However, the animations in Tron were produced individually frame by frame as strictly 2D generated imagery rather than as a continuously animated motion sequence (that is to say, each frame was rendered as a static image rather than from computer generated models with algorithmically controlled motion) and was almost exclusively used for distance shots. There was not ability at the time to digitize (with adequate resolution) and composite en scene any kind of footage with human figures so all of the animated scenes are separate from any filmed scenes, and it shows.
Star Trek II: The Wrath of Khan arguably has the first and longest (somewhat) photorealistic animation for the time when Kirk and crew view the classified video of the Genesis Project (as opposed to wireframe animation overlays such as in Return of the Jedi), although it is intended in the film to be a computer-generated simulation. This wasn’t the first such animation—Lucasfilm had done similar CGI animations for JPL—but probably the first in a feature film.
The Last Starfighter is generally taken to be the first fully CGI ‘photorealistic’ animated scenes of ‘live action’ (that is, scenes that actually occur in the world of the film rather than as a simulation within it), and comprise a significant amount of screen time as all of the space battle sequences. They’re pretty bad by modern standards and basically look like first pass rendering of crudely faceted models but it did actually use ray tracing to get shadows and reflections correct rather than as a ‘flat’ image or simple primitives.
Young Sherlock Holmes (already mentioned) was the first fully digitally composited feature film with interactive live action and CGI elements, and The Flight of the Navigator (an otherwise forgettable movie) was the first with reflective composited CGI. By the late ‘Eighties CGI had become an industry onto its own right and completely photorealistic compositing with sophisticated optical effects and motion capture like that in The Abyss were possible (with enough budget and James Cameron-like obsessiveness to detail).
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