Enable native windowing system settings with SDL platform

Source/Editor/GUI/MainMenu.cs

@@ -12,7 +12,7 @@ namespace FlaxEditor.GUI
     /// <seealso cref="FlaxEngine.GUI.ContainerControl" />
     public sealed class MainMenu : ContainerControl
     {
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
         private bool _useCustomWindowSystem;
         private Image _icon;
         private Label _title;
@@ -67,7 +67,7 @@ namespace FlaxEditor.GUI
             AutoFocus = false;
             AnchorPreset = AnchorPresets.HorizontalStretchTop;
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
             _useCustomWindowSystem = !Editor.Instance.Options.Options.Interface.UseNativeWindowSystem;
             if (_useCustomWindowSystem)
             {
@@ -166,7 +166,7 @@ namespace FlaxEditor.GUI
             }
         }
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
         /// <inheritdoc />
         public override void Update(float deltaTime)
         {
@@ -291,7 +291,7 @@ namespace FlaxEditor.GUI
             if (base.OnMouseDoubleClick(location, button))
                 return true;
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
             var child = GetChildAtRecursive(location);
             if (_useCustomWindowSystem && child is not Button && child is not MainMenuButton)
             {
@@ -321,7 +321,7 @@ namespace FlaxEditor.GUI
         {
             float x = 0;
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
             if (_useCustomWindowSystem)
             {
                 // Icon
@@ -349,7 +349,7 @@ namespace FlaxEditor.GUI
                 }
             }
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
             if (_useCustomWindowSystem)
             {
                 // Buttons
@@ -367,7 +367,7 @@ namespace FlaxEditor.GUI
 #endif
         }
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
         /// <inheritdoc />
         public override void OnDestroy()
         {

Source/Editor/GUI/MainMenuButton.cs

@@ -42,7 +42,7 @@ namespace FlaxEditor.GUI
             Text = text;
 
             var style = Style.Current;
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
             if (Editor.Instance.Options.Options.Interface.UseNativeWindowSystem)
             {
                 BackgroundColorMouseOver = style.BackgroundHighlighted;

Source/Editor/Modules/UIModule.cs

@@ -381,7 +381,7 @@ namespace FlaxEditor.Modules
             Editor.Options.OptionsChanged += OnOptionsChanged;
 
             // Add dummy control for drawing the main window borders if using a custom style
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
             if (!Editor.Options.Options.Interface.UseNativeWindowSystem)
 #endif
             {

Source/Editor/Modules/WindowsModule.cs

@@ -760,8 +760,10 @@ namespace FlaxEditor.Modules
             {
                 settings.HasBorder = false;
 
+#if !PLATFORM_SDL
                 // Skip OS sizing frame and implement it using LeftButtonHit
                 settings.HasSizingFrame = false;
+#endif
             }
 #elif PLATFORM_LINUX
             settings.HasBorder = false;

Source/Editor/Options/InterfaceOptions.cs

@@ -167,7 +167,7 @@ namespace FlaxEditor.Options
         [EditorDisplay("Interface"), EditorOrder(10), Tooltip("Editor User Interface scale. Applied to all UI elements, windows and text. Can be used to scale the interface up on a bigger display. Editor restart required.")]
         public float InterfaceScale { get; set; } = 1.0f;
 
-#if PLATFORM_WINDOWS
+#if PLATFORM_WINDOWS || PLATFORM_SDL
         /// <summary>
         /// Gets or sets a value indicating whether use native window title bar. Editor restart required.
         /// </summary>