Prefer GLFW X11 backend when no Wayland display is set

[lgulich]

Summary

Inside Docker, ros2_control_node prints a spurious error twice at startup:

[MujocoSimulation]: Initializing simulation...
error: XDG_RUNTIME_DIR is invalid or not set in the environment.      # viewer glfwInit()
...
error: XDG_RUNTIME_DIR is invalid or not set in the environment.      # CameraPlugin glfwInit()
[MujocoSystemInterface]: Auto-registered plugin: mujoco_ros2_control_plugins/CameraPlugin

GLFW >= 3.4 built with both Wayland and X11 (e.g. Bazel builds using BCR glfw 3.4.0) falls back to probing platforms in order when XDG_SESSION_TYPE is unset, and Wayland comes first. libwayland prints the error, then GLFW falls back to X11 and everything works.

The core library and libmujoco_ros2_control_plugins_impl.so can each carry their own statically linked GLFW, so the init hint must be set from both:

+mujoco_ros2_control_plugins/glfw_platform.hpp
+  static inline prefer_x11_without_wayland_display()
+    if GLFW >= 3.4 && !WAYLAND_DISPLAY && X11 supported
+      glfwInitHint(GLFW_PLATFORM, GLFW_PLATFORM_X11)

 MujocoSimulation::initialize
+  prefer_x11_without_wayland_display()
   GlfwAdapter -> glfwInit()              # viewer
 CameraPlugin::init
+  prefer_x11_without_wayland_display()
   glfw_init_fn()                         # cameras

Compiled out on GLFW < 3.4 (Ubuntu's system libglfw3 3.3 is X11-only anyway).

Evidence

Bazel build of unitree_g1_bringup unitree_g1_controller_manager.launch.py hardware_type:=mujoco initial_controller_group:=agile_velocity, env stripped like a container (env -u XDG_RUNTIME_DIR -u XDG_SESSION_TYPE -u WAYLAND_DISPLAY), real X display:

• Before: grep -c 'XDG_RUNTIME_DIR is invalid' → 2 (viewer + camera plugin)
  After: grep -c 'XDG_RUNTIME_DIR is invalid' → 0; viewer starts, camera rendering loop starts, controllers switch successfully.

Also verified in a release-2026.09 isaac-ros activate container (Ubuntu 24.04, ROS_DISTRO=lyrical, no XDG_RUNTIME_DIR/XDG_SESSION_TYPE/WAYLAND_DISPLAY) with ros-lyrical-unitree-g1-bringup installed from the release snapshot, running the tutorial launch command:

• Before (released ros-lyrical-mujoco-ros2-control{,-plugins}): XDG_RUNTIME_DIR is invalid → 2
  After (same packages rebuilt with this change): → 0; controllers switch successfully in both runs.

pre-commit passes.

Merge Danger

Door: two-way

Blast Radius: small

Only affects GLFW platform selection when WAYLAND_DISPLAY is unset. Real Wayland sessions (which set WAYLAND_DISPLAY) keep GLFW's default auto-detection.

🤖 Generated with Claude Code