Mobile VR Gaze Interface: Raycast, Dwell, Reticle Implementation

Mobile VR without controllers — the only interaction method is gaze direction. It seems simple: look at a button and it clicks. In practice, poorly implemented gaze annoys users faster than any other UI pattern. Over the years, we have developed a stack and approaches that guarantee comfortable interaction. Our experience: 5+ years in mobile VR development, over 20 projects with gaze interface. We offer a turnkey solution: from raycast to progress indicator. We implement the basic system in 3–5 days, full system in 1–2 weeks. According to Google Cardboard documentation, gaze-based interaction is the standard input method for mobile VR without controllers.

How does raycast from the gaze center work?

Gaze is determined by the camera's view direction. The ray is cast from the camera position forward along Camera.main.transform.forward:

void FixedUpdate() { Ray gazeRay = new Ray(Camera.main.transform.position, Camera.main.transform.forward); if (Physics.Raycast(gazeRay, out RaycastHit hit, maxGazeDistance, interactableLayer)) { var target = hit.collider.GetComponent<IGazeTarget>(); if (target != null) { HandleGazeHit(target, hit.point); } else { HandleGazeMiss(); } } else { HandleGazeMiss(); } } 

FixedUpdate() instead of Update() — stable call frequency not tied to FPS. On weak devices with drops to 30 FPS, Update() gives uneven response. The interactableLayer is mandatory: raycasting across the entire scene is expensive, and the user should not accidentally activate invisible colliders.

How to implement reticle (gaze cursor)?

Reticle is a visual indicator of the gaze point. It is placed in world space on the surface of the object under gaze. Distance is dynamic: the reticle "sticks" to the hit point.

void UpdateReticle(Vector3 hitPoint, Vector3 hitNormal) { reticleTransform.position = hitPoint + hitNormal * RETICLE_OFFSET; reticleTransform.rotation = Quaternion.LookRotation(-hitNormal); // Constant apparent size in angular units float dist = Vector3.Distance(Camera.main.transform.position, hitPoint); reticleTransform.localScale = Vector3.one * dist * ANGULAR_SIZE; } 

Note: when no object is under gaze — reticle at default distance (3–5 meters). We don't hide it: the user should always see where they are looking.

Dwell activation and progress indicator

The user looks at an object for N seconds — activation occurs. Optimal dwell time: 1.2–2.0 seconds. Less than 1 second leads to accidental activations when scanning the scene, more than 2 seconds fatigues. Progress must be noticeable. A filling ring around the reticle is standard:

public class GazeDwellController : MonoBehaviour { [SerializeField] private float dwellTime = 1.5f; [SerializeField] private Image progressRing; private float dwellProgress = 0f; private IGazeTarget currentTarget; private bool isActivated = false; public void OnGazeEnter(IGazeTarget target) { currentTarget = target; dwellProgress = 0f; isActivated = false; progressRing.gameObject.SetActive(true); } public void OnGazeStay() { if (isActivated) return; dwellProgress += Time.deltaTime / dwellTime; progressRing.fillAmount = dwellProgress; if (dwellProgress >= 1f) { isActivated = true; currentTarget?.OnGazeActivate(); StartCoroutine(ResetAfterDelay(0.5f)); } } public void OnGazeExit() { currentTarget = null; progressRing.gameObject.SetActive(false); dwellProgress = 0f; } } 

After activation — a short cooldown before the next activation of the same object (0.5–1.0 sec). Otherwise the user cannot remove their gaze in time and the button "clicks" twice.

Hover state: feedback before activation

Note: when the user looks at an object but dwell is not yet complete, immediate visual feedback is needed. The object should react at OnGazeEnter — before the activation time elapses. Options:

• Highlight: change material emission color
• Scale: object slightly enlarges (0.05f is enough)
• Animation: icon responds to gaze
• Sound: short click when dwell starts

Without this, the user doesn't know if the application "sees" them.

Cardboard button as confirmation

The Cardboard has a physical button (magnetic trigger). We add it as an alternative activation method instead of dwell — for advanced users it is faster and more convenient:

// Cardboard SDK trigger event void Update() { if (CardboardInput.GetButtonDown()) { TriggerCurrentGazeTarget(); } } 

The button is not a replacement for dwell, but a supplement. Not all Cardboard cases have a working magnetic button.

What typical errors occur with gaze interaction?

Too small collider on interactive object — user "misses" the button. The collider should be 10–20% larger than the visible object. Gaze speed (angular velocity) affects accuracy: during rapid scanning, a speed threshold resets dwell. Reticle jitters due to gyroscope — Lerp with 20 ms time eliminates jitter. Use a separate layer for raycast to avoid accidental activations and save performance.

Comparison of activation methods

What's included in the work

• Documentation of gaze system architecture
• Source code: raycast, reticle, dwell controller, hover state
• Integration with Cardboard SDK and alternative triggers
• Testing on devices (iOS/Android) with different Cardboard versions
• Support for 2 weeks after delivery

Process of work

1. Analysis of interactive elements: object types, interaction scenarios.
2. Implement raycast system with proper layers and colliders.
3. Reticle in world space with constant apparent size.
4. Dwell controller with progress indicator, hover state, cooldown.
5. Cardboard button as alternative trigger.
6. Comfort testing: dwell time, button sizes, feedback.

Timeline estimates

Basic gaze interaction system with reticle and dwell — 3–5 days. Full-fledged system with multiple types of interactive objects, animations, sound, and configurable parameters — 1–2 weeks.

We guarantee comfortable interaction. Certified Unity and Android/iOS developers. Contact us to discuss your project — we will implement a gaze interface for your mobile VR application.