Improve tab-less dock window behavior in other platforms

Add checks for #3215 to hide the tab bar only if it doesn't prevent
window dragging in Wayland sessions with native decorations.

Source/Editor/GUI/Docking/DockPanelProxy.cs

@@ -19,11 +19,7 @@ namespace FlaxEditor.GUI.Docking
         private float _tabHeight = Editor.Instance.Options.Options.Interface.TabHeight;
         private bool _useMinimumTabWidth = Editor.Instance.Options.Options.Interface.UseMinimumTabWidth;
         private float _minimumTabWidth = Editor.Instance.Options.Options.Interface.MinimumTabWidth;
-#if PLATFORM_WINDOWS
-        private readonly bool _hideTabForSingleTab = Editor.Instance.Options.Options.Interface.HideSingleTabWindowTabBars;
-#else
-        private readonly bool _hideTabForSingleTab = false;
-#endif
+        private readonly bool _hideTabForSingleTab = Utilities.Utils.HideSingleTabWindowTabBars();
 
         /// <summary>
         /// The is mouse down flag (left button).

Source/Editor/Options/InterfaceOptions.cs

@@ -312,7 +312,7 @@ namespace FlaxEditor.Options
         public bool UseNativeWindowSystem { get; set; } = false;
 #endif
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_SDL || PLATFORM_WINDOWS
         /// <summary>
         /// Gets or sets a value indicating whether a window containing a single tabs hides the tab bar. Editor restart recommended.
         /// </summary>

Source/Editor/Utilities/Utils.cs

@@ -1571,5 +1571,19 @@ namespace FlaxEditor.Utilities
                 _ => throw new ArgumentOutOfRangeException()
             };
         }
+
+        internal static bool HideSingleTabWindowTabBars()
+        {
+#if PLATFORM_SDL
+            // We should not hide the tab bars if tab handle is the only way to dock the window
+            bool clientSideDecorations = UseCustomWindowDecorations(false);
+            bool draggableDecorations = clientSideDecorations || Platform.SupportsNativeDecorationDragging;
+            return draggableDecorations && Editor.Instance.Options.Options.Interface.HideSingleTabWindowTabBars;
+#elif PLATFORM_WINDOWS
+            return Editor.Instance.Options.Options.Interface.HideSingleTabWindowTabBars;
+#else
+            return false;
+#endif
+        }
     }
 }

Source/Engine/Platform/Base/PlatformBase.cpp

@@ -274,6 +274,15 @@ bool PlatformBase::SupportsNativeDecorations()
     return true;
 }
 
+bool PlatformBase::SupportsNativeDecorationDragging()
+{
+#if PLATFORM_LINUX
+    return false;
+#else
+    return true;
+#endif
+}
+
 #endif
 
 bool PlatformBase::Is64BitApp()

Source/Engine/Platform/Base/PlatformBase.h

@@ -379,6 +379,11 @@ public:
     /// </summary>
     API_PROPERTY() static bool SupportsNativeDecorations();
 
+    /// <summary>
+    /// Returns true if system provides support for native window dragging events.
+    /// </summary>
+    API_PROPERTY() static bool SupportsNativeDecorationDragging();
+
     /// <summary>
     /// Returns true if is running 64 bit application (otherwise 32 bit). It's compile-time constant.
     /// </summary>

Source/Engine/Platform/SDL/SDLPlatform.cpp

@@ -32,6 +32,7 @@ namespace SDLImpl
     int32 SystemDpi = 96;
     String UserLocale("en");
     bool WindowDecorationsSupported = true;
+    bool SupportsDecorationDragging = true;
     String WaylandDisplayEnv;
     String XDGCurrentDesktop;
 }
@@ -63,6 +64,8 @@ bool SDLPlatform::Init()
         SDL_SetHint(SDL_HINT_VIDEO_WAYLAND_ALLOW_LIBDECOR, "0");
         SDLImpl::WindowDecorationsSupported = false;
     }
+    if (waylandSession)
+        SupportsDecorationDragging = false;
 #endif
 
 #if PLATFORM_LINUX
@@ -204,6 +207,11 @@ bool SDLPlatform::SupportsNativeDecorations()
     return SDLImpl::WindowDecorationsSupported;
 }
 
+bool SDLPlatform::SupportsNativeDecorationDragging()
+{
+    return SDLImpl::SupportsDecorationDragging;
+}
+
 BatteryInfo SDLPlatform::GetBatteryInfo()
 {
     BatteryInfo info;

Source/Engine/Platform/SDL/SDLPlatform.h

@@ -75,6 +75,7 @@ public:
     static void Tick();
     static String GetDisplayServer();
     static bool SupportsNativeDecorations();
+    static bool SupportsNativeDecorationDragging();
     static void SetHighDpiAwarenessEnabled(bool enable);
     static BatteryInfo GetBatteryInfo();
     static int32 GetDpi();