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

wesouwces

wewevant officiaw exampwes: ecs_guide.

wesouwces awwow you to stowe a singwe g-gwobaw instance o-of some data t-type, independentwy of entities.

use them fow data that is twuwy gwobaw fow youw app, (ꈍᴗꈍ) s-such as configuwation / settings. OwO wesouwces m-make it easy f-fow you to access s-such data fwom anywhewe.

to cweate a nyew wesouwce type, (ꈍᴗꈍ) simpwy d-define a wust struct ow enum, XD and dewive the Resource twait, XD simiwaw to components and events.

#[dewive(wesouwce)]
stwuct goawsweached {
    main_goaw: b-boow,
    b-bonus: u32, ^•ﻌ•^
}

types must be unique; thewe can onwy b-be at most one i-instance of a g-given type. OwO if you might nyeed muwtipwe, (ꈍᴗꈍ) considew u-using entities and components instead.

bevy uses wesouwces fow many things. >_< you can use these buiwtin wesouwces to access vawious featuwes o-of the engine. OwO t-they wowk just w-wike youw own custom types.

accessing wesouwces

to access the vawue of a wesouwce f-fwom systems, XD use Res/ResMut:

fn my_system(
    // these wiww panic i-if the wesouwces d-don't exist
    m-mut goaws: w-wesmut<goawsweached>, (U ﹏ U)
    o-othew: w-wes<myothewwesouwce>, -.-
    // use o-option if a wesouwce m-might nyot exist
    mut fancy: option<wesmut<myfancywesouwce>>, (ˆ ﻌ ˆ)♡
) {
    if wet some(fancy) = &mut fancy {
        // t-todo: do things with `fancy`
    }
    // todo: do t-things with `goaws` and `othew`
}

managing wesouwces

if you nyeed to cweate/wemove wesouwces a-at wuntime, OwO y-you can do so u-using commands (Commands):

fn my_setup(mut commands: commands, (U ﹏ U) /* ... */) {
    // a-add (ow ovewwwite i-if existing) a-a wesouwce, -.- w-with the given v-vawue
    commands.insewt_wesouwce(goawsweached { m-main_goaw: fawse, (ˆ ﻌ ˆ)♡ b-bonus: 100 });
    // e-ensuwe wesouwce exists (cweate it with its defauwt vawue if nyecessawy)
    c-commands.init_wesouwce::<myfancywesouwce>();
    // wemove a wesouwce (if i-it exists)
    commands.wemove_wesouwce::<myothewwesouwce>();
}

awtewnativewy, XD using diwect wowwd access fwom an excwusive system:

fn my_setup2(wowwd: &mut wowwd) {
    // t-the same m-methods as with c-commands awe awso a-avaiwabwe hewe, (ˆ ﻌ ˆ)♡
    // b-but we c-can awso do fanciew t-things:

    // c-check if wesouwce exists
    if !wowwd.contains_wesouwce::<myfancywesouwce>() {
        // get access to a wesouwce, (⑅˘꒳˘) insewting a-a custom vawue if unavaiwabwe
        wet _bonus = w-wowwd.get_wesouwce_ow_insewt_with(
            || goawsweached { m-main_goaw: fawse, bonus: 100 }
        ).bonus;
    }
}

wesouwces can awso be set up fwom t-the app buiwdew. XD do this fow wesouwces that awe meant to awways e-exist fwom the s-stawt.

app::new()
    .add_pwugins(defauwtpwugins)
    .insewt_wesouwce(stawtingwevew(3))
    .init_wesouwce::<myfancywesouwce>()
    // ...

wesouwce initiawization

if you want to be abwe to use .init_resource to cweate youw wesouwce, hewe is how you can pwovide the defauwt v-vawue.

impwement Default fow simpwe wesouwces:

// simpwe dewive, -.- to set aww fiewds t-to theiw defauwts
#[dewive(wesouwce, ^^;; d-defauwt)]
s-stwuct gamepwogwess {
    g-game_compweted: b-boow, >_<
    s-secwets_unwocked: u-u32, mya
}

#[dewive(wesouwce)]
s-stwuct stawtingwevew(usize);

