fix(portals): add BufferOrigin to prevent submenu Y-clipping at desktop bottom

Portal submenus near the bottom of the screen were clipped because the
buffer coordinate system had no room above the portal. Add BufferOrigin
property (defaults to Bounds.Location for zero behavior change) that
lets the Start Menu map buffer (0,0) to the desktop top-left, giving
submenus space to shift upward. Update all buffer-to-screen mappings
in RenderCoordinator, HitTest, and CalculateDropdownBounds to use
BufferOrigin instead of Bounds for coordinate translation.

Author: nickprotop

SharpConsoleUI/Controls/MenuControl/MenuControl.DropdownManagement.cs

@@ -220,16 +220,17 @@ private Rectangle CalculateDropdownBounds(MenuItem item)
         }
         else if (Container is Core.DesktopPortalContainer dpc)
         {
-            // Desktop portal context — clamp to available screen space from portal origin.
-            // Buffer pos (bx, by) → screen pos (Bounds.X+bx, Bounds.Y+by).
-            // Rendering clips to desktopBottomRight — use the same reference point.
+            // Desktop portal context — clamp to available screen space in buffer coordinates.
+            // Item bounds are in buffer space (layout positions relative to buffer origin).
+            // Using BufferOrigin (instead of Bounds) ensures the range covers the full buffer,
+            // allowing submenus to use space above the portal when BufferOrigin < Bounds.Y.
             var ws = Container.GetConsoleWindowSystem!;
             var desktopBR = ws.DesktopBottomRight;
-            var portalScreenX = dpc.Portal.Bounds.X;
-            var portalScreenY = dpc.Portal.Bounds.Y;
+            var originX = dpc.Portal.BufferOrigin.X;
+            var originY = dpc.Portal.BufferOrigin.Y;
             screenBounds = new Rectangle(0, 0,
-                desktopBR.X + 1 - portalScreenX,
-                desktopBR.Y + 1 - portalScreenY);
+                desktopBR.X + 1 - originX,
+                desktopBR.Y + 1 - originY);
         }
         else
         {

SharpConsoleUI/Core/DesktopPortal.cs

@@ -22,6 +22,8 @@ namespace SharpConsoleUI.Core
 	/// <param name="DimBackground">Whether to dim the screen behind the portal.</param>
 	/// <param name="OnDismiss">Callback invoked when the portal is dismissed.</param>
 	/// <param name="Owner">The control that owns this portal (for identification/cleanup).</param>
+	/// <param name="BufferSize">Buffer size for rendering. Defaults to Bounds size.</param>
+	/// <param name="BufferOrigin">Screen coordinate that buffer (0,0) maps to. Defaults to Bounds.Location.</param>
 	public record DesktopPortalOptions(
 		IWindowControl Content,
 		Rectangle Bounds,
@@ -30,7 +32,8 @@ public record DesktopPortalOptions(
 		bool DimBackground = false,
 		Action? OnDismiss = null,
 		IWindowControl? Owner = null,
-		Size? BufferSize = null
+		Size? BufferSize = null,
+		Point? BufferOrigin = null
 	);
 
 	/// <summary>
@@ -72,6 +75,13 @@ public class DesktopPortal
 		/// </summary>
 		public Size BufferSize { get; }
 
+		/// <summary>
+		/// Screen coordinate that buffer position (0,0) maps to.
+		/// Defaults to Bounds.Location for backwards compatibility.
+		/// Set to DesktopUpperLeft when the buffer needs to cover space above the portal (e.g., Start Menu).
+		/// </summary>
+		public Point BufferOrigin { get; }
+
 		/// <summary>Stacking order among portals (higher = on top).</summary>
 		public int ZOrder { get; }
 
@@ -117,6 +127,7 @@ internal DesktopPortal(DesktopPortalOptions options, int zOrder, ConsoleWindowSy
 			IsDirty = true;
 			CreatedAt = DateTime.Now;
 			BufferSize = options.BufferSize ?? new Size(Bounds.Width, Bounds.Height);
+			BufferOrigin = options.BufferOrigin ?? new Point(Bounds.X, Bounds.Y);
 
 			Container = new DesktopPortalContainer(this);
 
@@ -131,7 +142,9 @@ internal DesktopPortal(DesktopPortalOptions options, int zOrder, ConsoleWindowSy
 
 			// Arrange at portal bounds so the root control fills the declared area.
 			// Controls that want to be smaller will respect their own sizing within this rect.
-			RootNode.Arrange(new LayoutRect(0, 0, Bounds.Width, Bounds.Height));
+			int rootOffsetX = Bounds.X - BufferOrigin.X;
+			int rootOffsetY = Bounds.Y - BufferOrigin.Y;
+			RootNode.Arrange(new LayoutRect(rootOffsetX, rootOffsetY, Bounds.Width, Bounds.Height));
 
