Minor changes, missing documentation

src/Headless/Avalonia.Headless.Vnc/HeadlessVncFramebufferSource.cs

@@ -2,6 +2,7 @@
 using System.Runtime.InteropServices;
 using Avalonia.Controls;
 using Avalonia.Input;
+using Avalonia.Platform;
 using Avalonia.Threading;
 using RemoteViewing.Vnc;
 using RemoteViewing.Vnc.Server;
@@ -68,7 +69,7 @@ namespace Avalonia.Headless.Vnc
         {
             lock (_lock)
             {
-                using (var bmpRef = Window.GetLastRenderedFrame())
+                using (var bmpRef = Window.CaptureRenderedFrame())
                 {
                     if (bmpRef == null)
                         return _framebuffer;

src/Headless/Avalonia.Headless.XUnit/AvaloniaTestFrameworkAttribute.cs

@@ -5,7 +5,7 @@ using Xunit.Sdk;
 namespace Avalonia.Headless.XUnit;
 
 /// <summary>
-/// 
+/// Sets up global avalonia test framework using avalonia application builder passed as a parameter.
 /// </summary>
 [TestFrameworkDiscoverer("Avalonia.Headless.XUnit.AvaloniaTestFrameworkTypeDiscoverer", "Avalonia.Headless.XUnit")]
 [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = false)]

src/Headless/Avalonia.Headless/Avalonia.Headless.csproj

@@ -11,4 +11,8 @@
   <Import Project="..\..\..\build\DevAnalyzers.props" />
   <Import Project="..\..\..\build\TrimmingEnable.props" />
   <Import Project="..\..\..\build\NullableEnable.props" />
+
+  <ItemGroup Label="InternalsVisibleTo">
+    <InternalsVisibleTo Include="Avalonia.Headless.Vnc, PublicKey=$(AvaloniaPublicKey)" />
+  </ItemGroup>
 </Project>

src/Headless/Avalonia.Headless/AvaloniaHeadlessPlatform.cs

@@ -72,7 +72,11 @@ namespace Avalonia.Headless
             Compositor = new Compositor(AvaloniaLocator.Current.GetRequiredService<IRenderLoop>(), null);
         }
 
-
+        /// <summary>
+        /// Forces renderer to process a rendering timer tick.
+        /// Use this method before calling <see cref="HeadlessWindowExtensions.GetLastRenderedFrame"/>. 
+        /// </summary>
+        /// <param name="count">Count of frames to be ticked on the timer.</param>
         public static void ForceRenderTimerTick(int count = 1)
         {
             var timer = AvaloniaLocator.Current.GetService<IRenderTimer>() as RenderTimer;

src/Headless/Avalonia.Headless/HeadlessWindowExtensions.cs

@@ -3,40 +3,78 @@ using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Media.Imaging;
+using Avalonia.Platform;
 using Avalonia.Threading;
 
 namespace Avalonia.Headless;
 
 public static class HeadlessWindowExtensions
 {
+    /// <summary>
+    /// Triggers a renderer timer tick and captures last rendered frame.
+    /// </summary>
+    /// <returns>Bitmap with last rendered frame. Null, if nothing was rendered.</returns>
     public static Bitmap? CaptureRenderedFrame(this TopLevel topLevel)
     {
-        var impl = GetImpl(topLevel);
+        Dispatcher.UIThread.RunJobs();
         AvaloniaHeadlessPlatform.ForceRenderTimerTick();
-        return impl.GetLastRenderedFrame();
+        return topLevel.GetLastRenderedFrame();
     }
     
-    public static Bitmap? GetLastRenderedFrame(this TopLevel topLevel) =>
-        GetImpl(topLevel).GetLastRenderedFrame();
+    /// <summary>
+    /// Reads last rendered frame.
+    /// Note, in order to trigger rendering timer, call <see cref="AvaloniaHeadlessPlatform.ForceRenderTimerTick"/> method.  
+    /// </summary>
+    /// <returns>Bitmap with last rendered frame. Null, if nothing was rendered.</returns>
+    public static Bitmap? GetLastRenderedFrame(this TopLevel topLevel)
+    {
+        if (AvaloniaLocator.Current.GetService<IPlatformRenderInterface>() is HeadlessPlatformRenderInterface)
+        {
+            throw new NotSupportedException("To capture a rendered frame, make sure that headless application was initialized with '.UseSkia()' and disabled 'UseHeadlessDrawing' in the 'AvaloniaHeadlessPlatformOptions'.");
+        }
+
+        return GetImpl(topLevel).GetLastRenderedFrame();
+    }
 
+    /// <summary>
+    /// Simulates keyboard press on the headless window/toplevel.
+    /// </summary>
     public static void KeyPress(this TopLevel topLevel, Key key, RawInputModifiers modifiers) =>
         GetImpl(topLevel).KeyPress(key, modifiers);
 
+    /// <summary>
+    /// Simulates keyboard release on the headless window/toplevel.
+    /// </summary>
     public static void KeyRelease(this TopLevel topLevel, Key key, RawInputModifiers modifiers) =>
         GetImpl(topLevel).KeyRelease(key, modifiers);
 
+    /// <summary>
+    /// Simulates mouse down on the headless window/toplevel.
+    /// </summary>
     public static void MouseDown(this TopLevel topLevel, Point point, MouseButton button,
         RawInputModifiers modifiers = RawInputModifiers.None) => GetImpl(topLevel).MouseDown(point, button, modifiers);
 
+    /// <summary>
+    /// Simulates mouse move on the headless window/toplevel.
+    /// </summary>
     public static void MouseMove(this TopLevel topLevel, Point point,
         RawInputModifiers modifiers = RawInputModifiers.None) => GetImpl(topLevel).MouseMove(point, modifiers);
 
+    /// <summary>
+    /// Simulates mouse up on the headless window/toplevel.
+    /// </summary>
     public static void MouseUp(this TopLevel topLevel, Point point, MouseButton button,
         RawInputModifiers modifiers = RawInputModifiers.None) => GetImpl(topLevel).MouseUp(point, button, modifiers);
 
+    /// <summary>
+    /// Simulates mouse wheel on the headless window/toplevel.
+    /// </summary>
     public static void MouseWheel(this TopLevel topLevel, Point point, Vector delta,
         RawInputModifiers modifiers = RawInputModifiers.None) => GetImpl(topLevel).MouseWheel(point, delta, modifiers);
 
+    /// <summary>
+    /// Simulates drag'n'drop target on the headless window/toplevel.
+    /// </summary>
     public static void DragDrop(this TopLevel topLevel, Point point, RawDragEventType type, IDataObject data,
         DragDropEffects effects, RawInputModifiers modifiers = RawInputModifiers.None) =>
         GetImpl(topLevel).DragDrop(point, type, data, effects, modifiers);

tests/Avalonia.Headless.UnitTests/RenderingTests.cs

@@ -27,8 +27,6 @@ public class RenderingTests
         };
         window.Show();
 
-        Dispatcher.UIThread.RunJobs();
-        AvaloniaHeadlessPlatform.ForceRenderTimerTick();
         var frame = window.CaptureRenderedFrame();
         Assert.NotNull(frame);
     }