Simple Stealth AI: Believable Immersion Without Complex Overhauls

Forget complex AI overhauls. The key to a believable stealth experience isn’t about crafting sentient digital beings, but about cleverly exploiting simple, yet effective techniques. We’re going to construct a stealth system that’s surprisingly robust, focusing on core mechanics that sell the illusion of intelligence. This isn’t just about avoiding detection; it’s about making the act of detection feel meaningful and reactive.

The All-Seeing Eye: Vision Cone with Raycasting

A guard’s vision isn’t an omniscient radar. It’s limited, directional, and can be fooled. Raycasting is our tool to mimic this effectively.

Instead of simply checking the distance to the player, we’ll fire multiple raycasts outwards in a fan shape, creating our vision cone.

Here’s the critical part: the density of the raycasts matters. More rays mean more accurate detection, but also higher computational cost. A good starting point is 15-20 rays, adjusting based on performance.

Pitfall alert: Ensure your raycasts ignore the guard’s own collider! Nothing’s more immersion-breaking than a guard instantly “seeing” itself.

// Example (Conceptual - adapt to your engine)
for (int i = 0; i < numberOfRays; i++) {
    float angle = transform.eulerAngles.y - fieldOfView / 2 + fieldOfView / numberOfRays * i;
    Vector3 direction = Quaternion.Euler(0, angle, 0) * Vector3.forward;
    Ray ray = new Ray(transform.position, direction);
    RaycastHit hit;

    if (Physics.Raycast(ray, out hit, viewDistance)) {
        if (hit.collider.CompareTag("Player")) {
            // Player detected!
            Debug.Log("Player Spotted!");
        }
    }
}

Beyond basic detection, consider adding these enhancements:

• Obstructed Vision: Raycasts should check for obstacles. If a ray hits a wall before the player, the player is hidden.
• Partial Visibility: If only some rays hit the player, the guard becomes “suspicious” instead of immediately alerted.

Hear a Pin Drop: Sound-Based Detection

Stealth isn’t just about sight; sound plays a vital role. We’ll create a system where player actions generate noise, alerting nearby guards.

First, define “sound events.” These could be footsteps, opening doors, or breaking objects. Each event should have a defined radius of audibility.

When the player performs a sound event, broadcast a “sound signal” with its origin and radius.

Guards within range of the signal should then investigate the source.

Here’s a crucial detail: avoid a simple distance check. Factor in obstacles! A sound may be loud, but a thick wall should muffle it significantly. Raycasting again provides the solution – check for obstructions between the sound source and the guard.

Example:

//Player Script
public void MakeFootstepSound(){
    //Broadcast sound event with location
    SoundManager.instance.BroadcastSound(transform.position, footstepRadius);
}

//SoundManager Script
public void BroadcastSound(Vector3 position, float radius) {
    foreach (GuardAI guard in FindObjectsOfType<GuardAI>()) {
        float distance = Vector3.Distance(position, guard.transform.position);
        if (distance <= radius) {
            // Check if there's a clear path to the sound source.
            RaycastHit hit;
            if(Physics.Raycast(position, (guard.transform.position - position).normalized, out hit, radius)) {
                if (hit.collider.GetComponent<GuardAI>() == null && hit.collider.GetComponent<PlayerController>() == null)
                {
                   //Obstacle in the way, reduce sound intensity.
                   //Don't alert the Guard, if the reduction is too high.
                   //(Implementation Details)
                } else {
                    guard.Investigate(position);
                }
            }

        }
    }
}

//GuardAI Script
public void Investigate(Vector3 soundPosition) {
    //Set destination, to the soundPosition
    agent.SetDestination(soundPosition);
    //Enter investigation state.
}

The Thinking Machine: Basic AI Awareness

A truly compelling stealth system requires the AI to remember and react to its environment. We need to give our guards a basic “memory.”

Implement a simple “suspicion” system. When a guard detects something unusual (a sound, a glimpse of the player), it enters a “suspicious” state.

In this state, the guard should:

• Investigate the last known location of the disturbance.
• Increase its alertness level (e.g., wider vision cone, faster reaction time).
• Remember the disturbance for a short period. If the player isn’t found, the guard eventually returns to its normal patrol.

The critical mistake here is forgetting too quickly. A guard who immediately dismisses a loud noise seems oblivious, not intelligent. Implement a short “cooldown” period after an investigation, during which the guard remains vigilant.

Furthermore, implement a patrol system using waypoints. The guard should seamlessly transition between investigating disturbances and following its patrol route. This adds a layer of realism and prevents the AI from getting stuck or behaving predictably.

Level Design is Key

No AI system can compensate for poor level design. Open, featureless environments make stealth trivial.

• Verticality: Multiple levels create opportunities for both evasion and ambushes.
• Cover: Provide ample cover – crates, pillars, walls – to break line of sight.
• Chokepoints: Force the player to make risky decisions by creating narrow passages guarded by enemies.

Putting it all Together

Integrating these elements creates a surprisingly compelling stealth experience. The guard’s vision cone, combined with sound-based detection and a basic awareness system, forces the player to think carefully about their actions. By focusing on believable reactions rather than complex AI, you can achieve a level of immersion that rivals far more sophisticated systems. Remember, it’s the illusion of intelligence that truly matters.