Fix various issues with child window positioning

Source/Engine/Platform/SDL/SDLPlatform.Linux.cpp

@@ -30,6 +30,7 @@ Delegate<void*> LinuxPlatform::xEventReceived;
 namespace
 {
     bool UseWayland = false;
+    bool UseXWayland = false;
     X11::Display* xDisplay = nullptr;
     X11::XIM IM = nullptr;
     X11::XIC IC = nullptr;
@@ -847,7 +848,12 @@ bool SDLPlatform::InitPlatform()
         return true;
 
     if (!CommandLine::Options.Headless)
+    {
         UseWayland = strcmp(SDL_GetCurrentVideoDriver(), "wayland") == 0;
+        String waylandDisplay;
+        if (/*!UseWayland &&*/ !Platform::GetEnvironmentVariable(TEXT("WAYLAND_DISPLAY"), waylandDisplay))
+            UseXWayland = waylandDisplay.Length() > 1;
+    }
 
     return false;
 }
@@ -920,7 +926,7 @@ bool SDLPlatform::UsesWayland()
 
 bool SDLPlatform::UsesXWayland()
 {
-    return false;
+    return UseXWayland;
 }
 
 bool SDLPlatform::UsesX11()