Implement z-index for windows and ensure correct stacking order on interaction

UI/GUI/Rendering/CanvasRenderSource.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Drawing;
 using System.Collections.Generic;
+using System.Linq;
 using Cosmos.Kernel.System.Graphics;
 
 namespace RemSox.UI.GUI.Rendering;
@@ -9,11 +10,20 @@ public sealed class CanvasRenderSource : IRenderSource
 {
     private static readonly Dictionary<int, Canvas> windowCanvases = new();
     private static readonly Dictionary<int, Point> windowPositions = new();
+    private static readonly Dictionary<int, int> windowZIndices = new();
 
     public void Render(IEnumerable<RenderCommand> commands)
     {
         foreach (RenderCommand command in commands)
         {
+            if (command.ElementType == "Window" || command.ElementType == "WindowMove")
+            {
+                if (command.Properties.TryGetValue("ZIndex", out object? rawZIndex) && rawZIndex is int z)
+                {
+                    windowZIndices[command.WindowId] = z;
+                }
+            }
+
             if (command.ElementType == "Window")
             {
                 Size size = command.Properties.TryGetValue("Size", out object? rawSize) && rawSize is Size windowSize
@@ -59,11 +69,11 @@ public sealed class CanvasRenderSource : IRenderSource
     {
         screenCanvas.Clear(Color.Black);
 
-        foreach (var kvp in windowPositions)
+        var orderedWindows = windowPositions.Keys.OrderBy(id => windowZIndices.TryGetValue(id, out int z) ? z : 0);
+
+        foreach (var windowId in orderedWindows)
         {
-            int windowId = kvp.Key;
-            Point position = kvp.Value;
-            if (windowCanvases.TryGetValue(windowId, out Canvas? windowCanvas))
+            if (windowPositions.TryGetValue(windowId, out Point position) && windowCanvases.TryGetValue(windowId, out Canvas? windowCanvas))
             {
                 screenCanvas.DrawCanvas(windowCanvas, position.X, position.Y);
             }

UI/GUI/Windows/Window.cs

@@ -14,6 +14,8 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
 
     public string Title { get; set; } = title;
 
+    public int ZIndex { get; set; }
+
     public bool AutoFlush { get; set; } = false;
 
     public bool IsFocused
@@ -51,6 +53,7 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
     private Size lastRenderedSize = new Size(-1, -1);
     private bool lastRenderedIsFocused = false;
     private string lastRenderedTitle = string.Empty;
+    private int lastRenderedZIndex = -1;
     private bool isFirstRender = true;
 
     public T CreateUIElement<T>(Action<T>? options = null) where T : UIElement, new()
@@ -92,6 +95,7 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
         bool windowStateChanged = isFirstRender || Size != lastRenderedSize || IsFocused != lastRenderedIsFocused || Title != lastRenderedTitle;
         bool anyChildChanged = uiElements.Values.Any(e => e.AnyPropertyChanged);
         bool positionChanged = Position != lastRenderedPosition;
+        bool zIndexChanged = ZIndex != lastRenderedZIndex;
 
         bool fullRedraw = windowStateChanged || anyChildChanged;
 
@@ -111,7 +115,8 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
                     [nameof(Size)] = Size,
                     [nameof(IsFocused)] = IsFocused,
                     [nameof(IsResizable)] = IsResizable,
-                    [nameof(IsDraggable)] = IsDraggable
+                    [nameof(IsDraggable)] = IsDraggable,
+                    [nameof(ZIndex)] = ZIndex
                 }
             });
 
@@ -128,7 +133,7 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
                 element.ClearChangedProperties();
             }
         }
-        else if (positionChanged)
+        else if (positionChanged || zIndexChanged)
         {
             commands.Add(new RenderCommand
             {
@@ -136,7 +141,10 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
                 ElementId = Id,
                 ElementType = "WindowMove",
                 Position = Position,
-                Properties = new Dictionary<string, object?>()
+                Properties = new Dictionary<string, object?>
+                {
+                    [nameof(ZIndex)] = ZIndex
+                }
             });
         }
 
@@ -147,6 +155,7 @@ public sealed class Window(string title, int processId, int id, IRenderSource re
             lastRenderedSize = Size;
             lastRenderedIsFocused = IsFocused;
             lastRenderedTitle = Title;
+            lastRenderedZIndex = ZIndex;
             isFirstRender = false;
         }
     }

UI/GUI/Windows/WindowManager.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.Drawing;
+using System.Linq;
 using RemSox.Processing;
 using RemSox.UI.GUI.Rendering;
 
@@ -12,6 +14,7 @@ public static class WindowManager
     private static readonly ConcurrentDictionary<int, List<Window>> windows = new();
 
     private static int nextWindowId = 1;
+    private static int nextZIndex = 1;
 
     private static Window? focusedWindow;
 
@@ -26,7 +29,8 @@ public static class WindowManager
         Window window = new(title, process.Id, GetNextWindowId(), renderSource)
         {
             Position = position,
-            Size = size
+            Size = size,
+            ZIndex = nextZIndex++
         };
 
         if (!windows.ContainsKey(process.Id))
@@ -69,6 +73,11 @@ public static class WindowManager
             return;
         }
 
+        if (window != null)
+        {
+            window.ZIndex = nextZIndex++;
+        }
+
         Window? previousFocusedWindow = focusedWindow;
         focusedWindow = window;
 
@@ -81,6 +90,19 @@ public static class WindowManager
         return focusedWindow == window;
     }
 
+    public static Window? TryBeginInteract(Point pointerPosition)
+    {
+        var allWindows = windows.Values.SelectMany(w => w).OrderByDescending(w => w.ZIndex);
+        foreach (var window in allWindows)
+        {
+            if (window.TryBeginInteract(pointerPosition))
+            {
+                return window;
+            }
+        }
+        return null;
+    }
+
     private static int GetNextWindowId()
     {
         return nextWindowId++;