Use a null material for non-SubEntities in the selection buffer

libs/openengine/ogre/selectionbuffer.cpp

@@ -4,6 +4,7 @@
 #include <OgreRenderTexture.h>
 #include <OgreSubEntity.h>
 #include <OgreEntity.h>
+#include <OgreTechnique.h>
 #include <stdexcept>
 
 #include <extern/shiny/Main/Factory.hpp>
@@ -100,7 +101,16 @@ namespace Render
                 return m->getTechnique(1);
             }
             else
-                throw std::runtime_error("selectionbuffer only works with entities");
+            {
+                m = Ogre::MaterialManager::getSingleton().getByName("NullMaterial");
+                if(m.isNull())
+                {
+                    m = Ogre::MaterialManager::getSingleton().create("NullMaterial", Ogre::ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME);
+                    m->getTechnique(0)->getPass(0)->setDepthCheckEnabled(true);
+                    m->getTechnique(0)->getPass(0)->setDepthFunction(Ogre::CMPF_ALWAYS_FAIL);
+                }
+                return m->getTechnique(0);
+            }
         }
         return NULL;
     }