How can I detect which SIDE of a box I collided with?

INFO… I am using an empty with 4 cubes (That have Ridgedbodys & Box colliders and using the “function OntriggerEnter”) to make up my gameobject “BLOCk”. My BLOCK will be my player and drop to the floor(A Plane) slowly, if it hits the floor or the top of another BLOCK it will kill the movement script and create another BLOCK to control at the top.

Question… I want to DoSomething if I hit the “TOP” of a different BLOCK but DoSomething else if I hit the “SIDE” of that BLOCK.

I would like to keep it simple and not use a char controller, but from what I am reading that might not be an option. I was thinking of using a raycast maybe.

I am using this right now for my floor detection.

// When collides with something
function OnTriggerEnter(other : Collider)
	// gets the BlockS Object
	var block = gameObject.Find("BlockS");
	// Gets the movement script on the blocks object
	var movementscript = block.GetComponent(BlockMovement);
	// if the block collides with the floor
	if( other.gameObject.tag == "WallFloor")
		movementscript.enabled = false;		

umm collision detection doesnt really work if your going to transform move stuff.

If you need collision detection you need a rigidbody, you normally move rigidbodies with physics. If your moving them with transform move you should mark as is kinematic. That means it will not be moved by physics but by transform.

A kinematic rigidbody which you want to move should be done during FixedUpdate to apply collisions properly.

if you would like to know which side you hit you may raycast to the object

this code snippet shows a raycast you could perform on collision.

//this ray will generate a vector which points from the center of 
//the falling object TO object hit. You subtract where you want to go from where you are
Ray MyRay = ObjectHit.position - ObjectFalling.position;

//this will declare a variable which will store information about the object hit
raycasthit MyRayHit; 

//this is the actual raycast
raycast(MyRay, out MyRayHit);

//this will get the normal of the point hit, if you dont understand what a normal is 
//wikipedia is your friend, its a simple idea, its a line which is tangent to a plane

vector3 MyNormal = MyRayHit.normal;

//this will convert that normal from being relative to global axis to relative to an
//objects local axis

MyNormal = MyRayHit.transform.transformdirection(MyNormal);

//this next line will compare the normal hit to the normals of each plane to find the 
//side hit

if(MyNormal == MyRayHit.transform.up)
you hit the top plane, act accordingly
//important note the use of the '-' sign this inverts the direction, -up == down. Down doesn't exist as a stored direction, you invert up to get it. 

if(MyNormal == -MyRayHit.transform.up)
you hit the bottom plane act accordingly
if(MyNormal == MyRayHit.transform.right)
hit right
//note the '-' sign converting right to left
if(MyNormal == -MyRayHit.transform.right)
hit left

compare mynormal to transform.forward and -transform.forward for the front and back plane.

now you simply stop movement in the appropriate way. Please mark as answered. :slight_smile:

“How can I detect which SIDE of a box I collided with?”

The very simple, absolutely reliable, way to do this is just add six colliders, one on each side

It’s then extremely easy.

After all, say you have a car model. This is precisely what you do to detect collisons on, say, the doors versus the roof or the various bumpers.

Enjoy - it’s very easy.

Here is code above working in C#


using UnityEngine;
using System.Collections;

public class GetSideHit : MonoBehaviour {		

	** Make sure to add rigidbodies to your objects.
	** Place this script on your object not object being hit
	** this will only work on a Cube being hit 
    ** it does not consider the direction of the Cube being hit
    ** remember to name your C# script "GetSideHit"

    void OnCollisionEnter( Collision collision ){
		Debug.Log( ReturnDirection( collision.gameObject, this.gameObject ) );
	private enum HitDirection { None, Top, Bottom, Forward, Back, Left, Right }
	private HitDirection ReturnDirection( GameObject Object, GameObject ObjectHit ){
		HitDirection hitDirection = HitDirection.None;
		RaycastHit MyRayHit;
		Vector3 direction = ( Object.transform.position - ObjectHit.transform.position ).normalized;
		Ray MyRay = new Ray( ObjectHit.transform.position, direction );
		if ( Physics.Raycast( MyRay, out MyRayHit ) ){
			if ( MyRayHit.collider != null ){
				Vector3 MyNormal = MyRayHit.normal;
				MyNormal = MyRayHit.transform.TransformDirection( MyNormal );
				if( MyNormal == MyRayHit.transform.up ){ hitDirection = HitDirection.Top; }
				if( MyNormal == -MyRayHit.transform.up ){ hitDirection = HitDirection.Bottom; }
				if( MyNormal == MyRayHit.transform.forward ){ hitDirection = HitDirection.Forward; }
				if( MyNormal == -MyRayHit.transform.forward ){ hitDirection = HitDirection.Back; }
				if( MyNormal == MyRayHit.transform.right ){ hitDirection = HitDirection.Right; }
				if( MyNormal == -MyRayHit.transform.right ){ hitDirection = HitDirection.Left; }
		return hitDirection;