Launch on xwayland under Wayland if no EGL

On initialization, if wxWidgets was compiled without EGL support, check
in environment variables if running under Wayland and if so tell GDK to
prefer using an X11 backend, causing the program to launch under
xwayland.

Fix #1028

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

src/wx/wxvbam.cpp

@@ -47,6 +47,10 @@
 #include "widgets/user-input-ctrl.h"
 #include "wxhead.h"
 
+#ifdef __WXGTK__
+#include <gdk/gdk.h>
+#endif
+
 namespace {
 
 // Resets the accelerator text for `menu_item` to the first keyboard input.
@@ -136,6 +140,15 @@ int main(int argc, char** argv) {
     wxLog::SetLogLevel(wxLOG_Info);
 #endif  // DEBUG
 
+    // Launch under xwayland on Wayland if EGL is not available.
+#if defined(__WXGTK__) && !defined(HAVE_WAYLAND_EGL)
+    wxString xdg_session_type = wxGetenv("XDG_SESSION_TYPE");
+    wxString wayland_display  = wxGetenv("WAYLAND_DISPLAY");
+
+    if (xdg_session_type == "wayland" || wayland_display.Contains("wayland"))
+        gdk_set_allowed_backends("x11,*");
+#endif
+
     // This will be freed on wxEntry exit.
     wxApp::SetInstance(new wxvbamApp());
     return wxEntry(argc, argv);