Add MrGameEng.UI module integrating Myra

scene.UseUI() creates a per-scene Myra Desktop and registers
UiRenderSystem last in the draw phase (UI on top, window pixels).
GameHost now exposes itself as a Game service (Myra needs the instance;
useful for games too). Myra was picked over Gum/ImGui for the
FontStashSharp ecosystem fit, pipeline-free assets and maturity; its
internal SpriteBatch use is a documented exception to the engine rule.

Sample: on-screen HUD replaces window-title-only stats — live FPS label,
music volume slider and scene-switch buttons on both scenes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

samples/MrGameEng.Sample/MrGameEng.Sample.csproj

@@ -11,6 +11,7 @@
     <ProjectReference Include="..\..\src\MrGameEng.Input\MrGameEng.Input.csproj" />
     <ProjectReference Include="..\..\src\MrGameEng.Audio\MrGameEng.Audio.csproj" />
     <ProjectReference Include="..\..\src\MrGameEng.Assets\MrGameEng.Assets.csproj" />
+    <ProjectReference Include="..\..\src\MrGameEng.UI\MrGameEng.UI.csproj" />
     <ProjectReference Include="..\..\src\MrGameEng.Assets.Generator\MrGameEng.Assets.Generator.csproj"
                       OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
   </ItemGroup>

samples/MrGameEng.Sample/SampleSystems.cs

@@ -113,8 +113,9 @@ public sealed class SceneHotkeysSystem(
     }
 }
 
-/// <summary>FPS и статистика рендера в заголовке окна (обновляется 4 раза в секунду).</summary>
-public sealed class TitleStatsSystem(EngineContext context, Renderer2D renderer, string sceneName) : BaseSystem
+/// <summary>FPS и статистика рендера: в HUD-лейбл и в заголовок окна (4 раза в секунду).</summary>
+public sealed class StatsSystem(
+    EngineContext context, Renderer2D renderer, string sceneName, Myra.Graphics2D.UI.Label? hudLabel = null) : BaseSystem
 {
     private float _accumulated;
     private int _frames;
@@ -131,8 +132,13 @@ public sealed class TitleStatsSystem(EngineContext context, Renderer2D renderer,
         var fps = _frames / _accumulated;
         _accumulated = 0f;
         _frames = 0;
-        context.Services.Get<GameWindow>().Title =
-            $"MrGameEng Sample — {sceneName} | {fps:F0} FPS | sprites: {renderer.SubmittedSprites} | culled: {renderer.CulledSprites} | draw calls: {renderer.DrawCalls}";
+        var stats =
+            $"{fps:F0} FPS | sprites: {renderer.SubmittedSprites} | culled: {renderer.CulledSprites} | draw calls: {renderer.DrawCalls}";
+        context.Services.Get<GameWindow>().Title = $"MrGameEng Sample — {sceneName} | {stats}";
+        if (hudLabel is not null)
+        {
+            hudLabel.Text = $"{sceneName}\n{stats}";
+        }
     }
 }
 

samples/MrGameEng.Sample/Scenes/MainScene.cs

@@ -5,6 +5,8 @@ using MrGameEng.Audio;
 using MrGameEng.Core;
 using MrGameEng.Graphics;
 using MrGameEng.Input;
+using MrGameEng.UI;
+using Myra.Graphics2D.UI;
 
 namespace MrGameEng.Sample.Scenes;
 
@@ -90,11 +92,32 @@ public sealed class MainScene : Scene
         var hud = new Sprite(shapeRegions[3], SampleLayers.Ui);
         Store.CreateEntity(new Transform2D(new Vector2(16f, 16f)), hud);
 
+        // UI (Myra): HUD со статистикой, слайдер громкости, кнопка перехода. После UseRenderer2D!
+        var desktop = this.UseUI();
+        var statsLabel = new Label();
+        var volumeSlider = new HorizontalSlider { Minimum = 0f, Maximum = 1f, Value = audio.Music.Volume, Width = 180 };
+        volumeSlider.ValueChanged += (_, _) => audio.Music.Volume = volumeSlider.Value;
+        var switchButton = new Button { Content = new Label { Text = "Stress scene (Tab)" } };
+        switchButton.Click += (_, _) =>
+        {
+            if (!Context.Scenes.IsTransitioning)
+            {
+                Context.Scenes.Switch(new StressScene(), Transition.Fade(0.8f));
+            }
+        };
+
+        var panel = new VerticalStackPanel { Left = 12, Top = 12, Spacing = 6 };
+        panel.Widgets.Add(statsLabel);
+        panel.Widgets.Add(new Label { Text = "Music volume (M — pause)" });
+        panel.Widgets.Add(volumeSlider);
+        panel.Widgets.Add(switchButton);
+        desktop.Root = panel;
+
         UpdateSystems.Add(new PlayerControlSystem(player, actions, audio, beep));
         UpdateSystems.Add(new BounceSystem(WorldBounds));
         UpdateSystems.Add(new CameraControlSystem(camera, player, input));
         UpdateSystems.Add(new SceneHotkeysSystem(Context, actions, () => new StressScene(), Transition.Fade(0.8f)));
-        UpdateSystems.Add(new TitleStatsSystem(Context, renderer, "Main"));
+        UpdateSystems.Add(new StatsSystem(Context, renderer, "Main", statsLabel));
 
         var music = audio.Music;
         if (!music.IsPlaying)

samples/MrGameEng.Sample/Scenes/StressScene.cs

@@ -4,6 +4,7 @@ using MrGameEng.Assets;
 using MrGameEng.Core;
 using MrGameEng.Graphics;
 using MrGameEng.Input;
+using MrGameEng.UI;
 
 namespace MrGameEng.Sample.Scenes;
 
@@ -52,10 +53,28 @@ public sealed class StressScene : Scene
 
         var camera = Store.CreateEntity(new Camera(Vector2.Zero, zoom: 0.3f));
 
+        var desktop = this.UseUI();
+        var statsLabel = new Myra.Graphics2D.UI.Label();
+        var backButton = new Myra.Graphics2D.UI.Button
+        {
+            Content = new Myra.Graphics2D.UI.Label { Text = "Back to main (Tab)" },
+        };
+        backButton.Click += (_, _) =>
+        {
+            if (!Context.Scenes.IsTransitioning)
+            {
+                Context.Scenes.Switch(new MainScene(), Transition.Wipe(0.8f, Color.DarkSlateBlue));
+            }
+        };
+        var panel = new Myra.Graphics2D.UI.VerticalStackPanel { Left = 12, Top = 12, Spacing = 6 };
+        panel.Widgets.Add(statsLabel);
+        panel.Widgets.Add(backButton);
+        desktop.Root = panel;
+
         UpdateSystems.Add(new BounceSystem(WorldBounds));
         UpdateSystems.Add(new StressCameraSystem(camera, input));
         UpdateSystems.Add(new SceneHotkeysSystem(Context, actions, () => new MainScene(), Transition.Wipe(0.8f, Color.DarkSlateBlue)));
-        UpdateSystems.Add(new TitleStatsSystem(Context, renderer, $"Stress {SpriteCount:N0}"));
+        UpdateSystems.Add(new StatsSystem(Context, renderer, $"Stress {SpriteCount:N0}", statsLabel));
     }
 
     /// <summary>Только зум колесом — чтобы регулировать число видимых спрайтов.</summary>