[X11] Set WM_CLASS property (default to entry assembly name)

#2369

src/Avalonia.X11/X11Platform.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
 using Avalonia.Input;
@@ -24,6 +25,7 @@ namespace Avalonia.X11
         public X11Info Info { get; private set; }
         public IX11Screens X11Screens { get; private set; }
         public IScreenImpl Screens { get; private set; }
+        public X11PlatformOptions Options { get; private set; }
         public void Initialize(X11PlatformOptions options)
         {
             XInitThreads();
@@ -63,6 +65,8 @@ namespace Avalonia.X11
                 else
                     GlxGlPlatformFeature.TryInitialize(Info);
             }
+
+            Options = options;
         }
 
         public IntPtr DeferredDisplay { get; set; }
@@ -91,6 +95,7 @@ namespace Avalonia
     {
         public bool UseEGL { get; set; }
         public bool UseGpu { get; set; } = true;
+        public string WmClass { get; set; } = Assembly.GetEntryAssembly()?.GetName()?.Name ?? "AvaloniaApplication";
     }
     public static class AvaloniaX11PlatformExtensions
     {

src/Avalonia.X11/X11Window.cs

@@ -128,6 +128,8 @@ namespace Avalonia.X11
             XChangeProperty(_x11.Display, _handle, _x11.Atoms._NET_WM_WINDOW_TYPE, _x11.Atoms.XA_ATOM,
                 32, PropertyMode.Replace, new[] {_x11.Atoms._NET_WM_WINDOW_TYPE_NORMAL}, 1);
 
+            if (platform.Options.WmClass != null)
+                SetWmClass(platform.Options.WmClass);
 
             var surfaces = new List<object>
             {
@@ -873,6 +875,16 @@ namespace Avalonia.X11
             }
         }
 
+        public void SetWmClass(string wmClass)
+        {
+            var data = Encoding.ASCII.GetBytes(wmClass);
+            fixed (void* pdata = data)
+            {
+                XChangeProperty(_x11.Display, _handle, _x11.Atoms.XA_WM_CLASS, _x11.Atoms.XA_STRING, 8,
+                    PropertyMode.Replace, pdata, data.Length);
+            }
+        }
+
         public void SetMinMaxSize(Size minSize, Size maxSize)
         {
             _scaledMinMaxSize = (minSize, maxSize);