Change colour on a StandardMaterial

[joebain]

I'm trying to change the colour on a StandardMaterial. I had this working previously by using a query to get the material reference:
mut query: Query<(&mut Enemy, &mut Handle<StandardMaterial>)>,
and then swapping the material for a different colour one:

 for (mut enemy, mut mat_handle) in &mut query {
    *mat_handle = coloured_mat;
}

however I had to make my PbrBundle a child of the Enemy component because I needed to apply a scale and rotation offset. Now I can't get the material handle through the query and I can't work out how to solve this. In other engines I would expect to be able to keep a reference to the material on my Enemy and then set the base_colour to another one at runtime. I'm not sure if this is possible with Bevy but I'm getting tripped up by the borrow / move / copy restrictions. (I'm new to Rust too, sorry.)

Edit:
To clarify the other approach I tried, I have my Enemy struct with a material handle on it:

#[derive(Component)]
pub struct Enemy {
    orbit_speed: f32,
    move_speed: f32,
    material: Handle<StandardMaterial>,
}

Then I get the material from the asset resource and set the base_color. This compiles but the colour doesn't change when I run it.

let enemy_mat = materials.get_mut(&enemy.material);
match enemy_mat {
    Some(m) => {
        m.base_color = new_col;
    }
    None => {}
}

[wilk10]

The first setup doesn't work any more because now the entity with the PbrBundle is a child of Enemy, whose Entity is stored in the Children component. So to access the material handle, you now need two queries:

fn change_material(
    enemies: Query<&Children, With<Enemy>>,
    mut standard_materials: Query<&mut Handle<StandardMaterial>> ,
) { 
    for children_of_enemy in enemies.iter() {
        for child in children_of_enemy.iter() {
            if let Ok(handle) = standard_materials.get_mut(child) {
                // etc
            }
        }
    }
}

In the second case it doesn't work because you need to substitute the Handle, not mutate the colour. If you change the colour, you need to add the changed material to materials, get the new handle and assign the handle to the entity with Enemy, so it's much better to prepare the materials in advance, save the handles somewhere, like you did inside Enemy, and access / assign them when needed.

Hope it was helpful!

[joebain]

Thanks, that's helpful. The only thing I don't understand now, if I use that query to get Children of an Enemy how can I also get a reference to the Enemy too? I need to set the material based on the state of the Enemy.

[tim-blackbird]

fn change_material(
    enemies: Query<(&Children, &Enemy)>,
    mut standard_materials: Query<&mut Handle<StandardMaterial>> ,
) { 
    for (children, enemy) in &enemies {
        for child in children {
            if let Ok(handle) = standard_materials.get_mut(*child) {
                // etc
            }
        }
    }
}