Macro bind_mat 

macro_rules! bind_mat {
    ($pass:expr, $materials:expr, $handle:expr) => { ... };
}

The “look up, then bind” chain every draw call repeats: $materials.get($handle), then set_pipeline + set_bind_group(0, ...) on $pass. Returns from the enclosing function (via or_return!) if the lookup isn’t ready yet — an asset that hasn’t finished uploading is a normal, common case (a couple frames on load), not a bug.

Evaluates to the looked-up &GPUMaterial, so callers that also need .update(name, data) on it (e.g. a per-frame camera uniform) can still bind that:

let material = bind_mat!(render_pass, materials, material_handle);