Do the devs need to rewrite the game? Or is the source code there and waiting to be compiled again with newly made graphics?<p>Obviously the answer is partly "it depends", but interested to hear some facts.
Usually, porting it to an improved version of the engine.<p>When the game is in development the engine is branched and changes happen to accommodate the new game, if you are good about keeping the engine separate from the game then the branch is just to keep things stable, but you'll always have to customise it a little.<p>Your engine team keep working on the engine for new games, graphics improve, optimisations for new hardware, lighting, etc;etc;etc;<p>What you need to do is go through all the old content and ensure it has higher resolution bitmaps for all textures, and then port it to the new engine. It sounds simple, but it's really not.<p>P.S: I work for ubisoft but I have never been involved with a game remaster, so this is just my perception of how it would be done.