Example usage with some random Engine

```rust struct App { window: Window, ws: WindowState, update_loop: UpdateLoop, }

impl App { fn init(target: &EventLoopTarget) -> Self { let window = WindowBuilder::new().build(target).unwrap(); let ws = WindowState::new(&window); let update_loop = UpdateLoop::new(UpdateRate::PerSecond(60));

    Self {
        window,
        ws,
        update_loop,
    }
}

}

impl Runnable for App { fn event(&mut self, event: Event, _: &EventLoopTarget, control: &mut ControlFlow) { self.ws.event(&event);

    if self.ws.should_close {
        *control = ControlFlow::Exit;
    }
}

fn draw(&mut self) {
    self.update_loop.update(|| {
        // update();
    });

    // draw();
}

}

main_app!(App); ```