struct WorldTransform{
    fmat4 matrix;
};
struct LocalTransform{
    fmat4 matrix;
}
struct Parent{
    ecs::Entity entity;
}
const int Geometry = 1234 // whatever, must be unique

    // ...

ecs::Archetype geometryArchetype;
geometryArchetype.add<WorldTransform>();
geometryArchetype.add<LocalTransform>();
geometryArchetype.add<Parent>();
geometryArchetype.addTag(Geometry);

// more on the ecsCommands later
auto geom = ecsCommands->createEntity(geometryArchetype);

WorldTransform& tr = geom.getComponent<WorldTransform>();
math::setTranslation(tr.matrix, fvec3(1.0f, 1.0f, 1.0f));

     // ...