After watching Furious 7, I was amazed that throughout the movie I didn't feel that Paul Walker didn't complete the film but yet his presence is not felt anything like virtually created. How was this actually? 

I heard that his brother was taken for some shots and a body double was used but some articles say that his body and face is computer generated. It feels so real. So did we make enough advancement in cinematography that we can now virtually create real people through CGI?