Try to use the VirtualGL's EGL backend

Dockerfile.m4

@@ -450,7 +450,6 @@ ENV UNPRIVILEGED_USER_SHELL=/bin/bash
 ENV XRDP_TLS_KEY_PATH=/etc/xrdp/key.pem
 ENV XRDP_TLS_CRT_PATH=/etc/xrdp/cert.pem
 ENV ENABLE_XDUMMY=false
-ENV VGL_DISPLAY=:0.0
 ## Use Adwaita theme in QT applications
 ENV QT_STYLE_OVERRIDE=Adwaita
 

README.md

@@ -48,7 +48,7 @@ encounter any problem related to this you may use the `--shm-size` option.
 * `UNPRIVILEGED_USER_PASSWORD`: unprivileged user password (`password` by default).
 * `UNPRIVILEGED_USER_GROUPS`: comma-separated list of additional GIDs for the unprivileged user (none by default).
 * `UNPRIVILEGED_USER_SHELL`: unprivileged user shell (`/bin/bash` by default).
-* `ENABLE_XDUMMY`: enable an X dummy server (`false` by default).
+* `ENABLE_XDUMMY`: enable a dummy X server (`false` by default).
 
 ## License
 

config/skel/.xsessionrc

@@ -11,6 +11,6 @@ export XDG_RUNTIME_DIR=/run/user/${UNPRIVILEGED_USER_UID:?}
 export XDG_SESSION_DESKTOP=xubuntu
 export XDG_SESSION_TYPE=x11
 
-if [ "${ENABLE_XDUMMY:?}" != 'true' ]; then
+if [ -z "${VGL_DISPLAY-}" ] && [ -n "${DISPLAY-}" ]; then
 	export VGL_DISPLAY=${DISPLAY:?}
 fi

scripts/bin/container-init

@@ -60,6 +60,22 @@ if [ "${ENABLE_XDUMMY:?}" = 'true' ]; then
 	ln -s /etc/sv/xdummy /etc/service/
 fi
 
+# Define VGL_DISPLAY variable if it is not set
+if [ -z "${VGL_DISPLAY-}" ]; then
+	# Use the dummy X server if it is enabled
+	if [ "${ENABLE_XDUMMY:?}" = 'true' ]; then
+		export VGL_DISPLAY=:0.0
+	# Otherwise try to use the EGL backend
+	else
+		for card in /dev/dri/card*; do
+			if /opt/VirtualGL/bin/eglinfo -B "${card:?}" 2>/dev/null; then
+				export VGL_DISPLAY=${card:?}
+				break
+			fi
+		done
+	fi
+fi
+
 # Create RANDFILE if it does not exist
 RANDFILE=${RANDFILE-${HOME:?}/.rnd}
 if [ ! -f "${RANDFILE:?}" ] && [ -c /dev/urandom ]; then