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[ecs] Rework Entity to use u64 #2372

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ab95e01
[ecs] Rework 'Entity' to use 'u64'
NathanSWard Jun 16, 2021
2932210
use map directly with Entity::new
NathanSWard Jun 21, 2021
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122 changes: 56 additions & 66 deletions crates/bevy_ecs/src/entity/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,15 +21,18 @@ use std::{
/// Components of a specific entity can be accessed using
/// [`Query::get`](crate::system::Query::get) and related methods.
#[derive(Clone, Copy, Hash, Eq, Ord, PartialEq, PartialOrd)]
pub struct Entity {
pub(crate) generation: u32,
pub(crate) id: u32,
}
pub struct Entity(u64);
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We should have a non-doc comment here saying what scheme we use and why


impl Entity {
#[inline(always)]
fn from_id_and_gen(id: u32, gen: u32) -> Self {
Self(u64::from(gen) << 32 | u64::from(id))
}

/// Creates a new entity reference with a generation of 0.
#[inline(always)]
pub fn new(id: u32) -> Entity {
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Do we actually want this function?

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I've found this useful for writing tests before.

Entity { id, generation: 0 }
Self::from_id_and_gen(id, 0)
}

/// Convert to a form convenient for passing outside of rust.
Expand All @@ -38,42 +41,41 @@ impl Entity {
/// for serialization between runs.
///
/// No particular structure is guaranteed for the returned bits.
#[inline(always)]
pub fn to_bits(self) -> u64 {
u64::from(self.generation) << 32 | u64::from(self.id)
self.0
}

/// Reconstruct an `Entity` previously destructured with [`Entity::to_bits`].
///
/// Only useful when applied to results from `to_bits` in the same instance of an application.
#[inline(always)]
pub fn from_bits(bits: u64) -> Self {
Self {
generation: (bits >> 32) as u32,
id: bits as u32,
}
Self(bits)
}

/// Return a transiently unique identifier.
///
/// No two simultaneously-live entities share the same ID, but dead entities' IDs may collide
/// with both live and dead entities. Useful for compactly representing entities within a
/// specific snapshot of the world, such as when serializing.
#[inline]
#[inline(always)]
pub fn id(self) -> u32 {
self.id
self.0 as u32
}

/// Returns the generation of this Entity's id. The generation is incremented each time an
/// entity with a given id is despawned. This serves as a "count" of the number of times a
/// given id has been reused (id, generation) pairs uniquely identify a given Entity.
#[inline]
#[inline(always)]
pub fn generation(self) -> u32 {
self.generation
(self.0 >> 32) as u32
}
}

impl fmt::Debug for Entity {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}v{}", self.id, self.generation)
write!(f, "{}v{}", self.id(), self.generation())
}
}

Expand Down Expand Up @@ -106,11 +108,8 @@ impl<'a> Iterator for ReserveEntitiesIterator<'a> {
fn next(&mut self) -> Option<Self::Item> {
self.id_iter
.next()
.map(|&id| Entity {
generation: self.meta[id as usize].generation,
id,
})
.or_else(|| self.id_range.next().map(|id| Entity { generation: 0, id }))
.map(|&id| Entity::from_id_and_gen(id, self.meta[id as usize].generation))
.or_else(|| self.id_range.next().map(Entity::new))
}

fn size_hint(&self) -> (usize, Option<usize>) {
Expand Down Expand Up @@ -216,20 +215,14 @@ impl Entities {
if n > 0 {
// Allocate from the freelist.
let id = self.pending[(n - 1) as usize];
Entity {
generation: self.meta[id as usize].generation,
id,
}
Entity::from_id_and_gen(id, self.meta[id as usize].generation)
} else {
// Grab a new ID, outside the range of `meta.len()`. `flush()` must
// eventually be called to make it valid.
//
// As `self.free_cursor` goes more and more negative, we return IDs farther
// and farther beyond `meta.len()`.
Entity {
generation: 0,
id: u32::try_from(self.meta.len() as i64 - n).expect("too many entities"),
}
Entity::new(u32::try_from(self.meta.len() as i64 - n).expect("too many entities"))
}
}

Expand All @@ -251,14 +244,11 @@ impl Entities {
if let Some(id) = self.pending.pop() {
let new_free_cursor = self.pending.len() as i64;
*self.free_cursor.get_mut() = new_free_cursor;
Entity {
generation: self.meta[id as usize].generation,
id,
}
Entity::from_id_and_gen(id, self.meta[id as usize].generation)
} else {
let id = u32::try_from(self.meta.len()).expect("too many entities");
self.meta.push(EntityMeta::EMPTY);
Entity { generation: 0, id }
Entity::new(id)
}
}

