Thanks for your quick reply. Do you know how to do that? Or where could I get some example for that?
Just change the current OpenGL view matrix before the call of GLC_World::render(...);
Something like that :
glScaled(NewPlaneNormal.x, NewPlaneNormal.y, NewPlaneNormal.z);
glTranslated(PointOnTheMirrorPlane.x, PointOnTheMirrorPlane.y, PointOnTheMirrorPlane.z);
To create shadow effect, you can disable lightning before rendering the mirror.
Tips : mirror must be render before normal scene...
Recommended reading : More OpenGL Game Programming
It's not a GLC_lib built-in function... It's a pure OpenGL.