Crate constellation [−] [src]
Constellation ECS
A data-oriented entity component system optimized for cache coherent resource access and parallel system execution.
Constellation does not have any native understanding of a "component". Instead, the library is concerned about ensuring safe concurrent access to shared resources, while providing direct access to each resource's own APIs. These resources may store per-entity data such as positions, or may represent application wide services such as asset loaders or input devices.
Systems request read or write access to a set of resources, which can then be scheduled to
be potentially executed in parallel by recording them into a SystemCommandBuffer
and
executing the command buffer within a World
.
Examples
Defining Resources:
// Per-entity position data. struct Position { x: f32, y: f32, z: f32 } // Store position data into a vector resource type Positions = VecResource<Position>; // Per-entity debug names. struct DebugName { name: String } // Store debug names in a map resource type DebugNames = MapResource<DebugName>; let mut world = World::new(); world.register_resource(Positions::new()); world.register_resource(DebugNames::new());
Update the world with Systems:
let mut update = SystemCommandBuffer::default(); update.queue_systems(|scope| { scope.run_r1w1(|ctx, velocities: &Velocities, positions: &mut Positions| { println!("Updating positions"); // iterate through all components for entities with data in both // position and velocity resources ctx.iter_r1w1(velocities, positions).components(|entity, v, p| { p.x += v.x; p.y += v.y; p.z += v.z; }); }); scope.run_r2w0(|ctx, names: &DebugNames, positions: &Positions| { println!("Printing positions"); // iterate through all entity IDs for entities with data in both // `names` and `positions` ctx.iter_r2w0(names, positions).entities(|entity_iter, n, p| { // `n` and `p` allow (potentially mutable) access to entity data inside // the resource without the ability to add or remove entities from the resource // - which would otherwise invalidate the iterator for e in entity_iter { println!("Entity {} is at {:?}", n.get(e).unwrap().name, p.get(e).unwrap()); } }); }); }); world.run(&mut update);
Parallel System Execution
Systems queued into a command buffer within a single call to queue_systems
may be executed
in parallel by the world.
The order in which systems are queued is significant in one way: the scheduler guarantees that any changes to resources will always be observed in the same order in which systems were queued.
For example, given two systems - ReadPositions
and WritePositions
- if WritePositions was
queued before ReadPositions, then it is guarenteed that ReadPositions will see any changes
made by WritePositions. Conversely, if the order were to be swapped, then ReadPositions
is guaranteed to not observe the changes made by WritePositions.
There is one exception to this. Entity deletions are committed when all concurrently executing
systems have completed. This behavior is deterministic, but not always obvious. If you wish to
ensure that entity deletions from one system are always seen by a later system, then queue
the two systems in separate queue_systems
calls.
Modules
bitset | |
join |
Structs
Entities |
Manages the allocation and delection of |
EntitiesTransaction |
An entity transaction allows concurrent creations and deletions of entities
from an |
Entity |
A handle onto an entity in a scene. |
EntityChangeSet |
Summarises the final changes made during the lifetime of an entity transaction. |
EntityIter |
An iterator which converts indexes into entitiy IDs. |
EntityIteratorBuilder |
Provides methods for efficiently iterating through entity resources. |
MapResource |
A |
MapStorage |
Provides methods to retrieve and mutate entity data
stored inside a |
ResourceBuilder |
Constructs and configures a world resource. |
SystemCommandBuffer |
Records system executions, to be run later within a |
SystemContext |
Contains system execution state information. |
SystemScope |
Systems queued within a |
VecResource |
A |
VecStorage |
Provides methods to retrieve and mutate entity data stored inside a |
VecStorageIter |
An iterator over entity data stored in a |
VecStorageIterMut |
An iterator over entity data stored in a |
World |
Stores entities are resources, and provides mechanisms to update the world state via systems. |
Enums
SequentialExecute |
Determines the behavior entity transaction commits when running a system command buffer sequentially. |
Traits
ComponentResourceApi |
A component resource is a resource which stores data related to entities
in the form of a single |
EntityResource |
An entity resource is a resource which stores data about entities. |
Handle |
A handle is formed out of an Index and a Generation |
Resource |
A resource whos system access is controlled by the |
Type Definitions
Generation |
Generation is incremented each time an index is re-used. |
Index |
Only one entity with a given index may be alive at a time. |