Which approach to use for collision direction?

hi,

i am an experienced C# developer and started learning unity some weeks ago. I already created a game in XNA that does the same i want to achive with unity, so this is a "learning game project" for me.

What i want to do is creating a game similar to this: http://www.youtube.com/watch?v=J2Fyow70A1Q

...i have been playing this a really long time ago.

The "ball" is my player object. It has a rigidbody attached to detect collitions - it's not controlled by physics since this would not work that good in this game.

I want the ball to behave different, when it hits a brick or the walls, depending which part of the ball (top, bottom, left, right) has hit the brick or the walls. For example: bounce a bit to the left, when a brick was hit with the right side of the ball (as you can see in the video), change the move direction of the ball, when it hits with it's top/bottom.

So i do not only need to find out if a colission has occured - i also want to find out, which part (top, bottom, left, right) of the ball has collided. I tried, placing invisible blocks at the top, left, right, ... of the ball and use these blocks for colision detection but i don't know if this is a good idea so i wanted to ask unity developers with more experience, how you would solve this?

Unfortunately i found not tutorial for this - there are many tutorials for collision detection, but non where it matters, which part of the object collided.

thx for you help,
Hannes

 

Use OnCollisionEnter or OnCollisionStay: http://unity3d.com/learn/tutorials/modules/beginner/physics/on-collision-enter

Then you can use normals:

http://docs.unity3d.com/Documentation/ScriptReference/Collision-contacts.html

 

hi,

i finally got it working the way i want, applaying some minor changes to the code from: http://answers.unity3d.com/questions/339532/how-can-i-detect-which-side-of-a-box-i-collided-wi.html

Code (csharp):

1.  
2. // create particle effect at collition point
3. ContactPoint contact = collision.contacts[0];
4. Quaternion rot = Quaternion.FromToRotation(Vector3.up, contact.normal);
5. Vector3 objectHitPosition = contact.point;
6.  
7. if (collisionParticles != null)
8.     Instantiate(collisionParticles, objectHitPosition, rot);
9.  
10. //this ray will generate a vector which points from the center of
11. //the falling object TO object hit. You subtract where you want to go from where you are
12. Ray MyRay = new Ray(objectHitPosition, objectHitPosition - this.transform.position);
13.                
14. //this will declare a variable which will store information about the object hit
15. RaycastHit MyRayHit;
16.  
17. //this is the actual raycast               
18. Physics.Raycast(MyRay, out MyRayHit);
19.  
20. //this will convert that normal from being relative to global axis to relative to an objects local axis
21. Vector3 MyNormal = MyRayHit.normal;
22.  
23. //this next line will compare the normal hit to the normals of each plane to find the side hit
24. MyNormal = MyRayHit.transform.TransformDirection(MyNormal);
25.  
26. if(MyNormal == MyRayHit.transform.up)
27. {
28.     //you hit the top plane, act accordingly
29.     print ("Hit TOP plane");
30. }
31.  
32. //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.
33. if(MyNormal == -MyRayHit.transform.up)
34. {
35.     //you hit the bottom plane act accordingly
36.     print ("Hit BOTTOM plane");
37. }
38.  
39. if(MyNormal == MyRayHit.transform.right)
40. {
41.     //hit right
42.     print ("Hit RIGHT plane");
43. }
44.  
45. //note the '-' sign converting right to left
46. if(MyNormal == -MyRayHit.transform.right)
47. {
48.     //hit left
49.     print ("Hit LEFT plane");
50. }
51.