+				}
+			}
+		};
+	}
+
+	private static ContentPage CreateModalContent(string title, string description)
+	{
+		var dismissBtn = new Button
+		{
+			Text = "Dismiss",
+			AutomationId = "btnDismissModal",
+			BackgroundColor = Colors.Tomato,
+			TextColor = Colors.White,
+			Margin = new Thickness(0, 16),
+		};
+
+		var page = new ContentPage
+		{
+			Title = title,
+			BackgroundColor = Color.FromArgb("#F5F5F5"),
+			Content = new VerticalStackLayout
+			{
+				Padding = new Thickness(30),
+				Spacing = 12,
+				VerticalOptions = LayoutOptions.Center,
+				Children =
+				{
+					new Label
+					{
+						Text = title,
+						FontSize = 24,
+						FontAttributes = FontAttributes.Bold,
+						HorizontalOptions = LayoutOptions.Center,
+					},
+					new Label
+					{
+						Text = description,
+						FontSize = 14,
+						HorizontalOptions = LayoutOptions.Center,
+						HorizontalTextAlignment = TextAlignment.Center,
+					},
+					dismissBtn,
+				}
+			}
+		};
+
+		dismissBtn.Clicked += async (s, e) =>
+		{
+			await page.Navigation.PopModalAsync();
+		};
+
+		return page;
+	}
+}