How to add and remove particles in a ParticleSystem?!

[novemrain]

I'm writing a little game including some bullets and explosion.
So I think using ParticleSystem is a good idea.

The problem is : adding and removing particles from the ParticleSystem are very often.
In every frame , I need to compute each particle's position and change them in the ParticleSystem
Sometimes,when new bullet come or old bullet die,I also need to add or remove vertex in geometry in ParticleSystem.

Now my way to solve this problem is so stupid,it already make my FPS lower when I shoot bullet
All I want is to find a fine way to make it optimistic !

My way is here
if there is bullets in the scene
every frame I update it like this

// First. remove the PS from scene
scene.remove( this.particles );

// Then. new a geometry and compute each bullet vertices's position,for they are flying!
this.geometry= new THREE.Geometry();
for(....)
    // to do some compute,then add vertices to geometry
    this.geometry.vertices.push( new THREE.Vertex( this.bullets[i].position ) );

// Then. new the ParticleSystem with the geometry
this.particles = new THREE.ParticleSystem( this.geometry, this.material );

// Finally. add it back to scene
scene.add( this.particles );

OK,it got no problem when I run it,but it's really slow
I think there is no need to do the 'remove','new',or 'add' every time
I just need to
change the position of vertices
and add or remove vertex
There must be some 'clever' way

and I know

geometry.__dirtyVertices = true;
geometry.__dirtyElements = true;

maybe it can solve this problem?
But when I add vertex it shows nothing added
when I remove vertex the chrome totally stopped
I must do something wrong

So,what is the right clever way?
Thank you

[mrdoob]

You can't add or remove particles from a particle system. But you can work around it by first adding as many vertices as particles you may need into the ParticleSystem. Then moving the unneeded particles away of the camera view and then moving back to the position when needed and doing geometry.__dirtyVertices = true; for updating it.

[novemrain]

Thank you
BTW,I set the FPS of my game at 45,
Sometimes it is only 20 when I shooting
is that too low for a onlinegame,or just OK?

[mrdoob]

Going down to 20 is no good... I challenge you to get steady 60fps! ;)

[novemrain]

Ok.I will try

Another question,how to do Collision-Detection using threejs?
Maybe my words are not clear,do you know what I mean?
For example,there are two helicopters in my game,if they get a collision they are supposed to explode
So,how to detect if objects(in the scene) got Collision with other objects?

Thank you

[mrdoob]

That has nothing to do with the this issue. Better open a new issue with your new question.