Saved Games, the Universe, and Everything

So, the point has been raised several times on how saved games will work. The point has also been raised as to how the galaxy generation will work. Although the main focus of this thread is on saves, I think it's inevitable we will have to cover generating galaxies as that is the setting of the player's saves.

Now, there are two conceivable systems I can imagine us using for handling galaxy generation and saves in Thrive. The first is generating a single galaxy and using a linear system of saves. The way this works is that the galaxy is generated and the player starts to play in it, and when they are finished they save, leave, and when they come back resume from that save. Then, when they save for a second time, they have no choice but to replace their old save. This means you make a single game split into two separate saves that are taking place in different galaxies, since only one galaxy is ever generated. What this means is that you can save, try something out, and then if you fail load the last save and try again. However, you cannot save a game at a certain point, then play the game along one path, create a separate save for that path, and then come back and try a different route of gameplay from the older save. Basically, each species' playthrough you do has its own save slot, and no more. The reason for all this restriction is because it all takes place within one, continuously progressing galaxy.

Games with similar systems: The Sims, Sim City, Mount and Blade

Pros:
-Saves an immense amount of space by only having to generate one galaxy.
-Allows for potential interaction between species across saves
Cons:
-Does not allow for differing save-paths from the same point in a playthrough
-Allows for potential interaction between species across saves

The second system we could use is the more common multi-save system, where you can theoretically have as many saves as you want and there is no conflict between them whatsoever, because they all take place in alternate universes. This would mean that a new galaxy would have to be generated at the beginning of each new playthrough. It would also mean that the player could create as many differing saves as they wanted for the same species/playthrough.

Games with similar systems: Sid Meier's Civilization, The Elder Scrolls, Rollercoaster Tycoon

Pros:
-No restrictions on saving.
Cons:
-Immense space required to store the multiple galaxies that must be generated.

These are just some ideas I have off the top of my head of different approaches to save systems/game world generation that we can consider. I think it's necessary that we go with the first system because of memory restraints, but I'd like to hear other ideas on how to address this.

We could have a mix of both, each save is a galaxy and there are other saves inside the galaxy save that are like the second example.

Oh, what's this? I see a myth to dispel!

I've always assumed that the galaxy will be generated in as lazy a manner as possible -- that is, any time something must be created and written to file, we endeavor to do that as late as possible. As a consequence, the save for a galaxy would only contain some PCG metadata (for generating the bits of the galaxy that haven't been modified yet), and some patching system to apply player-made modifications. This way, we pretty much minimize disk data (and bandwidth needed when loading), at the cost of processing power regenerating places you visit over and over.

Some important details:

• The metadata would have to include the version info for the procedural generator system, at least, if we want to maintain backwards compatibility (by choosing a generator to match the save version at load time)
  
• The granularity of the patching system could be adjusted to put you anywhere on the memory-cheap<->processing-cheap spectrum -- one end being the extreme I detailed above, the other end being the case where the whole galaxy is generated and saved to disk in one fat file. We probably want something in the middle, closer to the memory-cheap side.
  

So there we have it -- with some clever programming, galaxies need not take massive storage space.

With that out of the way, which would I prefer? No idea.

If the save file for a galaxy would really be that small, then I am completely in favour of having separate galaxies per save, instead of everything taking place in one galaxy. Having everything take place in the same galaxy would produce many complications when the species interact and are across stages, or when one species is being played and other saves must either progress simultaneously, or freeze in time as a separate save is being played.

It's going to be possible, but very technically complicated. For example, we'd likely have to make super-auto-evo deterministic, or we'll have to save each living planet when you first encounter it. I'm pretty darn sure that super-auto-evo will be very sensitive to initial conditions, and when you mix that in with floating-point indeterminism and so on, we'll probably have to save anything alive on first encounter. And then there's the thorny problem of other civs, on other planets, beating you to space. If we don't sim planets until you first encounter them, then all you'll ever encounter are one-planet species. It's possible that the best answer to these problems is to save much more of the galaxy than I thought. I'm not sure, I'd have to think about it.

Multiple galaxies seem a better option initially, as the method for simulating multiple saves in a single galaxy looks too complex to worry about until we can afford to. Anyway, this isn't realistically going to affect anything until we actually reach the later stages.

True, as we discussed it I realized that since we can progressively develop the start-up settings and generation, this won't be as important now as we focus on microbial generation. However, concept-wise I think we'll settle with each playthrough taking place in a separate galaxy, not all in one like Spore.