Create DiagnosticTextRenderer on the UI thread

src/Avalonia.Base/Rendering/Composition/Compositor.Factories.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using Avalonia.Platform;
 using Avalonia.Rendering.Composition.Animations;
 using Avalonia.Rendering.Composition.Server;
 
@@ -15,7 +14,7 @@ public partial class Compositor
     /// <returns></returns>
     public CompositionTarget CreateCompositionTarget(Func<IEnumerable<object>> surfaces)
     {
-        return new CompositionTarget(this, new ServerCompositionTarget(_server, surfaces));
+        return new CompositionTarget(this, new ServerCompositionTarget(_server, surfaces, DiagnosticTextRenderer));
     }
     
     public CompositionContainerVisual CreateContainerVisual() => new(this, new ServerCompositionContainerVisual(_server));

src/Avalonia.Base/Rendering/Composition/Compositor.cs

@@ -35,11 +35,14 @@ namespace Avalonia.Rendering.Composition
         private Task? _pendingBatch;
         private readonly object _pendingBatchLock = new();
         private List<Action> _pendingServerCompositorJobs = new();
+        private DiagnosticTextRenderer? _diagnosticTextRenderer;
 
         internal IEasing DefaultEasing { get; }
 
+        private DiagnosticTextRenderer DiagnosticTextRenderer
+            => _diagnosticTextRenderer ??= new(Typeface.Default.GlyphTypeface, 12.0);
+
         internal event Action? AfterCommit;
-        
 
         /// <summary>
         /// Creates a new compositor on a specified render loop that would use a particular GPU

src/Avalonia.Base/Rendering/Composition/Server/DiagnosticTextRenderer.cs

@@ -14,7 +14,21 @@ namespace Avalonia.Rendering.Composition.Server
 
         private readonly GlyphRun[] _runs = new GlyphRun[LastChar - FirstChar + 1];
 
-        public double MaxHeight { get; }
+        public double GetMaxHeight()
+        {
+            var maxHeight = 0.0;
+
+            for (var c = FirstChar; c <= LastChar; c++)
+            {
+                var height = _runs[c - FirstChar].Size.Height;
+                if (height > maxHeight)
+                {
+                    maxHeight = height;
+                }
+            }
+
+            return maxHeight;
+        }
 
         public DiagnosticTextRenderer(IGlyphTypeface typeface, double fontRenderingEmSize)
         {
@@ -24,9 +38,7 @@ namespace Avalonia.Rendering.Composition.Server
                 var index = c - FirstChar;
                 chars[index] = c;
                 var glyph = typeface.GetGlyph(c);
-                var run = new GlyphRun(typeface, fontRenderingEmSize, chars.AsMemory(index, 1), new[] { glyph });
-                _runs[index] = run;
-                MaxHeight = Math.Max(run.Size.Height, MaxHeight);
+                _runs[index] = new GlyphRun(typeface, fontRenderingEmSize, chars.AsMemory(index, 1), new[] { glyph });
             }
         }
 

src/Avalonia.Base/Rendering/Composition/Server/FrameTimeGraph.cs

@@ -44,7 +44,7 @@ internal sealed class FrameTimeGraph
         _graphPen = new ImmutablePen(Brushes.Blue);
         _frameValues = new double[maxFrames];
         _size = size;
-        _headerSize = new Size(size.Width, textRenderer.MaxHeight + HeaderPadding * 2.0);
+        _headerSize = new Size(size.Width, textRenderer.GetMaxHeight() + HeaderPadding * 2.0);
         _graphSize = new Size(size.Width, size.Height - _headerSize.Height);
         _defaultMaxY = defaultMaxY;
         _title = title;

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionTarget.cs

@@ -21,9 +21,9 @@ namespace Avalonia.Rendering.Composition.Server
     {
         private readonly ServerCompositor _compositor;
         private readonly Func<IEnumerable<object>> _surfaces;
+        private readonly DiagnosticTextRenderer _diagnosticTextRenderer;
         private static long s_nextId = 1;
         private IRenderTarget? _renderTarget;
-        private DiagnosticTextRenderer? _diagnosticTextRenderer;
         private FpsCounter? _fpsCounter;
         private FrameTimeGraph? _renderTimeGraph;
         private FrameTimeGraph? _layoutTimeGraph;
@@ -42,11 +42,8 @@ namespace Avalonia.Rendering.Composition.Server
         public ReadbackIndices Readback { get; } = new();
         public int RenderedVisuals { get; set; }
 
-        private DiagnosticTextRenderer DiagnosticTextRenderer
-            => _diagnosticTextRenderer ??= new DiagnosticTextRenderer(Typeface.Default.GlyphTypeface, 12.0);
-
         private FpsCounter FpsCounter
-            => _fpsCounter ??= new FpsCounter(DiagnosticTextRenderer);
+            => _fpsCounter ??= new FpsCounter(_diagnosticTextRenderer);
 
         private FrameTimeGraph LayoutTimeGraph
             => _layoutTimeGraph ??= CreateTimeGraph("Layout");
@@ -54,16 +51,18 @@ namespace Avalonia.Rendering.Composition.Server
         private FrameTimeGraph RenderTimeGraph
             => _renderTimeGraph ??= CreateTimeGraph("Render");
 
-        public ServerCompositionTarget(ServerCompositor compositor, Func<IEnumerable<object>> surfaces) :
-            base(compositor)
+        public ServerCompositionTarget(ServerCompositor compositor, Func<IEnumerable<object>> surfaces,
+            DiagnosticTextRenderer diagnosticTextRenderer)
+            : base(compositor)
         {
             _compositor = compositor;
             _surfaces = surfaces;
+            _diagnosticTextRenderer = diagnosticTextRenderer;
             Id = Interlocked.Increment(ref s_nextId);
         }
 
         private FrameTimeGraph CreateTimeGraph(string title)
-            => new(360, new Size(360.0, 64.0), 1000.0 / 60.0, title, DiagnosticTextRenderer);
+            => new(360, new Size(360.0, 64.0), 1000.0 / 60.0, title, _diagnosticTextRenderer);
 
         partial void OnIsEnabledChanged()
         {