m110 / donburi

Just another ECS library for Ebitengine

Donburi

Donburi is just another Entity Component System library for Ebitengine inspired by legion.

It aims to be a feature rich and high performance ECS Library.

GoDoc

Contents

• Contents
• Features
• Examples
• Installation
• Getting Started
  • Worlds
  • Queries
  • Tags
  • Systems (Experimental)
• Optional Features
  • Math
  • Transform (Experimental)
  • Hierarchy (Experimental)
• Internal Design for World
• How to contribute?
• Contributors

Features

• It introduces the concept of Archetype, which allows us to query entities very efficiently based on the components layout.
• It is possible to combine And, Or, and Not conditions to perform complex queries for components.
• It avoids reflection on every frame for performance.
• Ability to dynamically add or remove components from an entity.
• APIs with Go Generics

There are many features that need to be added in the future (e.g., parent-child relationship, event-notification system etc).

Examples

To check all examples, visit this page.

The bunnymark example was adapted from mizu's code, which is made by sedyh.

Installation

go get github.com/yohamta/donburi

Getting Started

Worlds

import "github.com/yohamta/donburi"

world := donburi.NewWorld()

Entities can be created via either Create (for a single entity) or CreateMany (for a collection of entities with the same component types). The world will create a unique ID for each entity upon insertion that you can use to refer to that entity later.

// Component is any struct that holds some kind of data.
type PositionData struct {
  X, Y float64
}

type VelocityData struct {
  X, Y float64
}

// ComponentType represents kind of component which is used to create or query entities.
var Position = donburi.NewComponentType[PositionData]()
var Velocity = donburi.NewComponentType[VelocityData]()

// Create an entity by specifying components that the entity will have.
// Component data will be initialized by default value of the struct.
entity = world.Create(Position, Velocity);

// You can use entity (it's a wrapper of int64) to get an Entry object from World
// which allows you to access the components that belong to the entity.
entry := world.Entry(entity)

position := donburi.Get[PositionData](entry, Position)
velocity := donburi.Get[VelocityData](entry, Velocity)
position.X += velocity.X
position.Y += velocity.y

We can define helper functions to get components for better readability. This was advice from eliasdaler.

func GetPosition(entry *donburi.Entry) *PositionData {
  return donburi.Get[PositionData](entry, Position)
}

func GetVelocity(entry *donburi.Entry) *VelocityData {
  return donburi.Get[VelocityData](entry, Velocity)
}

Components can be added and removed through Entry objects.

// Fetch the first entity with PlayerTag component
query := query.NewQuery(filter.Contains(PlayerTag))
// Query.FirstEntity() returns only the first entity that 
// matches the query.
if entry, ok := query.FirstEntity(world); ok {
  donburi.Add(entry, Position, &PositionData{
    X: 100,
    Y: 100,
  })
  donburi.Remove(entry, Velocity)
}

Entities can be removed from World with the World.Remove() as follows:

if SomeLogic.IsDead(world, someEntity) {
  // World.Remove() removes the entity from the world.
  world.Remove(someEntity)
  // Deleted entities become invalid immediately.
  if world.Valid(someEntity) == false {
    println("this entity is invalid")
  }
}

Queries

Queries allow for high performance and expressive iteration through the entities in a world, to get component references, test if an entity has a component or to add and remove components.

You can search for entities that have all of a set of components.

// You can define a query by declaring what componet you want to find.
query := query.NewQuery(filter.Contains(Position, Velocity))

// You can then iterate through the entity found in the world
query.EachEntity(world, func(entry *donburi.Entry) {
  // An entry is an accessor to entity and its components.
  position := donburi.Get[PositionData](entry, Position)
  velocity := donburi.Get[VelocityData](entry, Velocity)
  
  position.X += velocity.X
  position.Y += velocity.Y
})

There are other types of filters such as And, Or, Exact and Not. You can combine them to find the target entities.

