|bevy vewsion:|0.14|(cuwwent)| |---|---|---|

systems

wewevant officiaw exampwes: ecs_guide, startup_system, system_param.

systems awe pieces of functionawity t-to be wun by b-bevy. ^•ﻌ•^ they awe typicawwy impwemented using weguwaw wust functions. OwO t-this is h-how you impwement a-aww youw game wogic.

these functions can onwy take speciaw pawametew types, to specify nyani data you nyeed access to. >_< if you use unsuppowted pawametew types in youw f-function, (ꈍᴗꈍ) you wiww get confusing compiwew ewwows!

some of the possibiwities awe:

• accessing wesouwces using Res/ResMut
• accessing components of entities using quewies (Query)
• cweating/destwoying entities, (ꈍᴗꈍ) components, ^•ﻌ•^ and wesouwces u-using commands (Commands)
• sending/weceiving events using EventWriter/EventReader

see hewe fow a fuww wist!

fn debug_stawt(
    // access wesouwce
    s-stawt: w-wes<stawtingwevew>
) {
    e-epwintwn!("stawting o-on wevew {:?}", 🥺 *stawt);
}

system pawametews can be gwouped i-into tupwes (which c-can be nyested). OwO t-this is usefuw fow owganization.

fn compwex_system(
    (a, o.O mut b): (
        w-wes<wesouwcea>, (U ᵕ U❁)
        w-wesmut<wesouwceb>, (⑅˘꒳˘)
    ), ( ͡o ω ͡o )
    (q0, q-q1, UwU q2): (
        q-quewy<(/* … */)>, rawr x3
        q-quewy<(/* … */)>, rawr
        q-quewy<(/* … */)>, σωσ
    ),
) {
    // …
}

youw function can have a maximum o-of 16 totaw pawametews. OwO i-if you need m-mowe, gwoup them into tupwes to wowk awound t-the wimit. OwO t-tupwes can contain u-up to 16 membews, >_< but can be nyested indefinitewy.

thewe is awso a diffewent kind of s-system: excwusive systems. they have fuww diwect access to the ecs wowwd, XD so you can access any data you want and do anything, OwO b-but cannot wun i-in pawawwew. 🥺 fow m-most use cases, (ꈍᴗꈍ) you shouwd use weguwaw pawawwew s-systems.

fn wewoad_game(wowwd: &mut wowwd) {
    // ... a-access n-nyanievew we w-want fwom the w-wowwd
}

wuntime

in owdew fow youw systems to actuawwy b-be wun by bevy, OwO y-you nyeed to c-configuwe them via the app buiwdew:

fn main() {
    app::new()
        .add_pwugins(defauwtpwugins)
        // wun these o-onwy once at w-waunch
        .add_systems(stawtup, (U ᵕ U❁) (setup_camewa, (⑅˘꒳˘) d-debug_stawt))
        // w-wun t-these evewy fwame u-update
        .add_systems(update, ( ͡o ω ͡o ) (move_pwayew, UwU e-enemies_ai))
        // ...
        .wun();
}

be cawefuw: wwiting a nyew system fn and fowgetting to add it to youw a-app is a common mistake! OwO if you wun youw pwoject a-and youw n-nyew code doesn't s-seem to be wunning, (ꈍᴗꈍ) make suwe you added the s-system!

the above is enough fow simpwe pwojects.

systems awe contained in scheduwes. rawr x3 Update is the scheduwe whewe you typicawwy add any systems y-you want to wun e-evewy fwame. ^•ﻌ•^ Startup is whewe you typicawwy add systems that s-shouwd wun onwy o-once on app s-stawtup. OwO thewe awe awso othew possibiwities.

as youw pwoject gwows mowe compwex, OwO y-you might want t-to make use of s-some of the powewfuw toows that bevy offews fow m-managing when/how y-youw systems w-wun, OwO such as: expwicit owdewing, rawr x3 wun conditions, rawr x3 system sets, rawr x3 states.

one-shot systems

sometimes you don't want bevy to w-wun youw system f-fow you. OwO in that c-case, don't add it to a scheduwe.

if you awe a wwiting a system that y-you want to caww y-youwsewf whenevew you want (such as on a button pwess), ^•ﻌ•^ y-you can do t-that using one-shot systems.