add a render info message so dpi can be set.

src/Avalonia.Controls/Remote/Server/RemoteServerTopLevelImpl.cs

@@ -45,6 +45,13 @@ namespace Avalonia.Controls.Remote.Server
                     }
                     Dispatcher.UIThread.Post(RenderIfNeeded);
                 }
+                if(obj is ClientRenderInfoMessage renderInfo)
+                {
+                    lock(_lock)
+                    {
+                        _dpi = new Vector(renderInfo.DpiX, renderInfo.DpiY);
+                    }
+                }
                 if (obj is ClientSupportedPixelFormatsMessage supportedFormats)
                 {
                     lock (_lock)
@@ -74,7 +81,6 @@ namespace Avalonia.Controls.Remote.Server
                                     allocation = _pendingAllocation;
                                     _pendingAllocation = null;
                                 }
-                                _dpi = new Vector(allocation.DpiX, allocation.DpiY);
                                 ClientSize = new Size(allocation.Width, allocation.Height);
                                 RenderIfNeeded();
                             });

src/Avalonia.DesignerSupport/DesignWindowLoader.cs

@@ -13,7 +13,7 @@ namespace Avalonia.DesignerSupport
 {
     public class DesignWindowLoader
     {
-        public static Window LoadDesignerWindow(string xaml, string assemblyPath, Vector dpi)
+        public static Window LoadDesignerWindow(string xaml, string assemblyPath)
         {
             Window window;
             Control control;
@@ -70,8 +70,6 @@ namespace Avalonia.DesignerSupport
                 if (!window.IsSet(Window.SizeToContentProperty))
                     window.SizeToContent = SizeToContent.WidthAndHeight;
             }
-            
-            (window.PlatformImpl as RemoteServerTopLevelImpl).SetDpi(dpi);
 
             window.Show();
             Design.ApplyDesignModeProperties(window, control);

src/Avalonia.DesignerSupport/Remote/RemoteDesignerEntryPoint.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Net;
 using System.Reflection;
@@ -15,6 +15,8 @@ namespace Avalonia.DesignerSupport.Remote
     {
         private static ClientSupportedPixelFormatsMessage s_supportedPixelFormats;
         private static ClientViewportAllocatedMessage s_viewportAllocatedMessage;
+        private static ClientRenderInfoMessage s_renderInfoMessage;
+
         private static IAvaloniaRemoteTransportConnection s_transport;
         class CommandLineArgs
         {
@@ -161,7 +163,8 @@ namespace Avalonia.DesignerSupport.Remote
             PreviewerWindowingPlatform.PreFlightMessages = new List<object>
             {
                 s_supportedPixelFormats,
-                s_viewportAllocatedMessage
+                s_viewportAllocatedMessage,
+                s_renderInfoMessage
             };
         }
 
@@ -173,6 +176,11 @@ namespace Avalonia.DesignerSupport.Remote
                 s_supportedPixelFormats = formats;
                 RebuildPreFlight();
             }
+            if (obj is ClientRenderInfoMessage renderInfo)
+            {
+                s_renderInfoMessage = renderInfo;
+                RebuildPreFlight();
+            }
             if (obj is ClientViewportAllocatedMessage viewport)
             {
                 s_viewportAllocatedMessage = viewport;
@@ -191,8 +199,7 @@ namespace Avalonia.DesignerSupport.Remote
                 s_currentWindow = null;
                 try
                 {
-                    var dpi = s_viewportAllocatedMessage != null ? new Vector(s_viewportAllocatedMessage.DpiX, s_viewportAllocatedMessage.DpiY) : new Vector(96, 96);
-                    s_currentWindow = DesignWindowLoader.LoadDesignerWindow(xaml.Xaml, xaml.AssemblyPath, dpi);
+                    s_currentWindow = DesignWindowLoader.LoadDesignerWindow(xaml.Xaml, xaml.AssemblyPath);
                     s_transport.Send(new UpdateXamlResultMessage(){Handle = s_currentWindow.PlatformImpl?.Handle?.Handle.ToString()});
                 }
                 catch (Exception e)

src/Avalonia.Remote.Protocol/ViewportMessages.cs

@@ -37,6 +37,13 @@
         public PixelFormat[] Formats { get; set; }
     }
 
+    [AvaloniaRemoteMessageGuid("7A3c25d3-3652-438D-8EF1-86E942CC96C0")]
+    public class ClientRenderInfoMessage
+    {
+        public double DpiX { get; set; }
+        public double DpiY { get; set; }
+    }
+
     [AvaloniaRemoteMessageGuid("68014F8A-289D-4851-8D34-5367EDA7F827")]
     public class FrameReceivedMessage
     {