Kill particles randomly after specific frame

#1

I have emitted particles from a surface and have saved it at an “initial state”.
So there they are, now I want them to start dying randomly after frame 100. I am trying to change the “lifespanMode” after frame 100 and then give a random lifespanPP.

What happens is that when I hit frame 100 it pauses then they all die at once.

here is the expression


if(frame >= 100){
particleShape1.lifespanMode=3;
 
}
else
{
particleShape1.lifespanMode=0;
particleShape1.lifespanPP=rand(1,2);}

Why does this not work?

#2

You don’t need to change lifespan mode keep it in lifespanPP

$age0 = particleShape1.lifespanPP0;
particleShape1.lifespanPP = (frame>40 && rand(1)<.25)?0:$age0;

Basically this tells the particle that after frame 40, there’s 1 out of 4 chances to set the particle lifeSpan to 0 (thus deleting it), else keep its initial lifespan (lifespanPP0).

#3

Thanks, I finally got it to work by setting the lifespan mode to PP only and putting the expression in the runtime befor dynamics section.

I am getting familiar with Mel and how to use it, but expressions seems to use a whole different syntax which I am unable to find any documentation about.

I like your solution, it is very short and streamlined but I am not familiar with the “? operator” and the way you use the “:” in this equation.

#4

It’s the ternary operator and is just a a short version of


if(frame>40 && rand(1)<.25){
    particleShape1.lifespanPP = 0;
}else{
    particleShape1.lifespanPP = $age0;
}

Expressions are pretty straightforward, you can use the same syntax as in MEL, minus the non ‘live’ operations that are not recommended but still work (setAttr, getAttr etc…)

For particles there are a lot of variables that you can work with that work per particle, not per object. There’s no real reference that I know of, you can read stuff on http://www.tokeru.com/t/bin/view/Maya/MayaParticles if you’re curious

#5

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