What it does say is that you must move directly towards the target, and that your movement cannot be hindered. In the case of tonight's game, black tentacles didn't hamper Cefn's movement, and thus where not difficult terrain for him. Also given that all three squares in front of the enemy where equidistant any of the three squares where valid charge end points. I then must take the most direct route to that square, whether you take the diagonal at the beginning or end of the of the movement it doesn't matter since either path is the most direct path to the charge target square.Movement During a Charge: You must move before your attack, not after. You must move at least 10 feet (2 squares) and may move up to double your speed directly toward the designated opponent. If you move a distance equal to your speed or less, you can also draw a weapon during a charge attack if your base attack bonus is at least +1. You must have a clear path toward the opponent, and nothing can hinder your movement (such as difficult terrain or obstacles). You must move to the closest space from which you can attack the opponent. If this space is occupied or otherwise blocked, you can’t charge. If any line from your starting space to the ending space passes through a square that blocks movement, slows movement, or contains a creature (even an ally), you can’t charge. Helpless creatures don’t stop a charge.
PS Animal Focus does not call it out, but Feral Focus is called out as a polymorph affect. The key wording is on page 211 of the CRB:
You can only be affected by one polymorph spell at a time. If a new polymorph spell is cast on you (or you activate a polymorph effect, such as wild shape), you can decide whether or not to allow it to affect you, taking the place of the old spell. In addition, other spells that change your size have no effect on you while you are under the effects of a polymorph spell.