cullFace

If non-null, quad is coplanar with a block face which, if known, simplifiesor shortcuts geometric analysis that might otherwise be needed.Set to null if quad is not coplanar or if this is not known.Also controls face culling during block rendering.

Null by default.

When called with a non-null value, also sets nominalFace to the same value.

This is different than the value reported by getFace. That valueis computed based on face geometry and must be non-null in vanilla quads.That computed value is returned by lightFace.