ColliderExtensions for checking overlapping colliders without using Unity physics.

ColliderExtensions.cs

using UnityEngine;
using System.Collections;

public static class ColliderExtensions
{
	public static bool Overlaps (this BoxCollider box, SphereCollider sphere)
	{
		//Im sure there is a better way to do this, but it works for now.

		var sphereWorldCenter = sphere.transform.TransformPoint (sphere.center);
		var sphereWorldRadius = new Vector3 (sphere.transform.lossyScale.x * sphere.radius, 0, 0);

		//
		// Reset box to worldspace scale (1,1,1)
		//
		var originalBoxCenter = box.center;
		var originalBoxSize = box.size;
		var originalBoxScale = box.transform.localScale;
		box.center = Vector3.Scale (box.center, box.transform.lossyScale);
		box.size = Vector3.Scale (box.size, box.transform.lossyScale);
		box.transform.SetGlobalScale (Vector3.one);


		var sphereCenterInBoxSpace = box.transform.InverseTransformPoint (sphereWorldCenter) - box.center;
		var s = box.transform.InverseTransformVector (sphereWorldRadius).magnitude;
		float sphereRadiusInBoxSpace = s;
		var extents = box.size / 2;

		Vector3 distanceFromCenterOfBox = new Vector3 (Mathf.Abs (sphereCenterInBoxSpace.x), Mathf.Abs (sphereCenterInBoxSpace.y), Mathf.Abs (sphereCenterInBoxSpace.z));

		bool result = false;

		//float sphereRadiusInBoxSpace = Mathf.Max (Mathf.Max (s.x, s.y), s.z);

		if (distanceFromCenterOfBox.x > sphereRadiusInBoxSpace + extents.x)
			goto defer;
		if (distanceFromCenterOfBox.z > sphereRadiusInBoxSpace + extents.z)
			goto defer;
		if (distanceFromCenterOfBox.y > sphereRadiusInBoxSpace + extents.y)
			goto defer;

		if (distanceFromCenterOfBox.x <= extents.x && distanceFromCenterOfBox.z <= extents.z && distanceFromCenterOfBox.y <= extents.y) {
			result = true;
			goto defer;
		}

		Vector3 closestPointOnBox = new Vector3 (Mathf.Clamp (sphereCenterInBoxSpace.x, -extents.x, extents.x),
			Mathf.Clamp (sphereCenterInBoxSpace.y, -extents.y, extents.y),
			Mathf.Clamp (sphereCenterInBoxSpace.z, -extents.z, extents.z));

		var distVector = closestPointOnBox - sphereCenterInBoxSpace;

		result = (distVector.sqrMagnitude < sphereRadiusInBoxSpace * sphereRadiusInBoxSpace);

		defer:

		//Restore box scale
		box.center = originalBoxCenter;
		box.size = originalBoxSize;
		box.transform.localScale = originalBoxScale;

		return result;
	}

	public static bool Overlaps (this SphereCollider sphere, BoxCollider box)
	{
		return box.Overlaps (sphere);
	}

	public static bool OverlapsDebug (this BoxCollider box, SphereCollider sphere, out Vector3 spherePos, out float sphereRadius)
	{
		//Im sure there is a better way to do this, but it works for now.

		var sphereWorldCenter = sphere.transform.TransformPoint (sphere.center);
		var sphereWorldRadius = new Vector3 (sphere.transform.lossyScale.x * sphere.radius, 0, 0);

		//
		// Reset box to worldspace scale (1,1,1)
		//
		var originalBoxCenter = box.center;
		var originalBoxSize = box.size;
		var originalBoxScale = box.transform.localScale;
		box.center = Vector3.Scale (box.center, box.transform.lossyScale);
		box.size = Vector3.Scale (box.size, box.transform.lossyScale);
		box.transform.SetGlobalScale (Vector3.one);


		var sphereCenterInBoxSpace = box.transform.InverseTransformPoint (sphereWorldCenter) - box.center;
		var s = box.transform.InverseTransformVector (sphereWorldRadius).magnitude;
		float sphereRadiusInBoxSpace = s;
		var extents = box.size / 2;

		Vector3 distanceFromCenterOfBox = new Vector3 (Mathf.Abs (sphereCenterInBoxSpace.x), Mathf.Abs (sphereCenterInBoxSpace.y), Mathf.Abs (sphereCenterInBoxSpace.z));

		bool result = false;

		//float sphereRadiusInBoxSpace = Mathf.Max (Mathf.Max (s.x, s.y), s.z);

		if (distanceFromCenterOfBox.x > sphereRadiusInBoxSpace + extents.x)
			goto defer;
		if (distanceFromCenterOfBox.z > sphereRadiusInBoxSpace + extents.z)
			goto defer;
		if (distanceFromCenterOfBox.y > sphereRadiusInBoxSpace + extents.y)
			goto defer;

		if (distanceFromCenterOfBox.x <= extents.x && distanceFromCenterOfBox.z <= extents.z && distanceFromCenterOfBox.y <= extents.y) {
			result = true;
			goto defer;
		}

		Vector3 closestPointOnBox = new Vector3 (Mathf.Clamp (sphereCenterInBoxSpace.x, -extents.x, extents.x),
			                            Mathf.Clamp (sphereCenterInBoxSpace.y, -extents.y, extents.y),
			                            Mathf.Clamp (sphereCenterInBoxSpace.z, -extents.z, extents.z));

		var distVector = closestPointOnBox - sphereCenterInBoxSpace;

		result = (distVector.sqrMagnitude < sphereRadiusInBoxSpace * sphereRadiusInBoxSpace);

		defer:

		spherePos = box.transform.TransformPoint (sphereCenterInBoxSpace);
		var s2 = box.transform.TransformVector (new Vector3 (sphereRadiusInBoxSpace, 0, 0));
		sphereRadius = s2.magnitude;

		//Restore box transforms
		box.center = originalBoxCenter;
		box.size = originalBoxSize;
		box.transform.localScale = originalBoxScale;

		return result;
	}

	public static void SetGlobalScale (this Transform transform, Vector3 globalScale)
	{
		transform.localScale = Vector3.one;
		var lossyScale = transform.lossyScale;
		transform.localScale = new Vector3 (globalScale.x / lossyScale.x, globalScale.y / lossyScale.y, globalScale.z / lossyScale.z);
	}

	public static bool OverlapsDebug (this SphereCollider sphere, BoxCollider box, out Vector3 spherePos, out float sphereRadius)
	{
		return box.OverlapsDebug (sphere, out spherePos, out sphereRadius);
	}
}