Definition

It is a type of data that has only one single instance. Such as configuration / settings.
Resource is independent with Entity.

Resource declaration

To create a resource type, use trait Resource for the Struct:

#[derive(Resource)]
struct WindowSettings {
	title: String,
	resolution: (f64, f64),
}

Next we have two ways to add resource to our app:
With Command:

fn setup (
	mut commands: Commands
) {
	commands.insert_resource(WindowSettings { title: "Bevy".into(), resoultion: (500., 300.)});
}

By app builder:

fn main()
{
	App::new()
		.insert_resource(WindowSettings { title: "Bevy".into(), resoultion: (500., 300.)})
		.run();
}

Resource accessing

fn system(
	my_resource: Res<MyResource>,
	my_mut_resource: ResMut<MyMutResource>,
)