Create a separate InputSystem for each OS-level window.

Also, we now have to tell each ImGui which InputSystem it should talk to.

Yafc.Model/Blueprints/Blueprint.cs

@@ -14,7 +14,7 @@ public class BlueprintString(string blueprintName) {
         private static readonly byte[] header = { 0x78, 0xDA };
 
         public string ToBpString() {
-            if (InputSystem.Instance.control) {
+            if (Ui.ActiveInputSystem?.control ?? false) {
                 return ToJson();
             }
 

Yafc.Model/Serialization/UndoSystem.cs

@@ -57,8 +57,10 @@ private static void MakeUndoBatch(object? state) {
         }
 
         private void Schedule() {
-            InputSystem.Instance.DispatchOnGestureFinish(MakeUndoBatch, this);
-            scheduled = true;
+            if (Ui.ActiveInputSystem != null) {
+                Ui.ActiveInputSystem.DispatchOnGestureFinish(MakeUndoBatch, this);
+                scheduled = true;
+            }
         }
 
         public void Suspend() {

Yafc.UI/Core/InputSystem.cs

@@ -17,10 +17,6 @@ public interface IMouseFocus {
     }
 
     public sealed class InputSystem {
-        public static readonly InputSystem Instance = new InputSystem();
-
-        private InputSystem() { }
-
         public Window? mouseOverWindow { get; private set; }
         private IPanel? hoveringPanel;
         private IPanel? mouseDownPanel;

Yafc.UI/Core/Ui.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Diagnostics;
+using System.Linq;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
@@ -34,6 +36,15 @@ public static void Start() {
             mainThreadId = Thread.CurrentThread.ManagedThreadId;
         }
 
+        /// <summary>
+        /// The <see cref="InputSystem"/> belonging to the active window, if such a window exists. Failing that, it is the input system for the only window,
+        /// if there is exactly one window. This is the *current* active input system, and may be about to change if a new (OS-level) window is being
+        /// constructed or if the focus is changing. For this reason, try to get your InputSystem from a source that reflects the new value,
+        /// rather than the current value.
+        /// </summary>
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public static InputSystem? ActiveInputSystem => windows.Values.FirstOrDefault(w => w.active)?.InputSystem ?? (windows.Count == 1 ? windows.Values.First().InputSystem : null);
+
         public static long time { get; private set; }
         private static readonly Stopwatch timeWatch = Stopwatch.StartNew();
 
@@ -55,7 +66,8 @@ public static void MainLoop() {
 
         public static void ProcessEvents() {
             try {
-                var inputSystem = InputSystem.Instance;
+                InputSystem? inputSystem = ActiveInputSystem;
+                if (inputSystem == null) { return; }
                 long minNextEvent = long.MaxValue - 1;
                 foreach (var (_, window) in windows) {
                     minNextEvent = Math.Min(minNextEvent, window.nextRepaintTime);
@@ -123,18 +135,21 @@ public static void ProcessEvents() {
 
                             switch (evt.window.windowEvent) {
                                 case SDL.SDL_WindowEventID.SDL_WINDOWEVENT_ENTER:
-                                    inputSystem.MouseEnterWindow(window);
+                                    window.InputSystem.MouseEnterWindow(window);
                                     break;
                                 case SDL.SDL_WindowEventID.SDL_WINDOWEVENT_LEAVE:
-                                    inputSystem.MouseExitWindow(window);
+                                    window.InputSystem.MouseExitWindow(window);
                                     break;
                                 case SDL.SDL_WindowEventID.SDL_WINDOWEVENT_CLOSE:
                                     window.Close();
                                     break;
                                 case SDL.SDL_WindowEventID.SDL_WINDOWEVENT_FOCUS_LOST:
-                                    inputSystem.SetKeyboardFocus(null);
                                     window.FocusLost();
                                     break;
+                                case SDL.SDL_WindowEventID.SDL_WINDOWEVENT_FOCUS_GAINED:
+                                    window.FocusGained();
+                                    window.Rebuild();
+                                    break;
                                 case SDL.SDL_WindowEventID.SDL_WINDOWEVENT_MINIMIZED:
                                     window.Minimized();
                                     break;

Yafc.UI/Core/Window.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Diagnostics.CodeAnalysis;
 using System.Numerics;
 using SDL2;
 
