Geary

Overview

Geary is an Entity Component System (ECS) written in Kotlin. The engine design is inspired by flecs. Core parts of the engine (ex. system iteration, entity creation) are quite optimized, with the main exception being our event system. We use Geary internally for our Minecraft plugins, see geary-papermc for more info.

Features

• Null safe component access
• Flecs-style entity relationships alice.addRelation<FriendsWith>(bob)
• Fully type safe system definition
• Prefabs that reuse components across entities
• Persistent components and loading prefabs from files thanks to kotlinx.serialization
• Addon system to use only what you need

Example

A simple ssytem that iterates over all entities with a position and velocity, updating the position every engine tick.

data class Position(var x: Double, var y: Double)
data class Velocity(var x: Double, var y: Double)

class UpdatePositionSystem : TickingSystem(interval = 20.milliseconds) {
    // Specify all components we want (Geary also supports branched AND/OR/NOT statements for selection)
    val Pointer.position by get<Position>()
    val Pointer.velocity by get<Velocity>()

    override fun Pointer.tick() {
        // We can access our components like regular variables!
        position.x += velocity.x
        position.y += velocity.y
    }
}

fun main() {
    // Set up geary
    geary(ArchetypeEngineModule) {
        // configure engine here
        install(Prefabs)
    }

    geary.pipeline.addSystem(UpdatePositionSystem())

    // Create an entity the system can run on
    entity {
        setAll(Position(0.0, 0.0), Velocity(1.0, 0.0))
    }
}

Usage

A WIP wiki can be found at wiki.mineinabyss.com

Gradle

repositories {
    maven("https://repo.mineinabyss.com/releases")
}

dependencies {
    val gearyVersion = "x.y.z"
    implementation("com.mineinabyss:geary-core:$gearyVersion")
    implementation("com.mineinabyss:geary-<addon-name>:$gearyVersion")
}

Roadmap

As the project matures, our primary goal is to make it useful to more people. Here are a handful of features we hope to achieve:

• Multiplatform support, with js, jvm, and native targets
• Publish numbers for benchmarks and cover more parts of the engine with them
• Component data migrations
• Complex queries (including relations like parent/child)