Expand All @@ -269,27 +259,28 @@ impl Entities {
pub fn alloc_at(&mut self, entity: Entity) -> Option<EntityLocation> {
self.verify_flushed();

let loc = if entity.id as usize >= self.meta.len() {
self.pending.extend((self.meta.len() as u32)..entity.id);
let loc = if entity.id() as usize >= self.meta.len() {
self.pending.extend((self.meta.len() as u32)..entity.id());
let new_free_cursor = self.pending.len() as i64;
*self.free_cursor.get_mut() = new_free_cursor;
self.meta.resize(entity.id as usize + 1, EntityMeta::EMPTY);
self.meta
.resize(entity.id() as usize + 1, EntityMeta::EMPTY);
self.len += 1;
None
} else if let Some(index) = self.pending.iter().position(|item| *item == entity.id) {
} else if let Some(index) = self.pending.iter().position(|item| *item == entity.id()) {
self.pending.swap_remove(index);
let new_free_cursor = self.pending.len() as i64;
*self.free_cursor.get_mut() = new_free_cursor;
self.len += 1;
None
} else {
Some(mem::replace(
&mut self.meta[entity.id as usize].location,
&mut self.meta[entity.id() as usize].location,
EntityMeta::EMPTY.location,
))
};

self.meta[entity.id as usize].generation = entity.generation;
self.meta[entity.id() as usize].generation = entity.generation();

loc
}
Expand All @@ -300,15 +291,15 @@ impl Entities {
pub fn free(&mut self, entity: Entity) -> Option<EntityLocation> {
self.verify_flushed();

let meta = &mut self.meta[entity.id as usize];
if meta.generation != entity.generation {
let meta = &mut self.meta[entity.id() as usize];
if meta.generation != entity.generation() {
return None;
}
meta.generation += 1;

let loc = mem::replace(&mut meta.location, EntityMeta::EMPTY.location);

self.pending.push(entity.id);
self.pending.push(entity.id());

let new_free_cursor = self.pending.len() as i64;
*self.free_cursor.get_mut() = new_free_cursor;
Expand All @@ -331,8 +322,8 @@ impl Entities {
// Note that out-of-range IDs are considered to be "contained" because
// they must be reserved IDs that we haven't flushed yet.
self.meta
.get(entity.id as usize)
.map_or(true, |meta| meta.generation == entity.generation)
.get(entity.id() as usize)
.map_or(true, |meta| meta.generation == entity.generation())
}

pub fn clear(&mut self) {
Expand All @@ -345,8 +336,8 @@ impl Entities {
///
/// Must not be called on pending entities.
pub fn get_mut(&mut self, entity: Entity) -> Option<&mut EntityLocation> {
let meta = &mut self.meta[entity.id as usize];
if meta.generation == entity.generation {
let meta = &mut self.meta[entity.id() as usize];
if meta.generation == entity.generation() {
Some(&mut meta.location)
} else {
None
Expand All @@ -355,9 +346,9 @@ impl Entities {

/// Returns `Ok(Location { archetype: 0, index: undefined })` for pending entities.
pub fn get(&self, entity: Entity) -> Option<EntityLocation> {
if (entity.id as usize) < self.meta.len() {
let meta = &self.meta[entity.id as usize];
if meta.generation != entity.generation {
if (entity.id() as usize) < self.meta.len() {
let meta = &self.meta[entity.id() as usize];
if meta.generation != entity.generation() {
return None;
}
Some(meta.location)
Expand All @@ -376,18 +367,15 @@ impl Entities {

if meta_len > id as usize {
let meta = &self.meta[id as usize];
Entity {
generation: meta.generation,
id,
}
Entity::from_id_and_gen(id, meta.generation)
} else {
// See if it's pending, but not yet flushed.
let free_cursor = self.free_cursor.load(Ordering::Relaxed);
let num_pending = std::cmp::max(-free_cursor, 0) as usize;

if meta_len + num_pending > id as usize {
// Pending entities will have generation 0.
Entity { generation: 0, id }
Entity::new(id)
} else {
panic!("entity id is out of range");
}
Expand All @@ -413,10 +401,7 @@ impl Entities {
self.len += -current_free_cursor as u32;
for (id, meta) in self.meta.iter_mut().enumerate().skip(old_meta_len) {
init(
Entity {
id: id as u32,
generation: meta.generation,
},
Entity::from_id_and_gen(id as u32, meta.generation),
&mut meta.location,
);
}
Expand All @@ -429,10 +414,7 @@ impl Entities {
for id in self.pending.drain(new_free_cursor..) {
let meta = &mut self.meta[id as usize];
init(
Entity {
id,
generation: meta.generation,
},
Entity::from_id_and_gen(id, meta.generation),
&mut meta.location,
);
}
Expand Down Expand Up @@ -481,10 +463,7 @@ mod tests {

