# Objective
Fixes https://github.com/bevyengine/bevy/issues/9077 (see this issue for
motivations)
## Solution
Implement 1 and 2 of the "How to fix it" section of
https://github.com/bevyengine/bevy/issues/9077
`update_directional_light_cascades` is split into
`clear_directional_light_cascades` and a generic
`build_directional_light_cascades`, to clear once and potentially insert
many times.
---
## Changelog
`DirectionalLight`'s computation is now generic over `CameraProjection`
and can work with custom camera projections.
## Migration Guide
If you have a component `MyCustomProjection` that implements
`CameraProjection`:
- You need to implement a new required associated method,
`get_frustum_corners`, returning an array of the corners of a subset of
the frustum with given `z_near` and `z_far`, in local camera space.
- You can now add the
`build_directional_light_cascades::<MyCustomProjection>` system in
`SimulationLightSystems::UpdateDirectionalLightCascades` after
`clear_directional_light_cascades` for your projection to work with
directional lights.
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Co-authored-by: Carter Anderson <mcanders1@gmail.com>
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