Document and test macOS Metal support

Smoke/AvaloniaStaticLinkSmoke/App.axaml.cs

@@ -1,6 +1,7 @@
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
+using Avalonia.Threading;
 
 namespace AvaloniaStaticLinkSmoke;
 
@@ -15,7 +16,28 @@ public sealed partial class App : Application
     {
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
-            desktop.MainWindow = new MainWindow();
+            var renderer = Environment.GetEnvironmentVariable("STATICLINK_MAC_RENDERER") ?? "opengl";
+            var autoClose = Environment.GetEnvironmentVariable("STATICLINK_SMOKE_AUTOCLOSE") == "1";
+            desktop.MainWindow = new MainWindow(autoClose ? CompleteSmoke : null);
+
+            void CompleteSmoke(string backend)
+            {
+                Dispatcher.UIThread.Post(() =>
+                {
+                    if (!renderer.Equals("metal", StringComparison.OrdinalIgnoreCase) ||
+                        backend.Equals("Metal", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Console.WriteLine($"STATICLINK_SMOKE_READY={renderer}");
+                    }
+                    else
+                    {
+                        Console.Error.WriteLine($"Expected the Metal renderer, but the active Skia backend was {backend}.");
+                        Environment.ExitCode = 1;
+                    }
+
+                    desktop.MainWindow?.Close();
+                });
+            }
         }
 
         base.OnFrameworkInitializationCompleted();

Smoke/AvaloniaStaticLinkSmoke/MainWindow.axaml.cs

@@ -1,11 +1,60 @@
+using Avalonia;
 using Avalonia.Controls;
+using Avalonia.Media;
+using Avalonia.Rendering.SceneGraph;
+using Avalonia.Skia;
 
 namespace AvaloniaStaticLinkSmoke;
 
 public sealed partial class MainWindow : Window
 {
-    public MainWindow()
+    private readonly Action<string>? _renderResult;
+    private int _renderResultReported;
+
+    public MainWindow() : this(null)
     {
+    }
+
+    public MainWindow(Action<string>? renderResult)
+    {
+        _renderResult = renderResult;
         InitializeComponent();
     }
+
+    public override void Render(DrawingContext context)
+    {
+        base.Render(context);
+        if (_renderResult is not null)
+        {
+            context.Custom(new MetalBackendProbe(new Rect(Bounds.Size), ReportMetalResult));
+        }
+    }
+
+    private void ReportMetalResult(string backend)
+    {
+        if (Interlocked.Exchange(ref _renderResultReported, 1) == 0)
+        {
+            _renderResult?.Invoke(backend);
+        }
+    }
+
+    private sealed class MetalBackendProbe(Rect bounds, Action<string> report) : ICustomDrawOperation
+    {
+        public Rect Bounds { get; } = bounds;
+
+        public void Dispose()
+        {
+        }
+
+        public bool Equals(ICustomDrawOperation? other) => false;
+
+        public bool HitTest(Point point) => false;
+
+        public void Render(ImmediateDrawingContext context)
+        {
+            var feature = context.TryGetFeature(typeof(ISkiaSharpApiLeaseFeature)) as ISkiaSharpApiLeaseFeature;
+            using var lease = feature?.Lease();
+            report(lease?.GrContext?.Backend.ToString() ?? "Software");
+        }
+    }
 }

Smoke/AvaloniaStaticLinkSmoke/Program.cs

@@ -39,14 +39,16 @@ internal static class Program
 
         if (OperatingSystem.IsMacOS())
         {
-            builder = builder.With(new AvaloniaNativePlatformOptions
+            var renderer = Environment.GetEnvironmentVariable("STATICLINK_MAC_RENDERER");
+            if (!string.Equals(renderer, "default", StringComparison.OrdinalIgnoreCase))
             {
-                RenderingMode =
-                [
-                    AvaloniaNativeRenderingMode.OpenGl,
-                    AvaloniaNativeRenderingMode.Software
-                ]
-            });
+                builder = builder.With(new AvaloniaNativePlatformOptions
+                {
+                    RenderingMode = string.Equals(renderer, "metal", StringComparison.OrdinalIgnoreCase)
+                        ? [AvaloniaNativeRenderingMode.Metal]
+                        : [AvaloniaNativeRenderingMode.OpenGl, AvaloniaNativeRenderingMode.Software]
+                });
+            }
         }
 
         return builder;