Sight mechanics

Sight or Vision in Baldur's Gate 3 is governed by a combination of physical lines of sight, environmental lighting (obscurity), and specific surface/area properties. These interacting systems dictate whether a creature can be targeted, whether an attack receives a bonus or a penalty, and whether a character can successfully hide.

Overview

Line of sight

A line of sight is needed to spot a sneaking character, and use ranged "target" abilities on a target or a ground position. When there is no line of sight, these actions or spells cannot be used. A line of sight can blocked by terrain, objects, and clouds such as  Fog and  Darkness.

Line of sight and obscuration

Understanding how the game engine processes vision requires knowing its distinction between total concealment and obscuration:

• Total Concealment occurs when a physical object or specific magical area ends or otherwise interrupts the line of sight between a source and the target of its observation. Total Concealment can be caused by obstacles such as walls, closed doors, trees and large rocks.
• Obscuration is a measure of brightness with three stages:  Clear,  Lightly Obscured, and  Heavily Obscured. It is caused by naturally dark areas, clouds and fog, and areas of certain spells (e.g.,  Hunger of Hadar). Many creatures have a basic 2m (7ft) of  Darkvision, which reduces obscuration by 1 level for the viewer. Attack rolls have  Disadvantage against a  Heavily Obscured target ("too dark"), and  Advantage when the attacker is heavily obscured from the perspective of their target ("attacking from shadows").

Target actions and Projectile actions

Line of sight check is integral for character actions. The game engine divides ranged abilities into "target actions" and "projectile actions."

• A ranged target action targets a creature or a place on the ground, requires Line of sight to the target, and does not use a projectile. Examples include  Sacred Flame,  Sleep,  Shatter, and  Misty Step. These abilities commonly, though not always, use a saving throw and / or attack roll. For example,  Bone Chill is a target action with an attack roll.
• A projectile action involves transit of a projectile - which can be identified by a trajectory line or arc reaching to the target when aiming the ability. Examples include ranged weapon attacks and spells like  Fire Bolt,  Fireball, and  Magic Missile. They do not specifically require sight, but do require an unobstructed physical path. This distinction becomes relevant when interacting with artificial clouds. Although not required, these actions commonly use attack rolls, in which case they are affected by obscuration.  Magic Missile and  Fireball are examples of projectile-like spells which have no attack rolls.

Cloud interactions with Line of sight

In addition to landscape features and objects, clouds created by spells or other features can also block line-of-sight and projectile paths.

•  Fog clouds block vision, preventing the use of targeting actions through or into them, and also cut off creature vision cones, preventing them from spotting sneaking characters. Fog clouds do not affect projectile actions, They do create  Heavy Obscuration within their area, though this does not affect creatures outside of the cloud that are merely seen through the cloud (unlike Line of sight). Because line of sight and obscuration systems are not connected, obscuration from fog clouds can be negated by  Darkvision, even when creatures with Darkvision cannot 'see' through the cloud. Additionally, these mechanics allow creatures with Darkvision to make ranged attacks at targets in clouds without disadvantage, and also allow creatures with Darkvision to negate the advantage a creature would normally get by firing from obscuration created by a cloud.
• Clouds like  Cloudkill and  Stinking Cloud provide obscuration only, and do not block 'sight', leaving Target actions unaffected.
•  darkness clouds create a stricter impediment, while they block vision and create obscuration as Fog clouds do, they also block projectiles completely – although objects can move through them otherwise. The sight and projectile blocking behaviour of darkness clouds prevents ranged actions into or through them, except for creature immune to them via features like  Devil's Sight or the  Eversight Ring. Ordinary  Darkvision is not sufficient to help creatures attacking into or through Darkness clouds, as they cannot make attacks into them to begin with, although Darkvision should still enable them to prevent creatures in darkness clouds from gaining advantage when attacking them due to being in a  Heavily Obscured location.

The IgnoreSurfaceCover Bug

• There is a known bug regarding the IgnoreSurfaceCover internal boost which manifests with Fog. Specifically, if a surface has the property CanSeeThrough = false but CanShootThrough = true (like  Fog Cloud), any active IgnoreSurfaceCover boost allows a creature to see through it. Conversely, if CanShootThrough = false (like  Darkness), the creature must have the specific IgnoreSurfaceCover(SurfaceDarknessCloud) boost to see through it. The result is that features which grant sight through Magical Darkness (e.g.,  Devil's Sight) implicitly grant sight through Fog, but Fog-specific protections do not work against Darkness. A primary example of this interaction is the  Fog cloud. Notably, this bug does not extend to clouds that block both vision and projectiles, such as  Magical Darkness, where the CanShootThrough = false parameter prevents the exploit.
• Darkness Immunity and Fog Interaction: Creatures possessing immunity to Darkness clouds – typically through features like  Devil's Sight or  Born into Darkness – unintentionally gain the ability to 'see' through Fog clouds. This allows them to use targeted spells and abilities that would normally be obstructed.
  • It is important to note that this interaction does not modify underlying obscuration rules. Visibility remains dependent on Darkvision. While some features that grant Darkness immunity also provide Darkvision, others do not; therefore, a creature might be able to target through the Fog but still suffer penalties if they lack the appropriate vision type to resolve the obscuration.

Creature Sight and Behavior Mechanics

Creature behavior regarding player character sightlines is determined by a combination of vision cones, obscuration, total concealment, and "functional invisibility" (a state achieved by successfully  Hiding or gaining the  Invisible condition). While out-of-combat behavior primarily dictates stealth attack logic, in-combat creature behaviour is based on three primary visibility states:

1. Direct Line of Sight – When a creature has an unobstructed view of a player character, it engages using its standard NPC opponent routines.

2. Potential Line of Sight (obstructed or hidden) – This state occurs when a party member is in the environment but not immediately targetable. The creature's response depends on the nature of the obstruction:

• Physical Cover: If line of sight is blocked by objects resulting in total concealment, the creature will attempt to move into a position to restore visibility or use abilities that do not require line-of-sight.
• Cloud Effects: NPC opponent behaviour diverges depending on the cloud type. Because Fog allows projectiles, creatures will typically fire ranged attacks into it or walk inside to use standard abilities. Conversely,  Magical Darkness blocks projectiles, which discourages creatures from entering. They will prioritize throwing items from the outside, or simply end their turn if they cannot find a valid action.
• Active Stealth: When a player character attempts to hide within an obscured area (or a creature's potential detection range), it triggers a passive Perception check against the player character's Stealth. If the creature fails this check, or if the player character is actively  Invisible, the opponent's logic will attempt to move its vision cone over the player's character's last known location.
• Sense Hidden Presence: If moving the vision cone fails to reveal the party member, the creature will attempt to use the  Sense Hidden Presence action within 3 meters of their last known location. However, a known limitation exists with opponent "pathing logic": if the creature cannot reach its intended location and use its intended ability in the same turn, often due to insufficient movement speed or the requirement to use a  Jump action, it will not advance to prepare for its next turn and instead do nothing.

3. No Line of Sight (functionally invisible) – When a player character is functionally invisible and entirely outside of a creature's potential line of sight, such as hiding within a Fog cloud when the creature lacks Devil's Sight, the creature recognizes no actionable targets.

Consequently, combining this state with the opponent pathing limitations of Sense Hidden Presence allows party members to reliably force enemy units to skip their turns by consistently hiding out of their functional range.