Ubuntu bionic and ogre2

[diegoferigo]

The default rendering engine of Ignition Gazebo is ogre-next (previously known as ogre2).

On my setup, that is Ubuntu Bionic running in a docker container with Nvidia support, the ogre2 backend cannot find a recent enough version of OpenGL and Ignition GUI segfaults.

There are two possible workarounds:

• Specify ogre2 as default engine in your world file
• Edit $HOME/.ignition/gazebo/gui.config and change:

--- .ignition/gazebo/gui.config 2020-06-04 14:41:33.471804733 +0200
+++ .ignition/gazebo/gui.config 2020-06-04 14:42:47.826475035 +0200
@@ -30,7 +30,7 @@
     <property type='bool' key='showTitleBar'>false</property>
     <property type='string' key='state'>docked</property>
   </ignition-gui>
-  <engine>ogre2</engine>
+  <engine>ogre</engine>
   <scene>scene</scene>
   <ambient_light>0.4 0.4 0.4</ambient_light>
   <background_color>0.8 0.8 0.8</background_color>

We should add this information in a Troubleshooting or FAQ section of the website.

For future reference, here is the error I get (it would happen also with the upstream command ign gazebo):

gym-ignition on  devel [$!?] via 🐍 v3.6.9 (venv) 
✦ ❯ python examples/python/launch_cartpole.py 
WARN: Box bound precision lowered by casting to float32
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-dferigo'
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:732]  Unable to create the rendering window
[GUI] [Err] [Ogre2RenderEngine.cc:739] Unable to create the rendering window