I need to find out where a particle collided on the collider. I've been googling for over and hour now and haven't found anything yet. Basically, I can't use a raycast technique because the 'bullets' I'm firing aren't moving very fast. I'd like to spawn an explosion where the particle collided.
It seems from what I've read that such a thing is impossible to tell. This is odd because obviously the particles can reflect off of a collider, but it doesn't seem that the position information can be passed through OnParticleCollision. Also, I don't think particles can set off OnCollisionEnter (tests have shown this to be the case) so I cannot get any collision information.
This seems like such a simple thing to implement. If I can't get this information from the OnParticleCollision event, I may consider creating two dimensional meshes with box colliders, but this seems like a huge waste of CPU resources.
We are actively working on collision messaging ATM and with any luck it should go into Unity 4.2. This will let you read collision impact points, incident velocity etc. With this data you can easily cause damage and/or apply forces to collidees.
What you probably want to do is make your "bullets" a gameobject with a rigidbody, and attach your particles to that. That way you can do normal collision detection, etc. You'll have to do movement of that object yourself, though.
Ok, well I figured out how I can do it. Kinda hacky though, I hate that...
Basically, each emitter object will have a script with an array of 'trackers' that track each of the emitted particles positions, velocity, and lifespan. Since I'm emitting the particles manually with a set direction, velocity, and energy, I can just use that information (provided there aren't any weird sync issues) to see where each particle is and then raytrace for a collision each frame. If one of the 'trackers' senses an impending collision, it can spawn an explosion at that spot.
It shouldn't matter than the trackers don't know which particle they're tracking since the particle will delete itself upon collision, I just need to be pretty sure that particle will hit. Essentially it's just an invisible parallel particle system.
Ugh, this is really hacky, if I don't dream of a better solution tonight I'll try it out tomorrow.