I've been dealing with some frame-rate jittering issues with my game lately, and it seems that the best solution would be the one suggested by Glenn Fiedler (Gaffer on Games) in the classic Fix Your Timestep! article.
Now - I'm already using a fixed time-step for my update. The problem is that I'm not doing the suggested interpolation for rendering. The upshot is that I get doubled or skipped frames if my render rate doesn't match my update rate. These can be visually noticeable.
So I'd like to add interpolation to my game - and I'm interested to know how others have structured their data and code to support this.
Obviously I will need to store (where?/how?) two copies of game state information relevant to my renderer, so that it may interpolate between them.
Additionally - this seems like a good place to add threading. I imagine that an update thread could work on a third copy of the game state, leaving the other two copies as read-only for the render thread. (Is this a good idea?)
It seems that having two or three versions of the game's state could introduce performance and - far more importantly - reliability and developer productivity problems, compared to having just a single version. So I'm particularly interested in methods for mitigating those issues.
Of particular note, I think, is the problem of how to handle adding and removing objects from the game state.
Finally, it seems that some state is either not directly needed for rendering, or would be too difficult to track different versions of (eg: a third-party physics engine that stores a single state) - so I'd be interested to know how people have handled that kind of data within such a system.