shadow cascades where not calculated properly because part of the
calculation took the cascade near/far into account, while another
part didn't. This resulted in cascades being too large. It didn't
create wrong shadows, but reduced (and in some case canceled) the
usefulness of the cascade.
We fix the problem by always using the projection matrix only for
describing the cascade's frustum, as opposed to just passing the
near/far plane distances.
Now the calculation of each cascade is completely self contained and
identical.
We also improve the orientation of the light frustum:
We can rotate the light frustum around the light direction axis, so
it aligns with the view direction, this generally result in smaller
light frustums. This cannot be used in stable mode.
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