ondras
commented
2 years ago Hi @Gerhard-Wonner,
thanks for the bugreport. You are not the only one running into these mysterious desyncs: it has been reported recently (see https://github.com/ondras/rot.js/issues/201).
The issue is puzzling though, because the RNG itself is very simple and there are not many places where stuff could go wrong. I reviewed the code many times - and while the math aspect is out of my league (the underlying algorithm was provided by a real mathematician), managing the state and seeding is very straightforward. So even if we managed to reduce and find the core cause of the behavior, fixing it might be a completely different beast.
To further analyze the problem, I would suggest the following:
1) are you executing your JS server-side or client-side? If client-side, are you always using the same os/browser?
2) are you certain there are no un-controlled accesses to your RNG? The ROT.RNG object is used in a singleton-like manner in many places throughout the rot.js code, so it might be better to create a separate instance (via clone() and pass it around). You can then invalidate the global RNG (by some rogue assignment like ROT.RNG.getUniform = console.error) and see whether there si some code path using it accidentaly.
3) do you have a particular seed that always exhibits a desync? If so, we might simply try generating a very large number of random values and comparing the final value/state.
For instance, I just created a small testbed at https://jsfiddle.net/ondras/0Lgxbotw/. Here is what it shows on my Firefox:
Does your environment result in identical values?
Gerhard-Wonner
Hello @ondras,
I implemented a replay-mode in my game. Therefore I store the seed of the game into the database together with the sequence of all the keystrokes of the player. The replay works quite well in most cases. :-)
My problem is: It works in most cases, but it does not work in all cases! :-( Sometimes I realize that the replay diverges from the true game from a certain point (sometimes after thousands of turns). In most cases this results in the player-character eventually running into a wall. In rarer cases the whole level is generated in a different way.
I already separated the random value generation to different instances of the generator to keep the generation clean. E.g. I randomize the music from time to time, which I do with a separate instance of the randomizer. The remaining calls of the main-randomizer should now be time-independent and completely deterministic (with a given seed).
This is a very severe problem to me since I have no idea how to debug it. I tried a lot of things including logging the RNG-state and recording the game while playing and comparing it to the replay afterwards. My problem is, there is just too much information to keep track of. Logging everything is just not possible.
I am just a hobbyist and no professional JavaScript-developer, so I do not know many tricks or tools. Maybe there is a debugging tool out there, that could help me?
How would you approach this thing?
Thank you for your help!
Kind regards Gerhard