Particle Simulate Local And World Space question

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Guys

I need your help. The following script kills the particle when it get to the target. When I set my particle System to Emulate Local Space it can't calculate the particle position in World Space but my energy beam behaves like it should ( Direction wise but goes past the target). If I set the particles to World Space. It dies at the target cause the distance gets calculated in word space which is correct. What I want to do is simulate in Local Space ( Energy Beam looks behaves nice) But use the particles Word position to calculate the distance. Please see Video to clarify what I am trying to say.

https://www.youtube.com/watch?v=--QvAGjO8bw

 var laser : ParticleSystem ;
 var particles : ParticleSystem.Particle[];
 var target : Transform;
 var endpoint : Vector3;
  
  
 function Update(){
  
 }
  
 function LateUpdate() {
  
 InitializeIfNeeded();
   var lenght = laser.GetParticles(particles);
   transform.LookAt(target);
   endpoint = target.position;
  
   for (var i = 0; i < lenght; i++) {
  
  
  
   if(Vector3.Distance(target.position, particles[i].position) < 2f) {
   particles[i].lifetime = -0.1f; //Kill the particle
  
  
   }
  
   }

Answer 1

Actually it even says it in the API docs for Particle.position. You can use Transform.InverseTransformPoint() to get the world position in local space :)

 var targetLocal = transform.InverseTransformPoint(target.position);
 ...
 if (Vector3.Distance(targetLocal, particles[i].position) < 2f)

Also, it's a small thing but whenever you only compare distances ( Vector3.Distance(a, b) < x ) and you don't really need to know the actual distance in units, it's usually better to use properties / functions like Vector3.sqrMagnitude that don't do the last step of the Pythagoras formula to calculate the length of the distance vector (square root) which is a bit performance heavy.

 // particle emitter is at(0,0) in this object, so this is also the distance vector to target
 var targetLocal = transform.InverseTransformPoint(target.position);
     
 for (var i = 0; i < lenght; i++) {
     // distance vector between particle and target
     var distToTarget : Vector3 = particles[i].position - targetLocal;
     // compare the square of distance to square of your limit (2f) 
    if (distToTarget.sqrMagnitude < 4f) ...

Or even better, since you need to compare if a particle has gone past a certain point (if it's really fast, it might slip through your current check where it needs to be close to target) you could use dot product. It's a fast calculation that checks whether 2 vectors point in similar direction ( dot > 0 ) or opposite direction ( dot < 0 ).

 // particle emitter is at(0,0) in this object, so this is also the distance vector to target
 var targetLocal = transform.InverseTransformPoint(target.position);
 for (var i = 0; i < lenght; i++) {
         var distToTarget : Vector3 = particles[i].position - targetLocal;
         // if vector from particle source to target points in the same direction as
         // vector from target to particle, it means the particle has passed the target 
         if (Vector3.Dot(distToTarget, targetLocal) > 0) ...

Particle Simulate Local And World Space question

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