feat: Draw a main-viewport-big notifier on screen whenever in gamepad mode

This notifier is a light grey-ish background and some text in the upper
left corner of the main viewport.

Dalamud/Interface/DalamudInterface.cs

@@ -35,6 +35,7 @@ namespace Dalamud.Interface
         private readonly ComponentDemoWindow componentDemoWindow;
         private readonly ColorDemoWindow colorDemoWindow;
         private readonly ScratchpadWindow scratchpadWindow;
+        private readonly GamepadModeNotifierWindow gamepadModeNotifierWindow;
 
         private readonly WindowSystem windowSystem = new WindowSystem("DalamudCore");
 
@@ -116,6 +117,9 @@ namespace Dalamud.Interface
             };
             this.windowSystem.AddWindow(this.scratchpadWindow);
 
+            this.gamepadModeNotifierWindow = new GamepadModeNotifierWindow();
+            this.windowSystem.AddWindow(this.gamepadModeNotifierWindow);
+
             Log.Information("[DUI] Windows added");
 
             if (dalamud.Configuration.LogOpenAtStartup)
@@ -553,5 +557,13 @@ namespace Dalamud.Interface
         {
             this.scratchpadWindow.IsOpen ^= true;
         }
+
+        /// <summary>
+        /// Toggle the gamepad notifier window window.
+        /// </summary>
+        internal void ToggleGamePadNotifierWindow()
+        {
+            this.gamepadModeNotifierWindow.IsOpen ^= true;
+        }
     }
 }

Dalamud/Interface/GamepadModeNotifierWindow.cs

@@ -0,0 +1,41 @@
+using System.Numerics;
+
+using Dalamud.Interface.Windowing;
+using ImGuiNET;
+
+namespace Dalamud.Interface
+{
+    /// <summary>
+    /// Class responsible for drawing a notifier on screen that gamepad mode is active.
+    /// </summary>
+    internal class GamepadModeNotifierWindow : Window
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GamepadModeNotifierWindow"/> class.
+        /// </summary>
+        public GamepadModeNotifierWindow()
+            : base(
+                "###DalamudGamepadModeNotifier",
+                ImGuiWindowFlags.NoDecoration | ImGuiWindowFlags.NoMove | ImGuiWindowFlags.NoMouseInputs
+                | ImGuiWindowFlags.NoFocusOnAppearing | ImGuiWindowFlags.NoBackground | ImGuiWindowFlags.NoNav
+                | ImGuiWindowFlags.NoInputs | ImGuiWindowFlags.NoCollapse | ImGuiWindowFlags.NoSavedSettings,
+                true)
+        {
+            this.Size = Vector2.Zero;
+            this.SizeCondition = ImGuiCond.Always;
+            this.IsOpen = false;
+        }
+
+        /// <summary>
+        /// Draws a light grey-ish, main-viewport-big filled rect in the background draw list alongside a text indicating gamepad mode.
+        /// </summary>
+        public override void Draw()
+        {
+            var drawList = ImGui.GetBackgroundDrawList();
+            drawList.PushClipRectFullScreen();
+            drawList.AddRectFilled(Vector2.Zero, ImGuiHelpers.MainViewport.Size, 0x661A1A1A);
+            drawList.AddText(Vector2.One, 0xFFFFFFFF, "Gamepad mode is ON. Press R1+L3 to deactivate, press R3 to toggle PluginInstaller.");
+            drawList.PopClipRect();
+        }
+    }
+}

Dalamud/Interface/InterfaceManager.cs

@@ -488,6 +488,7 @@ namespace Dalamud.Interface
             {
                 ImGui.GetIO().ConfigFlags ^= ImGuiConfigFlags.NavEnableGamepad;
                 this.dalamud.ClientState.GamepadState.NavEnableGamepad ^= true;
+                this.dalamud.DalamudUi.ToggleGamePadNotifierWindow();
             }
 
             if (gamepadEnabled