ecs_pattern 🚀

Implementation of the ECS pattern for creating games.

Make a game instead of architecture for a game.

Документация на Русском.

Python version	3.3+
License	Apache-2.0
PyPI	https://pypi.python.org/pypi/ecs_pattern/
Dependencies	dataclasses before 3.7, typing before 3.5

Intro

ECS - Entity-Component-System - it is an architectural pattern created for game development.

It is great for describing a dynamic virtual world.

Basic principles of ECS:

• Composition over inheritance
• Data separated from logic (Data Oriented Design)

Component - Property with object data
Entity - Container for properties
System - Data processing logic
EntityManager - Entity database
SystemManager - Container for systems

Installation

$ pip install ecs-pattern

Guide

from ecs_pattern import component, entity, EntityManager, System, SystemManager

• Describe components - component
• Describe entities based on components - entity
• Distribute the responsibility of processing entities by systems - System
• Store entities in entity manager - EntityManager
• Manage your systems with SystemManager

Component

Property with object data. Contains only data, no logic.

The component is used as a mixin in entities.

Use the ecs_pattern.component decorator to create components.

Technically this is python dataclass.

@component
class ComPosition:
    x: int = 0
    y: int = 0

@component
class ComPerson:
    name: str
    health: int

Entity

Container for properties. Consists of components only.

It is forbidden to add attributes to an entity dynamically.

Use the ecs_pattern.entity decorator to create entities.

Technically this is python dataclass with slots=True.

@entity
class Player(ComPosition, ComPerson):
    pass

@entity
class Ball(ComPosition):
    pass

System

Entity processing logic.

Does not contain data about entities and components.

Use the ecs_pattern.System abstract class to create concrete systems:

class SysInit(System):
    def __init__(self, entities: EntityManager):
        self.entities = entities

    def start(self):
        self.entities.init(
            TeamScoredGoalEvent(Team.LEFT),
            Spark(spark_sprite(pygame.display.Info()), 0, 0, 0, 0)
        )
        self.entities.add(
            GameStateInfo(play=True, pause=False),
            WaitForBallMoveEvent(1000),
        )

class SysGravitation(System):
    def __init__(self, entities: EntityManager):
        self.entities = entities

    def update(self):
        for entity_with_pos in self.entities.get_with_component(ComPosition):
            if entity_with_pos.y > 0:
                entity_with_pos.y -= 1

EntityManager

Entity database.

A single point of access to all entities.

Use the ecs_pattern class.EntityManager for creating an entity manager.

Time complexity of get_by_class and get_with_component - like a dict

entities.add - Add entities.

entities.delete - Delete entities.

entities.delete_buffer_add - Save entities to the delete buffer to delete later.

entities.delete_buffer_purge - Delete all entities in the deletion buffer and clear the buffer.

entities.init - Let manager know about entities. KeyError are raising on access to unknown entities.

entities.get_by_class - Get all entities of the specified classes. Respects the order of entities.

entities.get_with_component - Get all entities with the specified components.

entities = EntityManager()
entities.add(
    Player('Ivan', 20, 1, 2),
    Player('Vladimir', 30, 3, 4),
    Ball(0, 7)
)
for entity_with_pos in self.entities.get_with_component(ComPosition):
    print(entity_with_pos.x, entity_with_pos.y)
for player_entity in entities.get_by_class(Player):
    print(player_entity.name)
    entities.delete_buffer_add(player_entity)
entities.delete_buffer_purge()
entities.delete(*tuple(next(entities.get_by_class(Ball), [])))

SystemManager

Container for systems.

Works with systems in a given order.

Use the ecs_pattern.SystemManager class to manage systems.

system_manager.start_systems - Initialize systems. Call once before the main systems update cycle.

system_manager.update_systems - Update systems status. Call in the main loop.

system_manager.stop_systems - Stop systems. Call once after the main loop completes.

entities = EntityManager()
entities.add(
    Player('Ivan', 20, 1, 2),
    Player('Vladimir', 30, 3, 4),
    Ball(0, 7)
)
system_manager = SystemManager([
    SysPersonHealthRegeneration(entities),
    SysGravitation(entities)
])
system_manager.start_systems()
while play:
    system_manager.update_systems()
    clock.tick(24)  # *pygame clock
system_manager.stop_systems()

Examples

• Pong game: pygame + ecs_pattern.

Advantages

• Weak code cohesion - easy to refactor and expand the codebase
• Modularity and testability of logic - easy to test and reuse code in other projects
• Hard to write bad code
• Easy to follow Single Responsibility logic
• Easy to combine entity properties
• Easy to analyze performance
• Easy to parallelize processing
• Easy to work with clean data

Difficulties

It can take a lot of practice to learn how to cook ECS properly:

• Data is available from anywhere - hard to find errors
• Systems work strictly one after another
• Recursive logic is not directly supported

Newbie mistakes

• Inheritance of components, entities, systems
• Ignoring the principles of ECS, such as storing data in the system
• Raising ECS to the absolute, no one cancels the OOP
• Adaptation of the existing project code under ECS "as is"
• Use of recursive or reactive logic in systems
• Using EntityManager.delete in get_by_class, get_with_component loops

Good Practices

• Use components - flags
• Minimize component change locations
• Use event entities and event systems
• Do not use methods in components and entities

Releases

History of important changes: release_notes.rst

Help the project

• Found a bug or have a suggestion - issue / merge request 🎯
• There is nothing to help this project with - help another open project that you are using ✋
• Nowhere to put the money - spend it on family, friends, loved ones or people around you 💰
• Star the project ⭐