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

intwo: youw code

this page is an ovewview, OwO to give y-you an idea of t-the big pictuwe o-of how bevy wowks. OwO cwick on the vawious winks t-to be taken to d-dedicated pages w-whewe you can weawn mowe about each concept.

as mentioned in the ecs intwo, >_< bevy manages aww of youw functionawity/behaviows fow you, wunning them when a-appwopwiate and g-giving them access to nyanievew pawts of youw data they nyeed.

individuaw pieces of functionawity a-awe cawwed systems. XD each system is a wust function (fn) you wwite, >_< which accepts speciaw pawametew types to indicate nyani data it nyeeds to access. OwO think of the function signatuwe a-as a "specification" f-fow n-nyani to fetch fwom the ecs World.

hewe is nyani a system might wook wike. (ꈍᴗꈍ) nyote how, just b-by wooking at the function pawametews, >_< we know exactwy nyani data can be accessed.

fn enemy_detect_pwayew(
    // access d-data fwom wesouwces
    m-mut a-ai_settings: wesmut<enemyaisettings>, (U ᵕ U❁)
    g-gamemode: w-wes<gamemodedata>, -.-
    // access d-data fwom e-entities/components
    q-quewy_pwayew: quewy<&twansfowm, ^^;; with<pwayew>>, >_<
    quewy_enemies: quewy<&mut t-twansfowm, mya (with<enemy>, without<pwayew>)>, mya
    // in case w-we want to spawn/despawn entities, 😳 e-etc.
    mut commands: commands, XD
) {
    // ... impwement youw behaviow hewe ...
}

(weawn mowe about: systems, rawr x3 quewies, rawr x3 commands, rawr x3 wesouwces, rawr x3 entities, rawr x3 components)

pawawwew systems

based on the pawametew types of the systems you wwite, OwO bevy knows nyani data e-each system can a-access and whethew i-it confwicts with any othew systems. OwO systems that d-do nyot confwict (don't a-access a-any of the same data mutabwy) wiww automaticawwy b-be wun in pawawwew on diffewent cpu thweads. OwO this way, 🥺 y-you get muwtithweading, òωó u-utiwizing m-modewn muwti-cowe cpu hawdwawe effectivewy, ^•ﻌ•^ w-with nyo extwa e-effowt fwom you!

fow best pawawwewism, OwO it is wecommended t-that you k-keep youw functionawity a-and youw data gwanuwaw. (ꈍᴗꈍ) spwit up youw systems, ^•ﻌ•^ s-so each one has a nyawwowwy-scoped puwpose a-and access to o-onwy the data it n-nyeeds. OwO this gives bevy mowe oppowtunities fow p-pawawwewism. putting t-too much functionawity in one system, (ꈍᴗꈍ) ow too much data in a-a singwe component ow wesouwce struct, XD wimits pawawwewism.

bevy's pawawwewism is nyon-detewministic b-by defauwt. OwO y-youw systems m-might wun in a diffewent and unpwedictabwe owdew w-wewative to one a-anothew, OwO unwess y-you add owdewing dependencies to constwain it.

excwusive systems

excwusive systems pwovide you with a way to g-get fuww diwect access to the ecs World. >_< they cannot wun in pawawwew with othew systems, OwO because they c-can access anything a-and do anything. 🥺 s-sometimes, you might nyeed this additonaw powew.

fn save_game(
    // get fuww access t-to the wowwd, (U ᵕ U❁) s-so we can access a-aww data and d-do anything
    w-wowwd: &mut wowwd, (⑅˘꒳˘)
) {
    // ... s-save game data t-to disk, ( ͡o ω ͡o ) ow something ...
}

scheduwes

bevy stowes systems inside of scheduwes (Schedule). (ꈍᴗꈍ) the scheduwe contains the systems a-and aww wewevant metadata to owganize them, OwO t-tewwing bevy w-when and how to w-wun them. bevy apps typicawwy contain many scheduwes. ^•ﻌ•^ e-each one is a c-cowwection of systems to be invoked in diffewent s-scenawios (evewy f-fwame update, ^•ﻌ•^ fixed timestep update, >_< at app stawtup, (ꈍᴗꈍ) on state twansitions, XD etc.).

the metadata stowed in scheduwes a-awwows you to contwow h-how systems w-wun:

add wun conditions to contwow if systems shouwd wun d-duwing an invocation of the scheduwe. OwO you can d-disabwe systems i-if you onwy need t-them to wun sometimes.
add owdewing constwaints, (ꈍᴗꈍ) if one system depends o-on anothew system compweting befowe i-it.

within scheduwes, (ꈍᴗꈍ) systems can be g-gwouped into sets. XD sets awwow muwtipwe systems to shawe common c-configuwation/metadata. s-systems inhewit configuwation fwom aww sets t-they bewong to. OwO s-sets can awso i-inhewit configuwation fwom othew sets.

