# Objective
Because of mesh preprocessing, users cannot rely on
`@builtin(instance_index)` in order to reference external data, as the
instance index is not stable, either from frame to frame or relative to
the total spawn order of mesh instances.
## Solution
Add a user supplied mesh index that can be used for referencing external
data when drawing instanced meshes.
Closes#13373
## Testing
Benchmarked `many_cubes` showing no difference in total frame time.
## Showcase
https://github.com/user-attachments/assets/80620147-aafc-4d9d-a8ee-e2149f7c8f3b
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Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
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