For example:

// This query retrieves entities that have an NpcTag and no Position component.
query := query.NewQuery(filter.And(
  filter.Contains(NpcTag),
  filter.Not(filter.Contains(Position))))

If you need to determine if an entity has a component, there is entry.HasComponent

For example:

// We have a query for all entities that have Position and Size, but also any of Sprite, Text or Shape.
query := query.NewQuery(
  filter.And(
    filter.Contains(Position, Size),
    filter.Or(
      filter.Contains(Sprite),
      filter.Contains(Text),
      filter.Contains(Shape),
    )
  )
)

// In our query we can check if the entity has some of the optional components before attempting to retrieve them
query.EachEntity(world, func(entry *donburi.Entry) {
  // We'll always be able to access Position and Size
  position := donburi.Get[PositionData](entry, Position)
  size := donburi.Get[SizeData](entry, Size)
  
  
  if entry.HasComponent(Sprite) {
    sprite := donburi.Get[SpriteData](entry, Sprite)
    // .. do sprite things
  }
  
  if entry.HasComponent(Text) {
    text := donburi.Get[TextData](entry, Text)
    // .. do text things
  }
  
  if entry.HasComponent(Shape) {
    shape := donburi.Get[ShapeData](entry, Shape)
    // .. do shape things
  }
  
})

Tags

You can attach one or multiple "Tag" components to an entity. "Tag"s are just components with no data.

Here is the utility function to create a tag component.

// This is the utility function to make tag component
func NewTag() *ComponentType {
  return NewComponentType(struct{}{})
}

Since "Tags" are components, they can be used in queries in the same way as components as follows:

var EnemyTag = donburi.NewTag()
world.CreateMany(100, EnemyTag, Position, Velocity)

// Search entities with EnemyTag
query := query.NewQuery(filter.Contains(EnemyTag))
query.EachEntity(world, func(entry *donburi.Entry) {
  // Perform some operation on the Entities with the EnemyTag component.
}

Systems (Experimental)

The ECS package provides so-called System feature in ECS which can be used together with a World instance.

See the GoDoc and Example.

How to create an ECS instance:

import (
  "github.com/yohamta/donburi"
  ecslib "github.com/yohamta/donburi/ecs"
)

world := donburi.NewWorld()
ecs := ecslib.NewECS(world)

A System is created from just a function that receives an argument (ecs *ecs.ECS).

// Some System's function
func SomeFunction(ecs *ecs.ECS) {
  // ...
}

ecs.AddSystem(
  ecs.System{
    Update: SomeFunction,
  }
)

You can also provide Draw() functions for Systems. The Layer option allows you to control the order of calling Draw() functions and where to render. An Layer is just an integer value from the user's perspective. The default value of Layer is just 0.

const (
  LayerBackground ecslib.LayerID = iota
  LayerActors
  LayerFX
)

ecs.AddSystem(
  ecs.System{
    Layer:  LayerBackground,
    Update: UpdateBackground,
    Draw:   DrawBackground,
  }
)

Execute an ECS's Update() and Draw() to run systems as below:

func (g *Game) Update() error {
  g.ecs.Update()
  return nil
}

func (g *Game) Draw(screen *ebiten.Image) {
  screen.Clear()
  g.ecs.DrawLayer(LayerBackground, screen)
  g.ecs.DrawLayer(LayerBunnies, screen)
  g.ecs.DrawLayer(LayerMetrics, screen)
}

The ecs.Create() and ecs.NewQuery() wrapper-functions allow you to create and query entities on a certain layer:

var layer0 ecs.LayerID = 0

// Create an entity on layer0
ecslib.Create(layer0, someComponents...)

