Enforce xcb platform on Wayland (#1850)

Wayland support for Ogre was only added in version 14.
Thus, when running on Wayland with older Ogre, we need to explicitly enforce Qt's xcb platform protocol, essentially running X11 through Xwayland.

Backported with adaptations from ros2/rviz#847.

Author: v4hn

src/rviz/main.cpp

@@ -28,11 +28,35 @@
  */
 
 #include <QApplication>
+#include <QProcessEnvironment>
 
 #include <rviz/visualizer_app.h>
 
 int main(int argc, char** argv)
 {
+#if !OGRE_USE_WAYLAND
+  // If Ogre does not support wayland, but we are running on wayland,
+  // explicitly enforce the xcb platform for Qt unless the user set the platform
+  std::vector<char*> args;
+  for (int i = 0; i < argc; ++i)
+  {
+    args.push_back(argv[i]);
+  }
+
+  auto env = QProcessEnvironment::systemEnvironment();
+  if (env.value("XDG_SESSION_TYPE") == "wayland" &&
+      std::find(args.begin(), args.end(), "-platform") == args.end() && // no -platform arg
+      !env.contains("QT_QPA_PLATFORM"))                                 // no env setting of platform
+  {
+    std::cout << "Enforcing xcb platform instead of wayland." << std::endl;
+    static const char* xcb_platform_args[] = {"-platform", "xcb"};
+    args.push_back(const_cast<char*>(xcb_platform_args[0]));
+    args.push_back(const_cast<char*>(xcb_platform_args[1]));
+    argc = static_cast<int>(args.size());
+    argv = args.data();
+  }
+#endif
+
   QApplication qapp(argc, argv);
 
   rviz::VisualizerApp vapp;