Code was assuming frustrum planes are symmetrical which is not the case
for shifting. This lead to a shrinking region if shift was negative (and
a growing region if shift was positive)
So instead of only keeping track of plane on one side (and mirroring
over in code) get the actual planes after shifting and use these
instead.
This code corrects this for ortho and perspective cameras, it does not
touch panoramic cameras.
Reviewed By: brecht
Maniphest Tasks: T69911
Differential Revision: https://developer.blender.org/D9342
f76f48c3d3