Vision and Detection
Line of Sight
Losing Line of Sight or Line of Effect: Whenever a creature targets you with an ability or offensive action but loses line of sight or line of effect to you before the ability or offensive action takes effect, the creature may choose another valid target if able. If it does not, the action taken and resources used (such as spell slots) for that ability or offensive action are used with no effect.
A line of sight is a straight, unblocked line between two squares that indicates what a creature can clearly distinguish. Your line of sight normally extends only to [Long] range, however, you automatically attempt to establish line of sight to any creature within [Extreme] range that takes an offensive action that would affect a square you occupy. You may also attempt to establish line of sight to creatures currently within [Extreme] range by spending part of a move action to locate distant creatures. Beyond [Extreme] range, you cannot usually maintain line of sight.
Line of sight is blocked by solid barriers and similar limitations that affect normal sight, as well as the Stealth skill, and is limited by darkness, fog, smoke, and certain conditions. Some vision modes can establish line of sight through some of these barriers.
You are [Flat-footed] against any creature to which you do not have line of sight, and are not automatically aware of the square or squares it occupies, or even the direction to it. You can attempt to attack a creature you do not have line of sight to in a square you believe it occupies. If the creature is there, you attack them as normal. If the creature isn’t there, then your attack does nothing.
Line of Effect
A line of effect is a straight, unblocked line between two squares or a grid intersection and a square that indicates what an ability or attack can target or affect.
A line of effect is canceled by any solid barrier that would normally be sufficient to block movement without a special movement mode, and by certain abilities that specifically block line of effect. You can establish line of effect even without line of sight, and in some cases it may be possible to have line of sight without line of effect. For example, a sphere of darkness or a paper screen would block line of sight but not line of effect, while a cage of unbreakable glass or wall of invisible force would block line of effect but not line of sight.
You must have a clear line of effect to any target you attack, or against which you attempt to activate an ability, or to any space in which you wish to create an effect. You must have a clear line of effect to the point of origin of any ability you activate. If you somehow occupy the interior of an object or terrain feature that would block line of effect, it blocks your line of effect.
An area effect affects only an area, creatures, or objects to which it has line of effect from its origin.
An otherwise solid barrier with a hole of at least 1 square foot through it only blocks line of effect for melee attacks. It is not treated as a barrier for any other attack or ability.
Whenever a creature or object moves 5 ft or more within the range of your [Ghostwise sight], it becomes visible to you as a trailing phantasm, allowing you to see where it moves, until the end of that movement, even if it moves via a [Teleport] effect. If they are [Invisible], your perception is blurred, but not completely fooled, and you ignore the normal effects of [Invisible], but treat the target as [Concealed] for purposes of aiming and other interactions. Interestingly, this means that even if it would be hidden by a wall, you can see it as though it had no cover. Unfortunately, the wall will still stop an arrow. A successful Stealth check against your Awareness defense reduces this to a general directional awareness of the creature which made the Stealth check.
Tremorsense functions like [Ghostwise sight], but it ignores the [Invisible] condition entirely. Further, as a swift action, you can image the area, locating stationary objects and creatures. This allows you to make a Perception check (DC 10 + creature's total Stealth modifier) to detect each creature in the area using the Stealth skill, and also allows you to automatically detect any creatures in the area to which you do not have Line of Sight and which are not using the Stealth skill, and discern the features of terrain in the area that you could not otherwise perceive with normal vision or other special vision modes.
You have sight beyond sight, but only a little beyond. You can see in the dark, allowing you to ignore difficulties of poor illumination. Additionally, magical darkness generated by any effect of fourth circle or lower is reduced to an uneven shadowing of your vision, allowing you to ignore its effects.
[Blindsight] functions as if it were [Darkvision] within its limited range, but ignore magical darkness of 6th circle or lower, and ignores [Concealed], [Fully concealed], the [Invisible] condition, and Stealth bonuses from clouds, smoke, and other forms of concealment that rely on eliminating visual cues.