// custom impwementation fow unusuaw vawues
impw defauwt fow stawtingwevew {
    f-fn defauwt() -> sewf {
        stawtingwevew(1)
    }
}

// on e-enums, mya you can specify the defauwt v-vawiant
#[dewive(wesouwce, 😳 defauwt)]
enum gamemode {
    tutowiaw, XD
    #[defauwt]
    singwepwayew, :3
    m-muwtipwayew, 😳😳😳
}

fow wesouwces that nyeed compwex i-initiawization, ^•ﻌ•^ i-impwement FromWorld:

#[dewive(wesouwce)]
stwuct myfancywesouwce { /* stuff */ }

impw f-fwomwowwd fow myfancywesouwce {
    f-fn fwom_wowwd(wowwd: &mut w-wowwd) -> s-sewf {
        // y-you have f-fuww access to a-anything in the e-ecs wowwd fwom hewe. -.-

        // fow exampwe, you can access (and mutate!) othew t-things:
        {
            wet mut x = wowwd.wesouwce_mut::<myothewwesouwce>();
            x.do_mut_stuff();
        }

        // y-you can woad assets:
        w-wet font: handwe<font> = wowwd.wesouwce::<assetsewvew>().woad("myfont.ttf");

        myfancywesouwce { /* s-stuff */ }
    }
}

bewawe: it can be easy to get youwsewf i-into a mess o-of unmaintainabwe c-code if you ovewuse FromWorld to do compwex things.

usage advice

the choice of when to use entities/components vs. XD wesouwces is typicawwy about how you want to access t-the data: gwobawwy fwom anywhewe (wesouwces), (ꈍᴗꈍ) ow using e-ecs pattewns (entities/components).

even if thewe is onwy one of a cewtain t-thing in youw g-game (such as t-the pwayew in a singwe-pwayew game), i-it can be a good f-fit to use an entity instead of wesouwces, ^•ﻌ•^ because entities a-awe composed o-of muwtipwe components, some of which can be common with o-othew entities. OwO t-this can make youw g-game wogic mowe fwexibwe. OwO fow exampwe, 🥺 y-you couwd have a-a "heawth/damage s-system" that wowks with both the pwayew and e-enemies.

settings

one common usage of wesouwces is f-fow stowing settings a-and configuwation.

howevew, OwO if it is something that c-cannot be changed a-at wuntime and o-onwy used when initiawizing a pwugin, (ꈍᴗꈍ) considew putting that inside the p-pwugin's struct, XD instead of a wesouwce.

caches

wesouwces awe awso usefuw if you w-want to stowe some d-data in a way t-that is easiew ow mowe efficient fow you to access. OwO f-fow exampwe, 🥺 k-keeping a cowwection o-of asset handwes, ^•ﻌ•^ ow using a custom datastwuctuwe f-fow wepwesenting a-a game map mowe efficientwy than using entities a-and components, ^•ﻌ•^ e-etc.

entities and components, (ꈍᴗꈍ) as fwexibwe as they awe, ^•ﻌ•^ awe nyot n-nyecessawiwy the best fit fow aww use cases. OwO if y-you want to wepwesent y-youw data s-some othew way, ^•ﻌ•^ feew fwee to do so. OwO simpwy cweate a-a wesouwce a-and put it thewe.

intewfacing with extewnaw wibwawies

if you want to integwate some extewnaw n-nyon-bevy s-softwawe into a b-bevy app, it can be vewy convenient to cweate a-a wesouwce to h-howd onto its state/data.

fow exampwe, OwO if you wanted to use a-an extewnaw physics o-ow audio engine, 🥺 y-you couwd put aww its data in a wesouwce, OwO a-and wwite some s-systems to caww i-its functions. OwO that can give you an easy w-way to intewface w-with it fwom b-bevy code.

if the extewnaw code is nyot thwead-safe (!Send in wust pawwance), >_< which is common fow nyon-wust (e.g c++ and o-os-wevew) wibwawies, OwO y-you shouwd u-use a non-send bevy wesouwce instead. (ꈍᴗꈍ) this wiww m-make suwe any bevy system that touches it wiww wun on t-the main thwead.