Further collision beyond the OnCollisionEnter() event

Question

I am creating a game where I need collision between blocks of the same colour to be acted upon. The blocks are children of gameobjects which act to create clusters of blocks - kind of like Tetris shapes. The rigidbody component thus belongs to the parent gameobject and OnCollisionEnter is called only when two parents collide. I have no problem identifying when matching blocks collide when OnCollisionEnter is called. Here is the code I use for that:

 void OnCollisionEnter(Collision collision)
     {
         foreach (ContactPoint c in collision.contacts)
         {
             if ((c.thisCollider.renderer.material.color == c.otherCollider.renderer.material.color)
                 && (c.thisCollider.renderer.material.color != Color.gray)
                 && (c.otherCollider.renderer.material.color != Color.gray))
             {
                 ScorePoint = true;
                 c.thisCollider.renderer.material.color = Color.gray;
                 c.otherCollider.renderer.material.color = Color.gray;
             }
         }

(the blocks are coloured gray after colliding with the same colour)

The actual problem I have is illustrated below. In the first frame the gameobjects collide and no matching colours are detected. The collision between the gameobjects holds until two matching coloured blocks are touching, but of course OnCollisionEnter will not be called. I have tried playing with the OnCollisionStay event but I haven't managed to do so without raising huge performance issues on mobile devices.

If anyone has any advice it would be greatly appreciated. Perhaps a solution which works only in this special case where all the individual blocks are cubes?

alt text

Answer 1

Answer by Huacanacha · Oct 18, 2013 at 02:56 AM

It seems like all your problems would be solved if each cube had it's own collider. Then you can just test each cube-cube collision for matching colors in OnCollisionEnter, rather than testing each child of the parent via the material at each collision point (which you are doing via the material of the collision points). You can still nest the cubes under a parent object so they move together, and you can still access the parent from the child cubes if necessary etc.

This should also perform somewhat better when processing the collisions as you don't have to test each collision point.

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MDurkin · Oct 18, 2013 at 10:09 AM 0

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Thank you for your reply. Everything I've read online seems to suggest that the rigidbody component of the parent 'swallows' the colliders of the children, so that OnCollisionEnter is only called for the whole parent object. Do you know of any way around this?

mattmanj17 · Oct 18, 2013 at 03:18 PM 0

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as long as the script is attached to each individual block, the parenting shouldn't matter. and if you parent all the individual blocks to an empty game object, then the parent wont even have a collider. as far as parent colliders "swallowing" child colliders, are you referring to this

Compound Colliders

in that case, as long as the script is attached to the child objects, and not the parent, and each child has its own ridged body, each child should still behave as an individual collider.

Further collision beyond the OnCollisionEnter() event

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