pub trait Marker: Clone + Component + Debug + Eq + Hash + DeserializeOwned + Serialize {
type Identifier;
type Allocator: MarkerAllocator<Self>;
fn id(&self) -> Self::Identifier;
fn update(&mut self, new_revision: Self) { ... }
}
Expand description
This trait should be implemented by a component which is going to be used as marker.
This marker should be set to entity that should be serialized.
If serialization strategy needs to set marker to some entity
then it should use newly allocated marker from Marker::Allocator
.
Example
extern crate specs;
#[macro_use] extern crate serde;
use std::collections::HashMap;
use std::ops::Range;
use specs::prelude::*;
use specs::world::EntitiesRes;
use specs::saveload::{MarkedBuilder, Marker, MarkerAllocator};
// Marker for entities that should be synced over network
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]
struct NetMarker {
id: u64,
seq: u64,
}
impl Component for NetMarker {
type Storage = DenseVecStorage<Self>;
}
impl Marker for NetMarker {
type Identifier = u64;
type Allocator = NetNode;
fn id(&self) -> u64 {
self.id
}
// Updates sequence id.
// Entities with too old sequence id get deleted.
fn update(&mut self, update: Self) {
assert_eq!(self.id, update.id);
self.seq = update.seq;
}
}
// Each client and server has one
// Contains id range and `NetMarker -> Entity` mapping
struct NetNode {
range: Range<u64>,
mapping: HashMap<u64, Entity>,
}
impl MarkerAllocator<NetMarker> for NetNode {
fn allocate(&mut self, entity: Entity, id: Option<u64>) -> NetMarker {
let id = id.unwrap_or_else(|| {
self.range.next().expect("Id range must be virtually endless")
});
let marker = NetMarker {
id: id,
seq: 0,
};
self.mapping.insert(id, entity);
marker
}
fn retrieve_entity_internal(&self, id: u64) -> Option<Entity> {
self.mapping.get(&id).cloned()
}
fn maintain(&mut self, entities: &EntitiesRes, storage: &ReadStorage<NetMarker>) {
self.mapping = (entities, storage)
.join()
.map(|(e, m)| (m.id(), e))
.collect();
}
}
fn main() {
let mut world = World::new();
world.register::<NetMarker>();
world.add_resource(
NetNode {
range: 0..100,
mapping: HashMap::new(),
}
);
let entity = world.create_entity().marked::<NetMarker>().build();
let storage = &mut world.write_storage::<NetMarker>();
let marker = storage.get(entity).unwrap().clone();
assert_eq!(
world.write_resource::<NetNode>().retrieve_entity(marker, storage, &world.entities()),
entity
);
}
Required Associated Types
sourcetype Identifier
type Identifier
Id of the marker
sourcetype Allocator: MarkerAllocator<Self>
type Allocator: MarkerAllocator<Self>
Allocator for this Marker
Required Methods
sourcefn id(&self) -> Self::Identifier
fn id(&self) -> Self::Identifier
Get this marker internal id. The value of this method should be constant.
Provided Methods
sourcefn update(&mut self, new_revision: Self)
fn update(&mut self, new_revision: Self)
This gets called when an entity is deserialized by DeserializeComponents
.
It can be used to update internal data that is not used for
identification.
Contract
This function may assume that self.id() == new_revision.id()
.
However, it must not exhibit undefined behavior in such a case.
Panics
May panic if self.id()
!= new_revision.id()
.
Default implementation
The default implementation just sets self
to new_revision
.
Examples
#[derive(Clone, Debug, Deserialize, Eq, Hash, Serialize)]
struct MyMarker {
id: u64,
last_modified: String,
}
impl Marker for MyMarker {
type Identifier = u64;
fn id(&self) -> u64 {
self.id
}
fn update(&self, new: Self) {
self.last_modified = new.last_modified;
}
}
Now, the marker always contains the name of the client who updated the entity associated with this marker.