// Create a query to iterate entities on layer0
queryForLayer0 := ecslib.NewQuery(layer0, filter.Contains(someComponent))

Example:

import (
  ecslib "github.com/yohamta/donburi/ecs"
  "github.com/yohamta/donburi/features/hierarchy"
)

const (
  LayerBackground ecs.LayerID = iota
  LayerBunnies
  LayerMetrics
)

func newECS() *ecs.ECS {
  world := donburi.NewWorld()
  ecs := ecslib.NewECS(world)

  ecs.AddSystems(
    // Systems are executed in the order they are added.
    ecs.System{
      Update: system.NewSpawn().Update,
    },
    ecs.System{
      Layer: LayerBackground,
      Draw:  system.DrawBackground,
    },
    ecs.System{
      Layer:  LayerMetrics,
      Update: metrics.Update,
      Draw:   metrics.Draw,
    },
    ecs.System{
      Update: system.NewBounce(&g.bounds).Update,
    },
    ecs.System{
      Update: system.Velocity.Update,
    },
    ecs.System{
      Update: system.Gravity.Update,
    },
    ecs.System{
      Layer: LayerBunnies,
      Draw:  system.Render.Draw,
    },
  )

  return ecs
}
// ...

func (g *Game) Update() error {
  g.ecs.Update()
  return nil
}

func (g *Game) Draw(screen *ebiten.Image) {
  screen.Clear()
  g.ecs.DrawLayer(LayerBackground, screen)
  g.ecs.DrawLayer(LayerBunnies, screen)
  g.ecs.DrawLayer(LayerMetrics, screen)
}

// ...

Optional Features

Math

The math package provides the basic types (Vec2 etc) and helpers.

See the GoDoc for more details.

Transform (Experimental)

The transofrm package provides the Tranform Component and helpers.

transform package allows us to handle position, rotation, scale data relative to the parent.

This package was adapted from ariplane's code, which is created by m110.

Usage:

w := donburi.NewWorld()

// setup parent
parent := w.Entry(w.Create(transform.Transform))
transform.Reset(parent) // Reset() initialize the transform data to be the default values

// set world position and scale for the parent
transform.SetWorldPosition(parent, dmath.Vec2{X: 1, Y: 2})
transform.SetWorldScale(parent, dmath.Vec2{X: 2, Y: 3})

// setup child
child := w.Entry(w.Create(transform.Transform))
donburi.SetValue(child, transform.Transform, transform.TransformData{
	LocalPosition: dmath.Vec2{X: 1, Y: 2},
	LocalRotation: 90,
	LocalScale:    dmath.Vec2{X: 2, Y: 3},
})

// add the child to the parent
transform.AppendChild(parent, child, false)

// get world position of the child with parent's position taken into account
pos := transform.WorldPosition(child)

// roatation
rot := transform.WorldRotation(child)

// scale
scale := transform.WorldScale(child)

How to remove chidren (= destroy entities):

// Remove children
transform.RemoveChildrenRecursive(parent)

// Remove children and the parent
transform.RemoveRecursive(parent)

Hierarchy (Experimental)

The hierarchy package provides the Parent-Children relationship function. Unlike transform package it doesn't have any data such as position or rotation.

See the GoDoc and Example.

Example:

import (
  ecslib "github.com/yohamta/donburi/ecs"
  "github.com/yohamta/donburi/features/hierarchy"
)

// ...

  Parent := donburi.NewTag().SetName("parent")
  Child := donburi.NewTag().SetName("child")

// ...

  parent := w.Entry(w.Create(Parent))
  child := w.Entry(w.Create(Child))

  // add a child
  hierarchy.AppendChild(parent, child)

  if children, ok := hierarchy.GetChildren(entry *donburi.Entry); ok {
    for _, c := range children {
      // do something
    }
  }

  // Remove children (= destroy entities)
  hierarchy.RemoveChildrenRecursive(parent)

  // Remove children and the parent
  hierarchy.RemoveRecursive(parent)
  
// ...

If you want children to be removed autoamtically when its parents are already removed:

// setup a world and ECS container
w := donburi.NewWorld()
ecs := ecslib.NewECS(w)

// Add system to remove children automatically
ecs.AddSystem(ecslib.System{
  Update: hierarchy.HierarchySystem.RemoveChildren,
})

Internal Design for World

It is a bit complex, so please refer to the following diagram to understand it.

How to contribute?

Feel free to contribute in any way you want. Share ideas, questions, submit issues, and create pull requests. Thanks!

Contributors

Made with contrib.rocks.