 			// Compute initial control bounds for hit-testing before first render
 			RootNode.Visit(node =>

SharpConsoleUI/Core/DesktopPortalService.cs

@@ -184,8 +184,8 @@ public bool AnyPortalDirty()
 				// Check against control bounds, not full portal bounds
 				foreach (var bounds in portal.ControlBounds)
 				{
-					int screenX = portal.Bounds.X + bounds.X;
-					int screenY = portal.Bounds.Y + bounds.Y;
+					int screenX = portal.BufferOrigin.X + bounds.X;
+					int screenY = portal.BufferOrigin.Y + bounds.Y;
 					var screenRect = new Rectangle(screenX, screenY, bounds.Width, bounds.Height);
 					if (screenRect.Contains(point))
 						return portal;

SharpConsoleUI/Dialogs/StartMenuDialog.cs

@@ -118,7 +118,8 @@ public static void Show(ConsoleWindowSystem windowSystem)
 			ConsumeClickOnDismiss: true,
 			DimBackground: false,
 			Owner: menu,
-			BufferSize: new Size(desktopDims.Width, desktopDims.Height)));
+			BufferSize: new Size(desktopDims.Width, desktopDims.Height),
+			BufferOrigin: new Point(desktopUpperLeft.X, desktopUpperLeft.Y)));
 	}
 
 	private static void BuildSystemCategory(MenuBuilder menuBuilder, ConsoleWindowSystem windowSystem)

SharpConsoleUI/Rendering/RenderCoordinator.cs

@@ -176,8 +176,8 @@ public void RestorePortalRegions(Core.DesktopPortal portal)
 			foreach (var bounds in portal.ControlBounds)
 			{
 				var screenRect = new Rectangle(
-					portal.Bounds.X + bounds.X,
-					portal.Bounds.Y + bounds.Y,
+					portal.BufferOrigin.X + bounds.X,
+					portal.BufferOrigin.Y + bounds.Y,
 					bounds.Width,
 					bounds.Height);
 				RestoreScreenRegion(screenRect, belowPortal: portal);
@@ -429,8 +429,8 @@ private void RestoreScreenRegion(Rectangle screenRect, Core.DesktopPortal? below
 
 				foreach (var bounds in portal.ControlBounds)
 				{
-					int portalScreenX = portal.Bounds.X + bounds.X;
-					int portalScreenY = portal.Bounds.Y + bounds.Y;
+					int portalScreenX = portal.BufferOrigin.X + bounds.X;
+					int portalScreenY = portal.BufferOrigin.Y + bounds.Y;
 					var portalScreenRect = new Rectangle(portalScreenX, portalScreenY, bounds.Width, bounds.Height);
 
 					if (!portalScreenRect.IntersectsWith(clippedRect))
@@ -500,7 +500,9 @@ private void RenderDesktopPortals()
 				// Arrange at portal bounds so root control fills the declared area
 				var constraints = Layout.LayoutConstraints.Loose(bufSize.Width, bufSize.Height);
 				portal.RootNode.Measure(constraints);
-				portal.RootNode.Arrange(new Layout.LayoutRect(0, 0, portal.Bounds.Width, portal.Bounds.Height));
+				int rootOffX = portal.Bounds.X - portal.BufferOrigin.X;
+				int rootOffY = portal.Bounds.Y - portal.BufferOrigin.Y;
+				portal.RootNode.Arrange(new Layout.LayoutRect(rootOffX, rootOffY, portal.Bounds.Width, portal.Bounds.Height));
 
 				// Paint DOM to buffer (clip to full buffer so submenus can render beyond content bounds)
 				var clipRect = new Layout.LayoutRect(0, 0, bufSize.Width, bufSize.Height);
@@ -560,8 +562,8 @@ private void RestorePortalDelta(Core.DesktopPortal portal, List<Layout.LayoutRec
 				{
 					// Convert to screen space and restore
 					var screenRect = new Rectangle(
-						portal.Bounds.X + prevRect.X,
-						portal.Bounds.Y + prevRect.Y,
+						portal.BufferOrigin.X + prevRect.X,
+						portal.BufferOrigin.Y + prevRect.Y,
 						prevRect.Width,
 						prevRect.Height);
 					RestoreScreenRegion(screenRect, belowPortal: portal);
@@ -583,8 +585,8 @@ private void WritePortalControlRegions(Core.DesktopPortal portal)
 
 			foreach (var bounds in portal.ControlBounds)
 			{
-				int screenX = portal.Bounds.X + bounds.X;
-				int screenY = portal.Bounds.Y + bounds.Y;
+				int screenX = portal.BufferOrigin.X + bounds.X;
+				int screenY = portal.BufferOrigin.Y + bounds.Y;
 
 				// Clip to desktop area
 				int clipLeft = Math.Max(screenX, desktopUpperLeft.X);