In movie vfx there are probably two routes open to you: R&D Programming, or Technical Director. R&D tend to develop blue sky research, brand new tools and cutting edge techniques. These can take the form of standalone programs or plugins integrated into any of the major packages (Houdini, Maya etc). A senior R&D guy would for example look at a research paper coming out of SIGGRAPH and implement it for use at their company. (Or would come up with the new research and present it at Siggraph!) Junior R&D would involve more tools maintenance, adding new features as requested by the needs of production, writing pipeline tools to improve workflows etc.

TDs usually work directly on shots for films. To do this work you also have to be able to use one or more of the major packages, people from CS backgrounds tend to gravitate towards FX TD positions - making particle systems, running fluid dynamics sims, generating procedural models or textures. Being able to program and problem solve is a key skill for these roles, but you would also have to prove yourself visually to get into a position here - create a showreel that shows off some awesome images your technical skills have allowed you to create.

The more hardcore a programmer you are, the more likely you'd be to end up in R&D. The more knowledge you have of software packages, and how much you enjoy creating images, would make you more likely to end up in production as some sort of TD.

Doing a graphics related PhD is the sure firest way of getting in the door as R&D, doing something like an MSc in Computer Animation (e.g. Bournemouth in the UK does a 1 yr course) would speed up entry to being a super useful TD, or a really useful R&D guy (there's a lot to be said for R&D having mucho knowledge of the relevant production software).