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Which approach to use for collision direction?

Discussion in 'Editor & General Support' started by HannesB, Oct 26, 2013.

  1. HannesB

    HannesB

    Joined:
    Oct 29, 2012
    Posts:
    10
    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
     
  2. hippocoder

    hippocoder

    Digital Ape Moderator

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  3. HannesB

    HannesB

    Joined:
    Oct 29, 2012
    Posts:
    10
    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.  
     
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