Fix error in volumetric fog shader

[rparrett]

Objective

Volumetric fog was broken by #13746.

Looks like this particular shader just got missed. I don't see any other instances of unpack_offset_and_counts in the codebase.

2024-12-06T03:18:42.297494Z ERROR bevy_render::render_resource::pipeline_cache: failed to process shader:
error: no definition in scope for identifier: 'bevy_pbr::clustered_forward::unpack_offset_and_counts'
    ┌─ crates/bevy_pbr/src/volumetric_fog/volumetric_fog.wgsl:312:29
    │
312 │     let offset_and_counts = bevy_pbr::clustered_forward::unpack_offset_and_counts(cluster_index);
    │                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unknown identifier
    │
    = no definition in scope for identifier: 'bevy_pbr::clustered_forward::unpack_offset_and_counts'

Solution

Use unpack_clusterable_object_index_ranges to get the indices for point/spot lights.

Testing

cargo run --example volumetric_fog
cargo run --example fog_volumes
cargo run --example scrolling_fog

[ecoskey]

LGTM! I didn't notice this change in the other PR, I'm glad we have a cleaner way to index clustered objects

[pcwalton]

Oops, sorry about that!