You have to check LoS when you check range, when making an attack or casting a spell. If you do not have LoS then that target is not a legal target of the attack / spell
I thought it was "You have to check LoS when you TARGET something for an attack or spell casting."
i.e. Calculating range does not require a LoS, but targeting an object does.
That is the nuisance we have been using in our games.
Any and everytime you count range, LoS is also checked.
From page 17 of the Core rules:
LINE OF SIGHT
In order to cast a spell or make a ranged attack
against a target, you must have a clear “line of sight”
(called “LoS” for short). Normally, a creature has LoS
to the entire game board, even into zones that are
out of range. But, some walls block LoS. You cannot
cast a spell or make a ranged attack through a wall
that blocks LoS.
When you count range to your target, you must also
check if you have clear line of sight (LoS). Draw an
imaginary straight line from the center of the attacker’s
or caster’s zone to the center of the target’s zone. LoS
is blocked if the line crosses through a zone border
that has a wall on it with the blocks LoS trait. Walls do
not normally block LoS if the line crosses diagonally
through the corner of a wall border, as long as at least
one side of that corner does not block LoS. When
drawing LoS to a wall, draw it to the center of the
zone border.