@@ -14,6 +13,7 @@ public abstract class Window : IDisposable {
         internal bool repaintRequired = true;
         internal bool visible;
         internal bool closed;
+        internal bool active;
         internal long nextRepaintTime = long.MaxValue;
         internal float pixelsPerUnit;
         public virtual SchemeColor backgroundColor => SchemeColor.Background;
@@ -28,10 +28,13 @@ public abstract class Window : IDisposable {
         public int displayIndex => SDL.SDL_GetWindowDisplayIndex(window);
         public int repaintCount { get; private set; }
 
+        public InputSystem InputSystem { get; } = new();
+
         public Vector2 size => contentSize;
 
         public virtual bool preventQuit => false;
-        internal Window(Padding padding) => rootGui = new ImGui(Build, padding);
+
+        internal Window(Padding padding) => rootGui = new ImGui(Build, padding, InputSystem);
 
         internal void Create() {
             if (surface is null) { throw new InvalidOperationException($"surface must be set by a derived class before calling {nameof(Create)}."); }
@@ -142,6 +145,7 @@ public void Repaint() {
 
         protected internal virtual void Close() {
             visible = false;
+            active = false;
             closed = true;
             surface?.Dispose();
             SDL.SDL_DestroyWindow(window);
@@ -158,8 +162,8 @@ private void Focus() {
             }
         }
 
-
-        public virtual void FocusLost() { }
+        public virtual void FocusLost() => active = false;
+        public void FocusGained() => active = true;
         public virtual void Minimized() { }
 
         public void SetNextRepaint(long nextRepaintTime) {
@@ -174,7 +178,7 @@ public void ShowTooltip(Tooltip tooltip) {
         }
 
         public void ShowTooltip(ImGui targetGui, Rect target, GuiBuilder builder, float width = 20f) {
-            simpleTooltip ??= new SimpleTooltip();
+            simpleTooltip ??= new SimpleTooltip(InputSystem);
             simpleTooltip.Show(builder, targetGui, target, width);
             ShowTooltip(simpleTooltip);
 
@@ -186,7 +190,7 @@ public void ShowDropDown(DropDownPanel dropDown) {
         }
 
         public void ShowDropDown(ImGui targetGui, Rect target, GuiBuilder builder, Padding padding, float width = 20f) {
-            simpleDropDown ??= new SimpleDropDown();
+            simpleDropDown ??= new SimpleDropDown(InputSystem);
             simpleDropDown.SetPadding(padding);
             simpleDropDown.SetFocus(targetGui, target, builder, width);
             ShowDropDown(simpleDropDown);
@@ -216,6 +220,6 @@ private void Build(ImGui gui) {
         protected abstract void BuildContents(ImGui gui);
         public virtual void Dispose() => rootGui.Dispose();
 
-        internal ImGui.DragOverlay GetDragOverlay() => draggingOverlay ??= new ImGui.DragOverlay();
+        internal ImGui.DragOverlay GetDragOverlay() => draggingOverlay ??= new ImGui.DragOverlay(InputSystem);
     }
 }

Yafc.UI/ImGui/DropDownPanel.cs

@@ -9,8 +9,8 @@ public abstract class AttachedPanel {
         protected float width;
         protected virtual SchemeColor background => SchemeColor.PureBackground;
 
-        protected AttachedPanel(Padding padding, float width) {
-            contents = new ImGui(BuildContents, padding) { boxColor = background, boxShadow = RectangleBorder.Thin };
+        protected AttachedPanel(Padding padding, float width, InputSystem inputSystem) {
+            contents = new ImGui(BuildContents, padding, inputSystem) { boxColor = background, boxShadow = RectangleBorder.Thin };
             this.width = width;
         }
 
@@ -49,13 +49,13 @@ public void Build(ImGui gui) {
         protected abstract void BuildContents(ImGui gui);
     }
 
-    public abstract class DropDownPanel : AttachedPanel, IMouseFocus {
+    public abstract class DropDownPanel(Padding padding, float width, InputSystem inputSystem) : AttachedPanel(padding, width, inputSystem), IMouseFocus {
         private bool focused;
-        protected DropDownPanel(Padding padding, float width) : base(padding, width) { }
+
         protected override bool ShouldBuild(ImGui source, Rect sourceRect, ImGui parent, Rect parentRect) => focused;
 
         public override void SetFocus(ImGui source, Rect rect) {
-            InputSystem.Instance.SetMouseFocus(this);
+            source.inputSystem.SetMouseFocus(this);
             base.SetFocus(source, rect);
         }
 
