Save Nonvisual Game Replay

[irishninja]

I am currently looking at experimenting with different AIs and would like to be able to run different experiments headlessly then be able to watch/demo selected replays. I have noticed that 0 AD currently does not support saving replays when nonvisual and it seems largely due to a reliance on GetSimulationState (from the GuiInterface). 

I haven't yet dug deeply enough to be able to see how difficult it would be to refactor the code so GetSimulationState does not relay on the GUI (I am a bit concerned about some of the calls to `QueryInterface` which I haven't yet dug into). Does this seem feasible? If so, I would appreciate any pointers or suggestions. 

Also, if I am able to make this change, would 0 AD be willing to uptake this or would it only live in my fork?

[Stan`]

I guess it's because we do not serialise AI commands 

You could use this patch https://code.wildfiregames.com/D153

You could also finish it it following Itms comments

If your changes are good we will try to get them in our engine

[bb_]

When you are using AI's it is quite easy to achieve this: AI do not print (at least currently) anything in the command.txt except on the first line (that line gives match settings, further the replay is empty). So all you have to do is create some of those "first lines" (I guess you want to test the AI on a couple of times on the same map, for that you just need to change the seeds, such that every game is different) and put as many empty turns as you like afterwards, which will give you the wanted replays. (In principle you don't even need to have run to game to already have the "replay" ;))

[irishninja]

Thanks for the quick replies!  

@stanislas69 I have been digging into it a little bit more and it seems that the main call that fails is `getReplayMetadata` (which generates the metadata.json file saved for the replays). It seems that without the metadata.json, the replay doesn't show up in the replay list so I figured it was a file that I needed. Currently, that file will not be generated if it is running in nonvisual mode and overriding this manually results in an error since it seems the `getReplayMetadata` command can only be called from the script interface used by g_GUI (not available if running in nonvisual). Does that make sense?

I actually am a fan of the way the AI is treated during replays :). Although it is different from the humans, expecting the AI to be deterministic (and controlling the random seed) is cool since we could hypothetically resume a replay at any point (if it is player vs bot) and the bot would adapt accordingly. If it was simply replaying fixed actions (and not recomputing the AI's behavior), this wouldn't be possible. This feature isn't available now (afaik) but would be cool when exploring things like imitation learning.

Awesome to hear that you are open to contributions! I am interested in using 0 AD as an RL sandbox but would like to keep any fork as small as possible since maintaining forks is no fun. If possible, it would be really great if all RL experimentation related features could be added to 0 AD itself (and toggled with cli options to not change any of the current behavior, of course)  .

@bb_ and @stanislas69 I have actually been working on my own fork where I am exposing a GRPC interface to the game for controlling the player (actions are then logged to the replay - at least when there is a GUI). It is still a work in progress; I can currently control units and issue player commands but still need to add support for some other features like loading a scenario (maybe defined dynamically), saving replays when nonvisual, and smooth GUI movements when watching an RPC-controlled game.

[irishninja]

In case anyone is following this thread, there is currently a ticket opened (and patch submitted with the update!): https://code.wildfiregames.com/D2197 and https://trac.wildfiregames.com/ticket/5565