Added composition support to the headless platform

samples/ControlCatalog.NetCore/Program.cs

@@ -53,7 +53,11 @@ namespace ControlCatalog.NetCore
             else if (args.Contains("--full-headless"))
             {
                 return builder
-                    .UseHeadless(true)
+                    .UseHeadless(new AvaloniaHeadlessPlatformOptions
+                    {
+                        UseHeadlessDrawing = true,
+                        UseComposition = false
+                    })
                     .AfterSetup(_ =>
                     {
                         DispatcherTimer.RunOnce(async () =>
@@ -63,12 +67,11 @@ namespace ControlCatalog.NetCore
                             var tc = window.GetLogicalDescendants().OfType<TabControl>().First();
                             foreach (var page in tc.Items.Cast<TabItem>().ToList())
                             {
-                                // Skip DatePicker because of some layout bug in grid
-                                if (page.Header.ToString() == "DatePicker")
+                                if (page.Header.ToString() == "DatePicker" || page.Header.ToString() == "TreeView")
                                     continue;
                                 Console.WriteLine("Selecting " + page.Header);
                                 tc.SelectedItem = page;
-                                await Task.Delay(500);
+                                await Task.Delay(50);
                             }
                             Console.WriteLine("Selecting the first page");
                             tc.SelectedItem = tc.Items.OfType<object>().First();
@@ -77,7 +80,7 @@ namespace ControlCatalog.NetCore
                             for (var c = 0; c < 3; c++)
                             {
                                 GC.Collect(2, GCCollectionMode.Forced);
-                                await Task.Delay(500);
+                                await Task.Delay(00);
                             }
 
                             void FormatMem(string metric, long bytes)
@@ -87,7 +90,6 @@ namespace ControlCatalog.NetCore
 
                             FormatMem("GC allocated bytes", GC.GetTotalMemory(true));
                             FormatMem("WorkingSet64", Process.GetCurrentProcess().WorkingSet64);
-
                         }, TimeSpan.FromSeconds(1));
                     })
                     .StartWithClassicDesktopLifetime(args);

src/Avalonia.Headless.Vnc/HeadlessVncPlatformExtensions.cs

@@ -20,7 +20,11 @@ namespace Avalonia
             var tcpServer = new TcpListener(host == null ? IPAddress.Loopback : IPAddress.Parse(host), port);
             tcpServer.Start();    
             return builder
-                .UseHeadless(false)
+                .UseHeadless(new AvaloniaHeadlessPlatformOptions
+                {
+                    UseComposition = true,
+                    UseHeadlessDrawing = false
+                })
                 .AfterSetup(_ =>
                 {
                     var lt = ((IClassicDesktopStyleApplicationLifetime)builder.Instance.ApplicationLifetime);

src/Avalonia.Headless/AvaloniaHeadlessPlatform.cs

@@ -7,12 +7,14 @@ using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Platform;
 using Avalonia.Rendering;
+using Avalonia.Rendering.Composition;
 using Avalonia.Threading;
 
 namespace Avalonia.Headless
 {
     public static class AvaloniaHeadlessPlatform
     {
+        internal static Compositor Compositor { get; private set; }
         class RenderTimer : DefaultRenderTimer
         {
             private readonly int _framesPerSecond;
@@ -55,7 +57,7 @@ namespace Avalonia.Headless
             public ITrayIconImpl CreateTrayIcon() => null;
         }
         
-        internal static void Initialize()
+        internal static void Initialize(AvaloniaHeadlessPlatformOptions opts)
         {
             AvaloniaLocator.CurrentMutable
                 .Bind<IPlatformThreadingInterface>().ToConstant(new HeadlessPlatformThreadingInterface())
@@ -71,6 +73,8 @@ namespace Avalonia.Headless
                 .Bind<ITextShaperImpl>().ToSingleton<HeadlessTextShaperStub>()
                 .Bind<IWindowingPlatform>().ToConstant(new HeadlessWindowingPlatform())
                 .Bind<PlatformHotkeyConfiguration>().ToSingleton<PlatformHotkeyConfiguration>();
+            if (opts.UseComposition)
+                Compositor = new Compositor(AvaloniaLocator.Current.GetRequiredService<IRenderLoop>(), null);
         }
 
 
@@ -82,15 +86,21 @@ namespace Avalonia.Headless
 
         }
     }
-    
+
+    public class AvaloniaHeadlessPlatformOptions
+    {
+        public bool UseComposition { get; set; } = true;
+        public bool UseHeadlessDrawing { get; set; } = true;
+    }
+
     public static class AvaloniaHeadlessPlatformExtensions
     {
-        public static T UseHeadless<T>(this T builder, bool headlessDrawing = true) 
+        public static T UseHeadless<T>(this T builder, AvaloniaHeadlessPlatformOptions opts) 
             where T : AppBuilderBase<T>, new()
         {
-            if (headlessDrawing)
+            if(opts.UseHeadlessDrawing)
                 builder.UseRenderingSubsystem(HeadlessPlatformRenderInterface.Initialize, "Headless");
-            return builder.UseWindowingSubsystem(AvaloniaHeadlessPlatform.Initialize, "Headless");
+            return builder.UseWindowingSubsystem(() => AvaloniaHeadlessPlatform.Initialize(opts), "Headless");
         }
     }
 }

src/Avalonia.Headless/HeadlessPlatformRenderInterface.cs

@@ -418,7 +418,6 @@ namespace Avalonia.Headless
 
             public void DrawLine(IPen pen, Point p1, Point p2)
             {
-                throw new NotImplementedException();
             }
 
             public void DrawGeometry(IBrush brush, IPen pen, IGeometryImpl geometry)

src/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -10,6 +10,7 @@ using Avalonia.Input.Raw;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 using Avalonia.Rendering;
+using Avalonia.Rendering.Composition;
 using Avalonia.Threading;
 using Avalonia.Utilities;
 
@@ -52,7 +53,9 @@ namespace Avalonia.Headless
         public Action<double> ScalingChanged { get; set; }
 
         public IRenderer CreateRenderer(IRenderRoot root)
-            => new DeferredRenderer(root, AvaloniaLocator.Current.GetService<IRenderLoop>());
+            => AvaloniaHeadlessPlatform.Compositor != null
+                ? new CompositingRenderer(root, AvaloniaHeadlessPlatform.Compositor)
+                : new DeferredRenderer(root, AvaloniaLocator.Current.GetRequiredService<IRenderLoop>());
 
         public void Invalidate(Rect rect)
         {