5.10 Obstacles and Cover
In a battle, you may not be able to perfectly see all of your opponents. When obstacles get in the way, they may make some attacks impossible. Almost all abilities, including strikes, must have line of sight and line of effect. Smaller obstacles may simply provide cover instead of making attacks impossible. This section explains how to deal with obstacles and related limitations.
5.10.1 Point of Origin
When you make an attack, you have to determine the point of origin. For targeted attacks, which are the most common, the point of origin is a grid intersection of your choice that is touching your space. For area attacks, the point of origin depends on the shape of the area and whether it has a defined range.
If an area attack has a defined range, the point of origin is a single grid intersection of your choice within that range. Cones, lines, and walls without a range use a grid intersection of your choice that is touching your space, just like targeted attacks. Cylinders and spheres without a range are unusual, since they radiate from your whole body instead of a single point. When determining their total size, treat every grid intersection touching your space as a point of origin. When determining cover and similar effects, only use the grid intersection that is closest to the target.
5.10.2 Cover
Cover represents any obstacle that physically prevents you from striking your target, such as a tree or intervening creature. A creature or object behind cover gains a +2 bonus to Armor and Reflex defenses. If an attack would miss or glance the defense of a creature or object behind cover, the attack is instead applied to the obstacle instead of to the intended target. In the case of area attacks, this cannot cause an individual creature or object to be targeted or attacked twice by the same ability. This can protect creatures behind cover from attacks that deal damage on a miss (see Glancing Blows). In addition, a creature behind cover can hide (see Stealth).
Cover is only relevant if the attacker has line of effect to its target (see Line of Effect). If you don’t have line of effect, you generally can’t attack the target at all, so the defense bonuses from cover don’t matter.
Measuring Cover
To measure cover for a particular attack, draw a cone from the attack’s point of origin to the two closest corners of the target’s space. For creatures that occupy multiple 5 ft. squares, that these must be corners where the target’s space ends, not just grid intersections touching squares the target occupies. The defender can choose between equally distant corners. If there are any obstacles in that cone, the target has cover.
Your allies do not provide cover for attacks you make, as long as you are able to see or hear each other to coordinate. In addition, obstacles only provide cover if the relevant part of the obstacle is no more than one size category smaller than the target. You should ignore any irrelevant parts of the obstacle that are outside of the cone. For example, although a tree might be Gargantuan or Colossal if you include all of its leaves and branches, most trees are only a Medium size obstacle at ground level, since only their trunk is relevant. The rules typically ignore the complexity of three-dimensional space, so you’ll have to estimate what would provide reasonable cover in some cases.
Improved Cover
Cover of the same type generally doesn’t stack; a creature behind two trees is not substantially more protected than a creature behind a single tree. However, exceptionally well covered creatures, such as a creature behind an arrow slit in a castle, may gain a +4 benefit to Armor and Reflex defenses rather than the normal +2 at the GM’s discretion.
5.10.3 Line of Sight
Unless otherwise noted in an ability’s description, you cannot target a creature, object, or location that you do not have line of sight to. Line of sight measures whether you can see things, not whether you can touch or reach them.
A line of sight is a straight, unblocked path between an attacker and a target. To measure line of sight for a particular attack, draw a line between any grid intersection touching your space and any grid intersection touching the target’s space. If you’re targeting a particular point, you would naturally draw the line to that point instead. If this line is not blocked by any obstacles that impede sight, you have line of sight to your target.
5.10.4 Line of Effect
Almost all abilities, including strikes, must have a line of effect to function. Line of effect measures whether physical passage is possible between two locations, regardless of any sight obstacles. For example, a pane of glass would block line of effect, but not line of sight.
Unless otherwise noted in an ability’s description, you cannot target a creature, object, or location that you do not have line of effect to. In addition, abilities that affect an area do not affect targets that the ability does not have line of effect to.
A line of effect is a straight, unblocked path between an attacker and a target. To measure line of sight for a particular attack, draw a line between the attack’s point of origin and any grid intersection touching the target’s space. If you’re targeting a particular point, you would naturally draw the line to that point instead. If this line is not blocked by any obstacles that make physical passage impossible, you have line of effect to your target.
Destroying Barriers
Some abilities deal damage to both creatures and objects. If a physical barrier is broken by an ability, that barrier does not affect the ability’s line of effect. For example, a thin curtain of silk normally blocks line of effect. However, an ability that destroyed the curtain would have its full effect on everything behind the curtain.
Inside Creatures
Creatures block line of effect to the inside of their own bodies. As a result, you cannot use an ability that takes effect inside a creature unless you are also inside the creature. This restriction applies even if there is no physical barrier to the inside of the creature. For example, you cannot place the point of origin for an area inside a creature’s mouth, even if the creature has its mouth open at the time.