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//! Definitions for [`Resource`] reflection.
//!
//! # Architecture
//!
//! See the module doc for [`crate::reflect::component`].
use crate::{
change_detection::Mut,
system::Resource,
world::{unsafe_world_cell::UnsafeWorldCell, World},
};
use bevy_reflect::{FromReflect, FromType, Reflect, TypeRegistry};
use super::from_reflect_with_fallback;
/// A struct used to operate on reflected [`Resource`] of a type.
///
/// A [`ReflectResource`] for type `T` can be obtained via
/// [`bevy_reflect::TypeRegistration::data`].
#[derive(Clone)]
pub struct ReflectResource(ReflectResourceFns);
/// The raw function pointers needed to make up a [`ReflectResource`].
///
/// This is used when creating custom implementations of [`ReflectResource`] with
/// [`ReflectResource::new()`].
///
/// > **Note:**
/// > Creating custom implementations of [`ReflectResource`] is an advanced feature that most users
/// > will not need.
/// > Usually a [`ReflectResource`] is created for a type by deriving [`Reflect`]
/// > and adding the `#[reflect(Resource)]` attribute.
/// > After adding the component to the [`TypeRegistry`],
/// > its [`ReflectResource`] can then be retrieved when needed.
///
/// Creating a custom [`ReflectResource`] may be useful if you need to create new resource types at
/// runtime, for example, for scripting implementations.
///
/// By creating a custom [`ReflectResource`] and inserting it into a type's
/// [`TypeRegistration`][bevy_reflect::TypeRegistration],
/// you can modify the way that reflected resources of that type will be inserted into the bevy
/// world.
#[derive(Clone)]
pub struct ReflectResourceFns {
/// Function pointer implementing [`ReflectResource::insert()`].
pub insert: fn(&mut World, &dyn Reflect, &TypeRegistry),
/// Function pointer implementing [`ReflectResource::apply()`].
pub apply: fn(&mut World, &dyn Reflect),
/// Function pointer implementing [`ReflectResource::apply_or_insert()`].
pub apply_or_insert: fn(&mut World, &dyn Reflect, &TypeRegistry),
/// Function pointer implementing [`ReflectResource::remove()`].
pub remove: fn(&mut World),
/// Function pointer implementing [`ReflectResource::reflect()`].
pub reflect: fn(&World) -> Option<&dyn Reflect>,
/// Function pointer implementing [`ReflectResource::reflect_unchecked_mut()`].
///
/// # Safety
/// The function may only be called with an [`UnsafeWorldCell`] that can be used to mutably access the relevant resource.
pub reflect_unchecked_mut: unsafe fn(UnsafeWorldCell<'_>) -> Option<Mut<'_, dyn Reflect>>,
/// Function pointer implementing [`ReflectResource::copy()`].
pub copy: fn(&World, &mut World, &TypeRegistry),
}
impl ReflectResourceFns {
/// Get the default set of [`ReflectResourceFns`] for a specific resource type using its
/// [`FromType`] implementation.
///
/// This is useful if you want to start with the default implementation before overriding some
/// of the functions to create a custom implementation.
pub fn new<T: Resource + FromReflect>() -> Self {
<ReflectResource as FromType<T>>::from_type().0
}
}
impl ReflectResource {
/// Insert a reflected [`Resource`] into the world like [`insert()`](World::insert_resource).
pub fn insert(&self, world: &mut World, resource: &dyn Reflect, registry: &TypeRegistry) {
(self.0.insert)(world, resource, registry);
}
/// Uses reflection to set the value of this [`Resource`] type in the world to the given value.
///
/// # Panics
///
/// Panics if there is no [`Resource`] of the given type.
pub fn apply(&self, world: &mut World, resource: &dyn Reflect) {
(self.0.apply)(world, resource);
}
/// Uses reflection to set the value of this [`Resource`] type in the world to the given value or insert a new one if it does not exist.
pub fn apply_or_insert(
&self,
world: &mut World,
resource: &dyn Reflect,
registry: &TypeRegistry,
) {
(self.0.apply_or_insert)(world, resource, registry);
}
/// Removes this [`Resource`] type from the world. Does nothing if it doesn't exist.
pub fn remove(&self, world: &mut World) {
(self.0.remove)(world);
}
/// Gets the value of this [`Resource`] type from the world as a reflected reference.