@@ -80,7 +80,7 @@ public void FocusChanged(bool focused) {
     public class SimpleDropDown : DropDownPanel {
         private GuiBuilder? builder;
 
-        public SimpleDropDown() : base(new Padding(1f), 20f) => contents.AddMessageHandler<ImGuiUtils.CloseDropdownEvent>(HandleDropdownClosed);
+        public SimpleDropDown(InputSystem inputSystem) : base(new Padding(1f), 20f, inputSystem) => contents.AddMessageHandler<ImGuiUtils.CloseDropdownEvent>(HandleDropdownClosed);
 
         private bool HandleDropdownClosed(ImGuiUtils.CloseDropdownEvent _) {
             Close();
@@ -118,10 +118,15 @@ protected override void BuildContents(ImGui gui) {
     }
 
     public abstract class Tooltip : AttachedPanel {
-        protected Tooltip(Padding padding, float width) : base(padding, width) => contents.mouseCapture = false;
+        private readonly InputSystem inputSystem;
+        protected Tooltip(Padding padding, float width, InputSystem inputSystem) : base(padding, width, inputSystem) {
+            contents.mouseCapture = false;
+            this.inputSystem = inputSystem;
+        }
+
         protected override bool ShouldBuild(ImGui source, Rect sourceRect, ImGui parent, Rect parentRect) {
             var window = source.window;
-            if (InputSystem.Instance.mouseOverWindow != window) {
+            if (inputSystem.mouseOverWindow != window) {
                 return false;
             }
 
@@ -143,16 +148,14 @@ protected override Vector2 CalculatePosition(ImGui gui, Rect targetRect, Vector2
         }
     }
 
-    public class SimpleTooltip : Tooltip {
+    public class SimpleTooltip(InputSystem inputSystem) : Tooltip(new Padding(0.5f), 30f, inputSystem) {
         private GuiBuilder? builder;
         public void Show(GuiBuilder builder, ImGui gui, Rect rect, float width = 30f) {
             this.width = width;
             this.builder = builder;
             base.SetFocus(gui, rect);
         }
 
-        public SimpleTooltip() : base(new Padding(0.5f), 30f) { }
-
         protected override void BuildContents(ImGui gui) {
             gui.boxColor = SchemeColor.PureBackground;
             gui.textColor = SchemeColor.BackgroundText;

Yafc.UI/ImGui/ImGui.cs

@@ -50,7 +50,7 @@ public enum RectAllocator {
     public delegate void GuiBuilder(ImGui gui);
 
     public sealed partial class ImGui : IDisposable, IPanel {
-        public ImGui(GuiBuilder? guiBuilder, Padding padding, RectAllocator defaultAllocator = RectAllocator.Stretch, bool clip = false) {
+        public ImGui(GuiBuilder? guiBuilder, Padding padding, InputSystem inputSystem, RectAllocator defaultAllocator = RectAllocator.Stretch, bool clip = false) {
             this.guiBuilder = guiBuilder;
             if (guiBuilder == null) {
                 action = ImGuiAction.Build;
@@ -59,6 +59,7 @@ public ImGui(GuiBuilder? guiBuilder, Padding padding, RectAllocator defaultAlloc
             this.defaultAllocator = defaultAllocator;
             this.clip = clip;
             initialPadding = padding;
+            this.inputSystem = inputSystem ?? throw new ArgumentNullException(nameof(inputSystem));
         }
 
         public readonly GuiBuilder? guiBuilder;
@@ -94,7 +95,7 @@ public Vector2 offset {
                 screenRect -= (_offset - value);
                 _offset = value;
                 if (mousePresent) {
-                    MouseMove(InputSystem.Instance.mouseDownButton);
+                    MouseMove(inputSystem.mouseDownButton);
                 }
                 else {
                     Repaint();

Yafc.UI/ImGui/ImGuiBuilding.cs

@@ -30,6 +30,7 @@ public void Deconstruct(out Rect rect, out T data, out SchemeColor color) {
         public SchemeColor boxColor { get; set; } = SchemeColor.None;
         public RectangleBorder boxShadow { get; set; } = RectangleBorder.None;
         public Padding initialPadding { get; set; }
+        internal readonly InputSystem inputSystem;
 
         public void DrawRectangle(Rect rect, SchemeColor color, RectangleBorder border = RectangleBorder.None) {
             if (action != ImGuiAction.Build) {
@@ -154,7 +155,7 @@ public void BuildIcon(Icon icon, float size = 1.5f, SchemeColor color = SchemeCo
             }
         }
 
