Thank you for your answers.
I have told about cylinder just for example, so I have no problem of rotation.
In my case, I don’t know if two solids will be the same in the same position.
I have solved my problem by using glPolygonOffset() as you have suggested.
Thanks a lot.
The cylinder gets triangulized and so rotation gets important again.
I wanted to answer to superposition, not to create a new topic.
The button you wanted to use is called “post reply” and can be clicked inside the discussion you want to reply to. Hope that helps.