Enemy AI in stealth games can be tricky to get right. Enemies need to appear smart and responsive, yet be predictable enough that the player can form and execute a plan to avoid or escape them.

One of the best tricks to make enemy AI look smart is to make the character say something relevant to the situation. For example, if two agents engage in a brief call-and-response while searching for a target, many players will believe the AI is sharing knowledge between the two agents, regardless of whether it actually is.

In NEON STRUCT, I’m working without that particular secret weapon. For scope, budget, and tone reasons, I’ve chosen to forgo voice acting, so I’ve had to find other ways to indicate AI state. The quintessential example of a voiceless AI indicator is Metal Gear Solid‘s exclamation point, so I’m starting there. Enemies in NEON STRUCT have multiple awareness states, so each one has a different icon (and associated audio tone).

These states reflect the AI’s awareness of the player or other targets, and also correspond directly to the enemy’s behavior. The “…” means the AI has only limited awareness. It corresponds to the Notice behavior, which makes the enemy pause momentarily to look in the direction of the disturbance.

The “?” means the AI has increased awareness of the target, but not enough awareness to engage with a threat. For example, the AI may have heard loud footsteps or seen a dead body, but not yet found the actual target. This corresponds to the Search behavior, in which the enemy cautiously investigates the disturbance.

Finally, the “!” means the AI has enough visual awareness of the target to identify it as a threat. That corresponds to the Combat behavior, which is relatively simple because the player has no weapon of her own. Combative enemies chase the target to melee distance while firing a ranged weapon if available.

Awareness is a complex system that combines multiple fuzzy inputs (sight and hearing at various distances, illumination levels, etc.) into a discrete number of states. Determining the appropriate thresholds at which to switch between states is part of the secret sauce of stealth AI, and one of the factors which will be undergoing continuous evaluation and iteration during playtesting.