Zig ECS Archetypes

component.zig

const std = @import("std");
const Vector2 = @import("raylib").Vector2;

pub const Velocity = Component(0x00000001, "velocity", Vector2);

pub const Position = Component(0x00000002, "position", struct {
    x_y: Vector2,
    z: f32,
});

pub const Collision = Component(0x00000004, "collision", struct {
    offset: Vector2,
    width: f32,
    height: f32,
});

fn Component(comptime _bit_flag: u32, comptime _name: [:0]const u8, comptime T: type) type {
    return struct {
        const Self = @This();
        pub const bit_flag = _bit_flag;
        pub const Type: type = T;
        pub const name: [:0]const u8 = _name;
    };
}

pub fn Bundle(comptime w: anytype, comptime components: anytype) struct { u16, type, type } {
    var fields: [components.len]std.builtin.Type.StructField = undefined;

    const decls: [0]std.builtin.Type.Declaration = .{};

    comptime var bundle_bit: u32 = 0x00000000;

    inline for (components, 0..) |comp, idx| {
        bundle_bit = bundle_bit | comp.bit_flag;
        fields[idx] = std.builtin.Type.StructField{
            .alignment = @alignOf(comp.Type),
            .type = comp.Type,
            .is_comptime = false,
            .name = comp.name,
            .default_value_ptr = null,
        };
    }

    const entity_type: std.builtin.Type.Struct = .{
        .layout = .auto,
        .is_tuple = false,
        .fields = &fields,
        .decls = &decls,
    };

    const EntityType: type = @Type(.{ .@"struct" = entity_type });

    const Builder: type = struct {
        // pub fn createEntity(_w: w, entity: EntityType) void {
        //     inline for (components) |comp| {
        //         @field(_w, comp.name)[entity_id] = @field(entity, comp.name);
        //     }
        // }
        pub fn getEntity(_w: w, comptime b: u32, entity_id: usize) EntityType {
            if (b != bundle_bit) {
                @compileError("Incorrect bitset for entity");
            }

            var entity: EntityType = undefined;
            inline for (components) |comp| {
                @field(entity, comp.name) = @field(_w, comp.name)[entity_id].?;
            }

            return entity;
        }
    };

    return .{ bundle_bit, EntityType, Builder };
}