The box within a box solution above is a good option, but if that won't work (due to variably sized/shaped objects) you might be able to accomplish something with Physics.Raycast or Collider.Raycast. I had a similar problem where I needed to test if arbitrary points were contained inside colliders (many of which were unusual blobby concave objects).
The basic idea is a "bed of nails" approach where I cast rays toward the point from multiple directions. If I hit the outside collider on all of the rays, then I can be pretty confident that the point is contained inside the collider (but still not completely certain). Here's a pic:
In this picture, we're trying to see if the blue point is inside the yellow collider. The GREEN arrows represent successful raycasts (the yellow collider is hit), and the PINK one is unsuccessful (the yellow collider is NOT hit).
Here is a code snippet illustrating this:
public static class CollisionUtils {
private static readonly Vector3[] raycastDirections;
// These are the directions that we shoot rays from to check the collider.
static UltrasoundCollisionUtils() {
raycastDirections = new Vector3[5];
raycastDirections[0] = new Vector3(0,1,0);
raycastDirections[1] = new Vector3(0,-1,-0);
raycastDirections[2] = new Vector3(0,0,1);
raycastDirections[3] = new Vector3(-1.41f, 0, -0.5f);
raycastDirections[4] = new Vector3(1.41f, 0, -0.5f);
}
public static bool IsContained (Vector3 targetPoint, Collider collider) {
// A quick check - if the bounds doesn't contain targetPoint, then it definitely can't be contained in the collider
if (!collider.bounds.Contains(targetPoint)) {
return false;
}
// The "100f * direction" is a magic number so that we
// start far enough from the point.
foreach (Vector3 direction in raycastDirections) {
Ray ray = new Ray(targetPoint - 100f * direction, direction);
RaycastHit dummyHit = new RaycastHit();
// dummyHit because collider.Raycast requires a RaycastHit
if (!collider.Raycast(ray, out dummyHit, 100f)) {
return false;
}
}
return true;
}
}
One way you could adapt this algorithm is rather than use Collider.Raycast, do a Physics.Raycast. If the rays hit anything other than your collider, then you know that your target object isn't entirely in the collider.
