Crate specs

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SPECS Parallel ECS

This library provides an ECS variant designed for parallel execution and convenient usage. It is highly flexible when it comes to actual component data and the way it is stored and accessed.

Features:

  • depending on chosen features either 0 virtual function calls or one per system
  • parallel iteration over components
  • parallel execution of systems

High-level overview

One could basically split this library up into two parts: The data part and the execution part.

The data

World is where component storages, resources and entities are stored. See the docs of World for more.

Components can be easily implemented like this:

use specs::prelude::*;

struct MyComp;

impl Component for MyComp {
    type Storage = VecStorage<Self>;
}

Or alternatively, if you enable the "derive" feature, you can use a custom #[derive] macro:


use specs::{prelude::*, Component};

#[derive(Component)]
#[storage(VecStorage)] // default is `DenseVecStorage`
struct MyComp;

You can choose different storages according to your needs.

These storages can be joined together, for example joining a Velocity and a Position storage means you’ll only get entities which have both of them. Thanks to rayon, this is even possible in parallel! See ParJoin for more.

System execution

Here we have System and Dispatcher as our core types. Both types are provided by a library called shred.

The Dispatcher can be seen as an optional part here; it allows dispatching the systems in parallel, given a list of systems and their dependencies on other systems.

If you don’t like it, you can also execute the systems yourself by using RunNow.

Systems are traits with a run() method and an associated SystemData, allowing type-safe aspects (knowledge about the reads / writes of the systems).

Examples

This is a basic example of using Specs:

extern crate specs;

use specs::prelude::*;

// A component contains data which is
// associated with an entity.

struct Vel(f32);

impl Component for Vel {
    type Storage = VecStorage<Self>;
}

struct Pos(f32);

impl Component for Pos {
    type Storage = VecStorage<Self>;
}

struct SysA;

impl<'a> System<'a> for SysA {
    // These are the resources required for execution.
    // You can also define a struct and `#[derive(SystemData)]`,
    // see the `full` example.
    type SystemData = (WriteStorage<'a, Pos>, ReadStorage<'a, Vel>);

    fn run(&mut self, (mut pos, vel): Self::SystemData) {
        // The `.join()` combines multiple components,
        // so we only access those entities which have
        // both of them.

        // This joins the component storages for Position
        // and Velocity together; it's also possible to do this
        // in parallel using rayon's `ParallelIterator`s.
        // See `ParJoin` for more.
        for (pos, vel) in (&mut pos, &vel).join() {
            pos.0 += vel.0;
        }
    }
}

fn main() {
    // The `World` is our
    // container for components
    // and other resources.

    let mut world = World::new();
    world.register::<Pos>();
    world.register::<Vel>();

    // An entity may or may not contain some component.

    world.create_entity().with(Vel(2.0)).with(Pos(0.0)).build();
    world.create_entity().with(Vel(4.0)).with(Pos(1.6)).build();
    world.create_entity().with(Vel(1.5)).with(Pos(5.4)).build();

    // This entity does not have `Vel`, so it won't be dispatched.
    world.create_entity().with(Pos(2.0)).build();

    // This builds a dispatcher.
    // The third parameter of `add` specifies
    // logical dependencies on other systems.
    // Since we only have one, we don't depend on anything.
    // See the `full` example for dependencies.
    let mut dispatcher = DispatcherBuilder::new().with(SysA, "sys_a", &[]).build();

    // This dispatches all the systems in parallel (but blocking).
    dispatcher.dispatch(&mut world);
}

You can also easily create new entities on the fly:

use specs::prelude::*;

struct EnemySpawner;

impl<'a> System<'a> for EnemySpawner {
    type SystemData = Entities<'a>;

    fn run(&mut self, entities: Entities<'a>) {
        let enemy = entities.create();
    }
}

See the repository’s examples directory for more examples.

Re-exports

Modules

  • changeset
    Provides a changeset that can be collected from an iterator.
  • error
    Specs errors
  • join
    Joining of components for iteration over entities with specific components.
  • prelude
    Prelude module
  • saveload
    Save and load entities from various formats with serde.
  • storage
    Component storage types, implementations for component joins, etc.
  • world
    Entities, resources, components, and general world management.

Structs

  • AsyncDispatcher
    Like, Dispatcher but works asynchronously.
  • BatchAccessor
    The BatchAccessor is used to notify the main dispatcher of the read and write resources of the Systems contained in the batch (“sub systems”).
  • BatchUncheckedWorld
    The BatchUncheckedWorld wraps an instance of the world. You have to specify this as SystemData for a System implementing BatchController.
  • BitSet
    A BitSet is a simple set designed to track which indices are placed into it.
  • Dispatcher
    The dispatcher struct, allowing systems to be executed in parallel.
  • DispatcherBuilder
    Builder for the Dispatcher.
  • Read
    Allows to fetch a resource in a system immutably.
  • ReaderId
    A reader ID which represents a subscription to the events pushed to the EventChannel.
  • StaticAccessor
    The static accessor that is used for SystemData.
  • World
    A Resource container, which provides methods to insert, access and manage the contained resources.
  • Write
    Allows to fetch a resource in a system mutably.

Enums

Traits

  • Accessor
    A trait for accessing read/write multiple resources from a system. This can be used to create dynamic systems that don’t specify what they fetch at compile-time.
  • BatchController
    The BatchController describes things that allow one to control how batches of systems are executed.
  • RunNow
    Trait for fetching data and running systems. Automatically implemented for systems.
  • System
    A System, executed with a set of required Resources.
  • SystemData
    A static system data that can specify its dependencies at statically (at compile-time). Most system data is a SystemData, the DynamicSystemData type is only needed for very special setups.

Type Aliases

  • ReadExpect
    Allows to fetch a resource in a system immutably. This will panic if the resource does not exist. Usage of Read or Option<Read> is therefore recommended.
  • WriteExpect
    Allows to fetch a resource in a system mutably. This will panic if the resource does not exist. Usage of Write or Option<Write> is therefore recommended.

Derive Macros