#How to use random?

1 messages · Page 1 of 1 (latest)

high locust
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I have read that I should be adding Randoms to each entity that needs any random-ness. To be honest, that does not feel easily controllable to me. I'd rather just have one global random rng, or at least one per system. Is there a reason for Unity choosing the rng-per-entity approach, am I shooting myself in the foot?

scarlet lodge
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I don't recall unity ever recommending random per entity, if you have a source of be interested in reading

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As for global random, doesn't really work as it's not thread safe

high locust
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The youtube channel "turbo makes games" recommends it in one of his videos

scarlet lodge
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So a YouTuber suggests it

high locust
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Allthough I have no idea if thats a valid source, he mostly just reads out the unity tutorials in a video format

scarlet lodge
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Anyway you could have a global seed to generate per thread randoms in systems

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Per entity random has some advantages though in that it's deterministic etc

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But it also creates a giant dependency mess in your code

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Which I am pretty against

high locust
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How is per entity more deterministic than per-system?
I can just have one per system, I seed new ones per job and that should be deterministic or not

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ah it isn't because the order is not deterministic?

scarlet lodge
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It's more that you need per thread not per system

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If you seed a job with a single random every thread will produce the same values

high locust
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ah yeah ofc

scarlet lodge
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A simple way around this is something like Random.FromIndex(seed + entity.index)

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Or better yet using chunk index in a ijc

high locust
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so I just pass the seed to the job?, and then seed a new random not even in every thread but for every entity?

scarlet lodge
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I've seen half a dozen ways of doing this

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None yet that have clearly been the best to me

high locust
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why can't one just pass in an array of rngs, one per thread?

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is the number of threads not deterministic?

scarlet lodge
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Totally doable

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That's a way I've seen done as well

high locust
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that would basically be how you do it in the machine learning frameworks I know

scarlet lodge
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Thread based random is not deterministic though

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But most games don't care

grim oxide
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is there a way to obtain thread id in a job?

scarlet lodge
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Yes

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[NativeSetThreadIndex]

grim oxide
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then I guess you can just write wrapper in native reference

scarlet lodge
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Or something like that

grim oxide
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and pass to jobs when you need it

high locust
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why is thread based random not deterministic? Since the assignment "thread <-> entities it operates on" is not deterministic?

scarlet lodge
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Yeah

grim oxide
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but honestly, that sounds like a slow one

scarlet lodge
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Repeat it multiple times and your chunks won't end up on same threads

scarlet lodge
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You avoid need to hash seed per entity

grim oxide
high locust
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ok, so per-entity randomness actually is the only way to make it determinstic then, right? Or the thing you said with seeding with entity-id

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otherwise due to the non-deterministic thread-id working on your entities you have no chance?

grim oxide
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which would be double random access

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first to thread map, then to random itself

scarlet lodge
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You do it once per chunk

scarlet lodge
grim oxide
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yeah, but how would you do it with IJE?

high locust
scarlet lodge
grim oxide
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wait what?

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they implemented that?

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damn

scarlet lodge
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Yeah Dani did it for me in pre 15

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Best thing ever added

grim oxide
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all right all right

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and here I was dreaming about it just yesterday

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😅

scarlet lodge
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Been in for months!

grim oxide
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I haven't really used entities

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in more than a month

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stuck with webgl quest game

high locust
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Thank you for the help!

vague marten
remote condor
high locust