How to check that object not hidden by another object? - unity3d

Question

I make game with isometric view. When player comes into the house the roof of it hides and player can interact with NPCs, items, etc. But now it can interact with it even when roof is visible. How to detect that item is hidden by house roof or wall or another object?
void Update() {
Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
RaycastHit[] hits = Physics.RaycastAll(ray, Mathf.Infinity);
if (Input.GetMouseButtonDown(0)) {
foreach (RaycastHit hit in hits) {
if (hit.collider.tag != "NPC") {
continue;
}
//Interact ...
}
}
}

Answer 1

You can simply check the distance between the hit wall/roof and NPC, from the ray-cast origin (camera). Like so:
private Camera cameraRef;
private void Awake() {
// P.S: Cache the 'Camera.main', calls to it can be expensive.
cameraRef = Camera.main;
}
void Update() {
if (Input.GetMouseButtonDown(0)) {
Ray ray = cameraRef.ScreenPointToRay(Input.mousePosition);
RaycastHit[] hits = Physics.RaycastAll(ray, Mathf.Infinity);
foreach (RaycastHit hit in hits) {
if (hit.collider.tag != "NPC") {
continue;
} else if (RaycastHitRoofOrWallFirst(hits, hit.collider.gameObject)) {
// This NPC is hidden behind a roof/wall.
continue;
}
// Interaction...
}
}
}
/// <summary>
/// Check if a target object is being hidden behind a roof/wall.
/// </summary>
/// <param name="hits">The hits that the raycast gotten.</param>
/// <param name="targetObject">The gameobject to check against.</param>
/// <returns>Return true if the target object is hidden, false if not.</returns>
private bool RaycastHitRoofOrWallFirst(RaycastHit[] hits, GameObject targetObject) {
foreach (RaycastHit hit in hits) {
if (hit.collider.CompareTag("roof") || hit.collider.CompareTag("wall")) {
float distanceFromCameraToObstacle = Vector3.Distance(cameraRef.transform.position, hit.collider.transform.position);
float distanceFromCameraToNPC = Vector3.Distance(cameraRef.transform.position, targetObject.transform.position);
// Check if the NPC is closer to the camera (raycast origin)
// compared to the roof or wall.
if (distanceFromCameraToObstacle < distanceFromCameraToNPC) {
// The roof/wall is closer to the camera (raycast origin)
// compared to the NPC, hence the NPC is blocked by the roof/wall
return true;
}
}
}
return false;
}
Here is a small visual diagram of what it should check for:
Or just use simple raycast...
If possible depending on the context, instead of using Physics.RaycastAll, you can use Physics.Raycast.
It returns the first object that the ray-cast hits.

Answer 2

Adding to this answer an alternative could maybe also be using OnBecameVisible
OnBecameVisible is called when the object became visible by any Camera.
This message is sent to all scripts attached to the Renderer.
and OnBecameInvisible
OnBecameInvisible is called when the Renderer is no longer visible by any Camera.
This message is sent to all scripts attached to the Renderer.
OnBecameVisible and OnBecameInvisible are useful to avoid computations that are only necessary when the object is visible.
For activating and deactivating the according NPC's colliders so the Raycast anyway will only work on visible objects in the first place.
Like on the NPCs have a script
public class InteractableController : MonoBehaviour
{
// you can also reference them via the Inspector
public Collider[] colliders;
private void Awake()
{
// pass in true to also get inactive components
if(colliders.Length = 0) colliders = GetComponentsInChildren<Collider>(true);
}
private void OnBecameInvisible()
{
foreach(var collider in colliders)
{
collider.enabled = false;
}
}
private void OnBecameVisible()
{
foreach(var collider in colliders)
{
collider.enabled = true;
}
}
}
However
Note that object is considered visible when it needs to be rendered in the Scene. It might not be actually visible by any camera, but still need to be rendered for shadows for example. Also, when running in the editor, the Scene view cameras will also cause this function to be called.