Typically, when VOPs cook geometry, the SOPs will try to do the right thing with the normal attribute. That is, if the P attribute is modified, the normal attribute will usually be out of date. The right thing is usually to re-compute the point normals whenever P changes (provided the VEX code doesn’t modify N on its own).

However, in some cases, you may want finer control over how the normal attribute is handled. There are three possible choices provided:

1. No modification to N:

   The VEX code will leave the N attribute unchanged.

2. Re-compute N if P changes (default):

   The VEX code will recompute the N attribute, if the P attribute is changed.

3. Forcibly recompute N:

   The VEX code will recompute normals, regardless of whether P is modified.