Tainted \\ Coders

Custom System Params

Last updated:

We can reduce the argument counts and control access to our queries by making custom SystemParam. A system param is valid as long as each field of its struct is also a SystemParam like a Query, Resource, etc.

Its easy to do this using the #[derive(SystemParam)]

struct SizeParams<'w, 's> {
    images: ResMut<'w, Assets<Image>>,
    primary_window_query: Query<'w, 's, &'static Window, With<PrimaryWindow>>,
    windows_query: Query<'w, 's, &'static Window>,

fn print_image_sizes(sizes: SizeParams) {
    for image in sizes.images {
        // ...

Read more