HP has a cool series of documentaries up on its site that detail the use of CGI for BB-8 in Star Wars: The Force Awakens. There are a few times BB-8 is CGI and no one noticed. In all there are three documentaries up on the site.
The second one is about the X-wing’s CGI work:
The third doc is about the Falcon in the Star Destroyer graveyard chase:
Note: When you watch the first doc, under it you will see the other docs to watch there. They’re pretty cool!