gaemstone.ECS

.. is a medium-level managed wrapper library around the flecs-cs bindings for the amazing Entity Component System (ECS) framework Flecs. It is used as part of the gæmstone game engine, but may be used in other projects as well. To efficiently use this library, a thorough understanding of Flecs is required.

Features

These classes have only recently been split from the main gæmstone project. It is currently unclear what functionality belongs where, and structural changes are still very likely. In its current state, feel free to use gæmstone.ECS as a reference for building similar projects, or be aware that things are in flux, and in general nowhere near stable.

• Simple wrapper structs such as Entity and Identifier.
• Classes with convenience functions like EntityRef and EntityType.
• EntityPath uses a unix-like path, for example /Game/Players/copygirl.
• Define your own Components as both value or reference types.
• Query the ECS with Iterators, Filters, Queries and Rules.
• Create Systems for game logic and Observers to act on changes.

Example

var world = new World();

var position = world
	.New("Position")    // Create a new EntityBuilder, and set its name.
	.Symbol("Position") // Set entity's symbol. (Used in query expression.)
	.Build()            // Actually create the entity in-world.
	// Finally, create a component from this entity.
	// "Position" is defined at the bottom of this example.
	.InitComponent<Position>();

// Create an "Entities" parent with two positioned entities inside.
var entities = world.New("Entities").Build();
entities.NewChild("One").Set(new Position(-5,  0)).Build();
entities.NewChild("Two").Set(new Position(10, 20)).Build();

// Changed my mind: Let's multiply each entity's position by 10.
foreach (var child in entities.GetChildren()) {
  ref var pos = ref child.GetRefOrThrow<Position>();
  pos = new(pos.X * 10, pos.Y * 10);
}

var onUpdate = world.LookupByPathOrThrow("/flecs/pipeline/OnUpdate");

// Create a system that will move all entities with
// the "Position" component downwards by 2 every frame.
world.New("FallSystem").Build()
	.InitSystem(onUpdate, new("Position"), iter => {
		var posColumn = iter.Field<Position>(1);
		for (var i = 0; i < iter.Count; i++) {
			ref var pos = ref posColumn[i];
			pos = new(pos.X, pos.Y + 2);
		}
	});

// Create a system that will print out entities' positions.
world.New("PrintPositionSystem").Build()
	.InitSystem(onUpdate, new("[in] Position"), iter => {
		var posColumn = iter.Field<Position>(1);
		for (var i = 0; i < iter.Count; i++) {
			var entity = iter.Entity(i);
			var pos    = posColumn[i];
			Console.WriteLine($"{entity.Name} is at {pos}");
		}
	});

// Infinite loop that runs the "game" at 30 FPS.
while (true) {
	var delta = TimeSpan.FromSeconds(1.0f / 30);
	// Progress returns false if quit was requested.
	if (!world.Progress(delta)) break;
	Thread.Sleep(delta);
}

record struct Position(int X, int Y);

Instructions

# Clone the repository. Recurse into submodules to include flecs-cs and flecs.
git clone --recurse-submodules https://git.mcft.net/copygirl/gaemstone.ECS.git

# If you want to add it to your own repository as a submodule:
git submodule add https://git.mcft.net/copygirl/gaemstone.ECS.git

# To add a reference to this library to your .NET project:
dotnet add reference gaemstone.ECS/src/gaemstone.ECS/gaemstone.ECS.csproj

# To generate flecs-cs' bindings:
./gaemstone.ECS/src/flecs-cs/library.sh