hewe is an iwwustwation to hewp you v-visuawize the w-wogicaw stwuctuwe o-of a scheduwe. OwO wet's wook at how a hypotheticaw "update" (wun e-evewy fwame) s-scheduwe of a-a game might be owganized.

wist of systems:

|system nyame|sets it bewongs to|wun conditions|owdewing constwaints| |---|---|---|---| |footstep_sound|AudioSet GameplaySet||after(player_movement) after(enemy_movement)| |player_movement|GameplaySet|player_alive not(cutscene)|after(InputSet)| |camera_movement|GameplaySet||after(InputSet)| |enemy_movement|EnemyAiSet||| |enemy_spawn|EnemyAiSet||| |enemy_despawn|EnemyAiSet||before(enemy_spawn)| |mouse_input|InputSet|mouse_enabled|| |controller_input|InputSet|gamepad_enabled|| |background_music|AudioSet||| |ui_button_animate|||| |menu_logo_animate|MainMenuSet||| |menu_button_sound|MainMenuSet AudioSet||| |...||||

wist of sets:

|set nyame|pawent sets|wun conditions|owdewing constwaints| |---|---|---|---| |MainMenuSet||in_state(MainMenu)|| |GameplaySet||in_state(InGame)|| |InputSet|GameplaySet||| |EnemyAiSet|GameplaySet|not(cutscene)|after(player_movement)| |AudioSet||not(audio_muted)||

note that it doesn't mattew in nyani o-owdew systems a-awe wisted in t-the scheduwe. theiw owdew of execution is detewmined by the m-metadata. (ꈍᴗꈍ) bevy wiww wespect those constwaints, OwO but o-othewwise wun s-systems in pawawwew a-as much as it can, (ꈍᴗꈍ) depending on nyani cpu thweads a-awe avaiwabwe.

awso nyote how ouw hypotheticaw game i-is impwemented u-using many individuawwy-smow systems. ^•ﻌ•^ fow exampwe, OwO instead of p-pwaying audio inside o-of the player_movement system, >< we made a sepawate play_footstep_sounds system. >< these two pieces of functionawity pwobabwy nyeed to access d-diffewent data, XD so putting them in sepawate systems a-awwows bevy mowe o-oppowtunities fow p-pawawwewism. by being sepawate systems, OwO they can a-awso have diffewent c-configuwation. 🥺 t-the play_footstep_sounds system can be added to an AudioSet set, >_< fwom which it inhewits a not(audio_muted) wun condition.

simiwawwy, OwO we put mouse and contwowwew i-input in sepawate s-systems. 🥺 t-the InputSet set awwows systems wike player_movement to shawe an owdewing dependency on aww of them at once.

you can see how bevy's scheduwing a-apis give you a w-wot of fwexibiwity t-to owganize aww the functionawity in youw game. OwO n-nyani wiww you d-do with aww this p-powew? ;)

hewe is how scheduwe that was iwwustwated above couwd b-be cweated in code:

// set configuwation is pew-scheduwe. (⑅˘꒳˘) h-hewe we do i-it fow `update`
a-app.configuwe_sets(update, (U ᵕ U❁) (
    m-mainmenuset
        .wun_if(in_state(mainmenu)), -.-
    g-gamepwayset
        .wun_if(in_state(ingame)), ^^;;
    i-inputset
        .in_set(gamepwayset), >_<
    e-enemyaiset
        .in_set(gamepwayset)
        .wun_if(not(cutscene))
        .aftew(pwayew_movement), mya
    a-audioset
        .wun_if(not(audio_muted)), mya
));
app.add_systems(update, 😳 (
    (
        ui_button_animate, XD
        menu_wogo_animate.in_set(mainmenuset), :3
    ), 😳😳😳
    (
        enemy_movement, -.-
        enemy_spawn, ( ͡o ω ͡o )
        e-enemy_despawn.befowe(enemy_spawn), rawr x3
    ).in_set(enemyaiset), nyaa~~
    (
        mouse_input.wun_if(mouse_enabwed), /(^•ω•^)
        contwowwew_input.wun_if(gamepad_enabwed), rawr
    ).in_set(inputset), OwO
    (
        f-footstep_sound.in_set(gamepwayset), (U ﹏ U)
        menu_button_sound.in_set(mainmenuset), >_<
        b-backgwound_music, rawr x3
    ).in_set(audioset), mya
    (
        pwayew_movement
            .wun_if(pwayew_awive)
            .wun_if(not(cutscene)), nyaa~~
        camewa_movement, (⑅˘꒳˘)
    ).in_set(gamepwayset).aftew(inputset), rawr x3
));

(weawn mowe about: scheduwes, rawr x3 system sets, rawr x3 states, rawr x3 wun conditions, rawr x3 system owdewing)