Fix an issue that if WindowState is been set in the constructor, the contents that not been layouted or rendered will be shown.

src/Avalonia.X11/X11Window.cs

@@ -686,7 +686,7 @@ namespace Avalonia.X11
                     ChangeWMAtoms(false, _x11.Atoms._NET_WM_STATE_FULLSCREEN);
                     ChangeWMAtoms(true, _x11.Atoms._NET_WM_STATE_MAXIMIZED_VERT,
                         _x11.Atoms._NET_WM_STATE_MAXIMIZED_HORZ);
-                    MapWindow();
+                    MapOrActiveWindow();
                 }
                 else if (value == WindowState.FullScreen)
                 {
@@ -694,7 +694,7 @@ namespace Avalonia.X11
                     ChangeWMAtoms(true, _x11.Atoms._NET_WM_STATE_FULLSCREEN);
                     ChangeWMAtoms(false, _x11.Atoms._NET_WM_STATE_MAXIMIZED_VERT,
                         _x11.Atoms._NET_WM_STATE_MAXIMIZED_HORZ);
-                    MapWindow();
+                    MapOrActiveWindow();
                 }
                 else
                 {
@@ -702,7 +702,7 @@ namespace Avalonia.X11
                     ChangeWMAtoms(false, _x11.Atoms._NET_WM_STATE_FULLSCREEN);
                     ChangeWMAtoms(false, _x11.Atoms._NET_WM_STATE_MAXIMIZED_VERT,
                         _x11.Atoms._NET_WM_STATE_MAXIMIZED_HORZ);
-                    MapWindow();
+                    MapOrActiveWindow();
                 }
                 WindowStateChanged?.Invoke(value);
             }
@@ -1206,33 +1206,38 @@ namespace Avalonia.X11
 
         }
 
-        /// <summary>
-        /// Map the window to the screen.
-        /// </summary>
-        /// <remarks>
-        /// Why we map the window using XMapRequestEvent instead of XMapWindow or SendNetWMMessage?<br/>
-        /// See details at https://github.com/AvaloniaUI/Avalonia/pull/16922
-        /// </remarks>
-        private void MapWindow()
+        private void MapOrActiveWindow()
         {
-            var e = new XEvent
+            if (_wasMappedAtLeastOnce)
             {
-                MapRequestEvent = new XMapRequestEvent
+                // If the window has been mapped at least once, we should use XMapRequestEvent instead of XMapWindow or SendNetWMMessage.
+                // See details at https://github.com/AvaloniaUI/Avalonia/pull/16922
+                var e = new XEvent
                 {
-                    type = XEventName.MapRequest,
-                    serial = new IntPtr(0),
-                    display = _x11.Display,
-                    send_event = 1,
-                    parent = _x11.RootWindow,
-                    window = _handle,
-                },
-            };
-            XSendEvent(
-                _x11.Display,
-                _x11.RootWindow,
-                false,
-                new IntPtr((int)EventMask.SubstructureRedirectMask),
-                ref e);
+                    MapRequestEvent = new XMapRequestEvent
+                    {
+                        type = XEventName.MapRequest,
+                        serial = new IntPtr(0),
+                        display = _x11.Display,
+                        send_event = 1,
+                        parent = _x11.RootWindow,
+                        window = _handle,
+                    },
+                };
+                XSendEvent(
+                    _x11.Display,
+                    _x11.RootWindow,
+                    false,
+                    new IntPtr((int)EventMask.SubstructureRedirectMask),
+                    ref e);
+            }
+            else
+            {
+                // If the window has never been mapped, we should send _NET_ACTIVE_WINDOW message.
+                // Otherwise, the window will show too early so that content that not been layouted or rendered will be shown.
+                SendNetWMMessage(_x11.Atoms._NET_ACTIVE_WINDOW, (IntPtr)1, _x11.LastActivityTimestamp,
+                    IntPtr.Zero);
+            }
         }
 
         private void BeginMoveResize(NetWmMoveResize side, PointerPressedEventArgs e)