#[test]
fn entity_bits_roundtrip() {
let e = Entity {
generation: 0xDEADBEEF,
id: 0xBAADF00D,
};
let e = Entity::from_id_and_gen(0xBAADF00D, 0xDEADBEEF);
assert_eq!(Entity::from_bits(e.to_bits()), e);
}

Expand All @@ -495,4 +474,15 @@ mod tests {
e.flush(|_, _| {});
assert_eq!(e.len(), 1);
}

#[test]
fn test_entity() {
let e = Entity::from_id_and_gen(33, 42);
assert_eq!(e.id(), 33);
assert_eq!(e.generation(), 42);

let e = Entity::new(33);
assert_eq!(e.id(), 33);
assert_eq!(e.generation(), 0);
}
}
14 changes: 7 additions & 7 deletions crates/bevy_ecs/src/world/entity_ref.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,7 @@ impl<'w> EntityMut<'w> {
let old_archetype = &mut archetypes[current_location.archetype_id];
let result = old_archetype.swap_remove(current_location.index);
if let Some(swapped_entity) = result.swapped_entity {
entities.meta[swapped_entity.id as usize].location = current_location;
entities.meta[swapped_entity.id() as usize].location = current_location;
}
(result.table_row, old_archetype.table_id())
};
Expand Down Expand Up @@ -246,7 +246,7 @@ impl<'w> EntityMut<'w> {
new_location
};

entities.meta[entity.id as usize].location = new_location;
entities.meta[entity.id() as usize].location = new_location;
let (old_archetype, new_archetype) =
archetypes.get_2_mut(current_location.archetype_id, new_archetype_id);
let edge = old_archetype
Expand Down Expand Up @@ -342,7 +342,7 @@ impl<'w> EntityMut<'w> {

let remove_result = old_archetype.swap_remove(old_location.index);
if let Some(swapped_entity) = remove_result.swapped_entity {
entities.meta[swapped_entity.id as usize].location = old_location;
entities.meta[swapped_entity.id() as usize].location = old_location;
}
let old_table_row = remove_result.table_row;
let old_table_id = old_archetype.table_id();
Expand Down Expand Up @@ -374,7 +374,7 @@ impl<'w> EntityMut<'w> {
};

self.location = new_location;
entities.meta[self.entity.id as usize].location = new_location;
entities.meta[self.entity.id() as usize].location = new_location;

Some(result)
}
Expand Down Expand Up @@ -427,7 +427,7 @@ impl<'w> EntityMut<'w> {

let remove_result = old_archetype.swap_remove(old_location.index);
if let Some(swapped_entity) = remove_result.swapped_entity {
entities.meta[swapped_entity.id as usize].location = old_location;
entities.meta[swapped_entity.id() as usize].location = old_location;
}
let old_table_row = remove_result.table_row;
let old_table_id = old_archetype.table_id();
Expand Down Expand Up @@ -458,7 +458,7 @@ impl<'w> EntityMut<'w> {
};

self.location = new_location;
entities.meta[self.entity.id as usize].location = new_location;
entities.meta[self.entity.id() as usize].location = new_location;
}

pub fn insert<T: Component>(&mut self, value: T) -> &mut Self {
Expand Down Expand Up @@ -488,7 +488,7 @@ impl<'w> EntityMut<'w> {
}
let remove_result = archetype.swap_remove(location.index);
if let Some(swapped_entity) = remove_result.swapped_entity {
world.entities.meta[swapped_entity.id as usize].location = location;
world.entities.meta[swapped_entity.id() as usize].location = location;
}
table_row = remove_result.table_row;

Expand Down
2 changes: 1 addition & 1 deletion crates/bevy_ecs/src/world/spawn_batch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -105,7 +105,7 @@ where
bundle,
self.change_tick,
);
self.entities.meta[entity.id as usize].location = location;
self.entities.meta[entity.id() as usize].location = location;
}
Some(entity)
}
Expand Down