ReactiveECS.jl v3: Reconciling Performance and Flexibility

A high-performance, modular, event-driven and fragment-vector based ECS (Entity-Component-System) architecture written in Julia. Designed for game engines, simulations, or any data-oriented architecture needing maximum performances with extreme flexibility.

It's already used by the highly flexible 2D/3D game engine Cruise.jl one of his core architecture

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Installation

julia> ]add ReactiveECS

For development version

julia> ] add https://github.com/Gesee-y/ReactiveECS.jl

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Characteristics and Features

• Fast: One of the fastest ECS in Julia, already outperforming some well-established C/C++ ECS. See this.
• Unique memory layout: With a custom data structure named fragment vectors.
• Maximum memory locality: Using partitions which are range of data, it makes sure entities are tighly packed in memory, allowing vectorization.
• Efficient structural changes: With fragment vectors which allow fast entities/components add/remove.
• Performant random access iteration: With optimized blocks iterators from fragment vectors.
• Flexible: Add, remove, or chain systems at runtime, you can even inject a system in the middle of a chain.
• Changes tracking: Optionally watch changes on a field of component.
• Granular concurrency safety: Provides specialized tools like HierarchicalLock to help you cleanly manage concurrency.
• Inherently ready for parallelism: Its partitioned table already acts as chunks for parallel processing with cycles detection.
• Easy to use: Thanks to Julia’s powerful macros, which abstract away complexity.
• Allow lazy operations: Such as lazy entities creation or lazy resizing.
• Multiple components per entities: Through multiple tables and foreign keys.
• No memory movements once stable: Once the ECS reached its peak, no more allocations or desallocations.

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Example

using ReactiveECS

# Define component
@component Position begin
    x::Float64
    y::Float64
end

# Define system
@system MoveSystem begin
    dt::Float32
end

function ReactiveECS.run!(world, sys::MoveSystem, query::Query)
    positions = get_component(world, :Position)  # Get all Position components
    dt = sys.dt

    @foreachrange query begin
        pblock = get_block(positions, range)
        r = offset(range, get_offset(positions, range)
        for i in r
            pos = pblock[i]
            pblock[i] = Position(pos.x+dt, pos.y)  # Move entity along x-axis
        end
    end
    return positions  # Pass data to listeners
end

# Setup
world = ECSManager()
move_sys = MoveSystem(0.1)

subscribe!(world, move_sys, @query(world,Position))
run_system!(move_sys)

# Create entity
entity = create_entity!(world; Position=PositionComponent(0.0, 0.0))

# Run for 3 frames
for frame in 1:3
    println("Frame $frame: x=$(entity.Position.x)")
    dispatch_data(world)
    blocker(world)
end

License

MIT License © 2025 [Kaptue Talom Lael]

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Contributing

PRs and issues are welcome. Feel free to open discussions if you plan to adapt this ECS for your own game engine or simulation framework.

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Contact

For technical questions, ideas, or contributions:

Email: gesee37@gmail.com