pub fn reflect<'a>(&self, world: &'a World) -> Option<&'a dyn Reflect> {
(self.0.reflect)(world)
}
/// Gets the value of this [`Resource`] type from the world as a mutable reflected reference.
pub fn reflect_mut<'a>(&self, world: &'a mut World) -> Option<Mut<'a, dyn Reflect>> {
// SAFETY: unique world access
unsafe { (self.0.reflect_unchecked_mut)(world.as_unsafe_world_cell()) }
}
/// # Safety
/// This method does not prevent you from having two mutable pointers to the same data,
/// violating Rust's aliasing rules. To avoid this:
/// * Only call this method with an [`UnsafeWorldCell`] which can be used to mutably access the resource.
/// * Don't call this method more than once in the same scope for a given [`Resource`].
pub unsafe fn reflect_unchecked_mut<'w>(
&self,
world: UnsafeWorldCell<'w>,
) -> Option<Mut<'w, dyn Reflect>> {
// SAFETY: caller promises to uphold uniqueness guarantees
unsafe { (self.0.reflect_unchecked_mut)(world) }
}
/// Gets the value of this [`Resource`] type from `source_world` and [applies](Self::apply()) it to the value of this [`Resource`] type in `destination_world`.
///
/// # Panics
///
/// Panics if there is no [`Resource`] of the given type.
pub fn copy(
&self,
source_world: &World,
destination_world: &mut World,
registry: &TypeRegistry,
) {
(self.0.copy)(source_world, destination_world, registry);
}
/// Create a custom implementation of [`ReflectResource`].
///
/// This is an advanced feature,
/// useful for scripting implementations,
/// that should not be used by most users
/// unless you know what you are doing.
///
/// Usually you should derive [`Reflect`] and add the `#[reflect(Resource)]` component
/// to generate a [`ReflectResource`] implementation automatically.
///
/// See [`ReflectResourceFns`] for more information.
pub fn new(&self, fns: ReflectResourceFns) -> Self {
Self(fns)
}
/// The underlying function pointers implementing methods on `ReflectResource`.
///
/// This is useful when you want to keep track locally of an individual
/// function pointer.
///
/// Calling [`TypeRegistry::get`] followed by
/// [`TypeRegistration::data::<ReflectResource>`] can be costly if done several
/// times per frame. Consider cloning [`ReflectResource`] and keeping it
/// between frames, cloning a `ReflectResource` is very cheap.
///
/// If you only need a subset of the methods on `ReflectResource`,
/// use `fn_pointers` to get the underlying [`ReflectResourceFns`]
/// and copy the subset of function pointers you care about.
///
/// [`TypeRegistration::data::<ReflectResource>`]: bevy_reflect::TypeRegistration::data
/// [`TypeRegistry::get`]: bevy_reflect::TypeRegistry::get
pub fn fn_pointers(&self) -> &ReflectResourceFns {
&self.0
}
}
impl<R: Resource + FromReflect> FromType<R> for ReflectResource {
fn from_type() -> Self {
ReflectResource(ReflectResourceFns {
insert: |world, reflected_resource, registry| {
let resource = from_reflect_with_fallback::<R>(reflected_resource, world, registry);
world.insert_resource(resource);
},
apply: |world, reflected_resource| {
let mut resource = world.resource_mut::<R>();
resource.apply(reflected_resource);
},
apply_or_insert: |world, reflected_resource, registry| {
if let Some(mut resource) = world.get_resource_mut::<R>() {
resource.apply(reflected_resource);
} else {
let resource =
from_reflect_with_fallback::<R>(reflected_resource, world, registry);
world.insert_resource(resource);
}
},
remove: |world| {
world.remove_resource::<R>();
},
reflect: |world| world.get_resource::<R>().map(|res| res as &dyn Reflect),
reflect_unchecked_mut: |world| {
// SAFETY: all usages of `reflect_unchecked_mut` guarantee that there is either a single mutable
// reference or multiple immutable ones alive at any given point
unsafe {
world.get_resource_mut::<R>().map(|res| Mut {
value: res.value as &mut dyn Reflect,
ticks: res.ticks,
})
}
},
copy: |source_world, destination_world, registry| {
let source_resource = source_world.resource::<R>();
let destination_resource =
from_reflect_with_fallback::<R>(source_resource, destination_world, registry);
destination_world.insert_resource(destination_resource);
},
})
}
}