-        public Vector2 mousePosition => InputSystem.Instance.mousePosition - screenRect.Position;
+        public Vector2 mousePosition => inputSystem.mousePosition - screenRect.Position;
         public bool mousePresent { get; private set; }
         public Rect mouseDownRect { get; private set; }
         public Rect mouseOverRect { get; private set; } = Rect.VeryBig;
@@ -348,7 +349,7 @@ public void SetFocus(Rect rect) {
         }
 
         public void SetTextInputFocus(Rect rect, string text) {
-            if (textInputHelper != null && InputSystem.Instance.currentKeyboardFocus != textInputHelper) {
+            if (textInputHelper != null && inputSystem.currentKeyboardFocus != textInputHelper) {
                 SetFocus(rect);
                 textInputHelper.SetFocus(rect, text);
             }

Yafc.UI/ImGui/ImGuiDrag.cs

@@ -65,14 +65,13 @@ public bool DoListReordering<T>(Rect moveHandle, Rect contents, T index, out T m
         }
 
 
-        internal class DragOverlay {
-            private readonly ImGui contents = new ImGui(null, default) { mouseCapture = false };
+        internal class DragOverlay(InputSystem inputSystem) {
+            private readonly ImGui contents = new ImGui(null, default, inputSystem) { mouseCapture = false };
 
             private ImGui? currentSource;
             private Vector2 mouseOffset;
             private Rect realPosition;
 
-
             public bool ShouldConsumeDrag(ImGui source, Vector2 point) => currentSource == source && realPosition.Contains(source.ToWindowPosition(point));
 
             private void ExtractDrawCommandsFrom<T>(List<DrawCommand<T>> sourceList, List<DrawCommand<T>> targetList, Rect rect) {
@@ -117,7 +116,7 @@ public void Build(ImGui screenGui) {
                     return;
                 }
 
-                if (InputSystem.Instance.mouseDownButton == -1) {
+                if (inputSystem.mouseDownButton == -1) {
                     currentSource = null;
                     realPosition = default;
                     return;
@@ -134,7 +133,7 @@ public void Build(ImGui screenGui) {
         }
 
         public bool ShouldEnterDrag(Rect moveHandle) {
-            if (action != ImGuiAction.MouseMove || !IsMouseDown(moveHandle) || isDragging || Vector2.DistanceSquared(InputSystem.Instance.mousePosition, InputSystem.Instance.mouseDownPosition) < 1f) {
+            if (action != ImGuiAction.MouseMove || !IsMouseDown(moveHandle) || isDragging || Vector2.DistanceSquared(inputSystem.mousePosition, inputSystem.mouseDownPosition) < 1f) {
                 return false;
             }
 

Yafc.UI/ImGui/ImGuiTextInputHelper.cs

@@ -30,7 +30,7 @@ public void SetFocus(Rect boundingRect, string setText) {
                 editHistory.Clear();
                 text = setText;
             }
-            InputSystem.Instance.SetKeyboardFocus(this);
+            gui.inputSystem.SetKeyboardFocus(this);
             rect = boundingRect;
             caret = selectionAnchor = setText.Length;
         }
@@ -251,7 +251,7 @@ public bool KeyDown(SDL.SDL_Keysym key) {
                 case SDL.SDL_Scancode.SDL_SCANCODE_RETURN2:
                 case SDL.SDL_Scancode.SDL_SCANCODE_KP_ENTER:
                 case SDL.SDL_Scancode.SDL_SCANCODE_ESCAPE:
-                    InputSystem.Instance.SetKeyboardFocus(null);
+                    gui.inputSystem.SetKeyboardFocus(null);
                     break;
                 case SDL.SDL_Scancode.SDL_SCANCODE_LEFT:
                     if (shift) {

Yafc.UI/ImGui/ImGuiUtils.cs

@@ -35,7 +35,7 @@ public static class ImGuiUtils {
 
         public static ButtonEvent BuildButton(this ImGui gui, Rect rect, SchemeColor normal, SchemeColor over, SchemeColor down = SchemeColor.None, uint button = SDL.SDL_BUTTON_LEFT) {
             if (button == 0) {
-                button = (uint)InputSystem.Instance.mouseDownButton;
+                button = (uint)gui.inputSystem.mouseDownButton;
             }
 
             switch (gui.action) {