While Tron has about 15 minutes of CGI, this 1984 film which also included a video game as a crucial plot point was the first to have entire scenes that were entirely virtual with an attempt to create real objects with integrated CGI. It was the first feature film to replace spacecraft models with virtual constructs. Will Wheaton has a small role in this film, while Robert Preston's performance as Centauri is clearly a nod to his Harold Hill role in The Music Man.
The Last Starfighter