In practice you need a global coordinate system. For example, you'd create a "spawn point" for all players, and then, before the game starts, move them to their starting positions at a fraction of c. The game is still keeping track of units within this initial coordinate system, and transform those coordinates for the player. The reverse is done for player decisions. There is effectively an in-game "star network" that mediates between player. Each player/unit has a unique light cone associated with it.
Nothing stops us from arbitrarily designating a particular reference frame as "preferred" in a simulation; SR merely says that such a choice is truly arbitrary. Note also that this system could work recursively, such that new units must always spawn at the spacetime location of older units, and do information management (behind the scenes) in a similar way. This would turn the network into a tree - and the transforms are relatively cheap (and we could use a Spacetime algebra library!)
Note that I don't think this works for a traditional RTS like C&C or Supreme Commander. But rather a game like Civilization, but galaxy spanning (and spanning very long periods of time), where the smallest objects are something like "suns" and "fleets". The individual lives of humans would come and go as these vast battles took place over thousands of years. You'd only need to add magic like a 1g constant acceleration drive - and a strong rule against using this to directly kill planets - and assume that the fleets are actually large-ish asteroids fitted with the drives and a human and/or robotic crew.
Nothing stops us from arbitrarily designating a particular reference frame as "preferred" in a simulation; SR merely says that such a choice is truly arbitrary. Note also that this system could work recursively, such that new units must always spawn at the spacetime location of older units, and do information management (behind the scenes) in a similar way. This would turn the network into a tree - and the transforms are relatively cheap (and we could use a Spacetime algebra library!)
Note that I don't think this works for a traditional RTS like C&C or Supreme Commander. But rather a game like Civilization, but galaxy spanning (and spanning very long periods of time), where the smallest objects are something like "suns" and "fleets". The individual lives of humans would come and go as these vast battles took place over thousands of years. You'd only need to add magic like a 1g constant acceleration drive - and a strong rule against using this to directly kill planets - and assume that the fleets are actually large-ish asteroids fitted with the drives and a human and/or robotic crew.
The spawn point would then be, fittingly, Sol.