How? Make particle return to worldPosition



Im not great at MEL, and spend way to much time on figuring stuff out. What I would like to achieve: Iv got particles floating around in the scene, driven by forces.
I would like to query the world positions and velocity of the
particles on a certain frame, say frame 50.
Then on frame 450 I would like the particles to return to
the positions and velocity they were at frame 50.
So far I have only tried to get them back to the positions of frame 50, with out any success.
What I have is:

vector $gPP = <<0,0,0>>;
float $currentTime = currentTime -q;
if ($currentTime == 50){
getAttr particleShape2.position;
$gPP = particleShape2.position;
//print $gPP;

if ($currentTime == 450){

 particleShape2.position = $gPP;

Can you please tell me if I`m on the right track, and give my a nudge in the right direction.



Are you doing this in the particle expressions editor, or somewhere else?
if it’s the expression editor, then you should be aware that local variables like your $gPP are reinitialized for every particle for each frame, so it doesn’t store you value once the current particle is done. In order to do that you should do this:

  1. create a vector per particle attribute on the particle shape (i.e. posStorePP)
  2. in your runtime expression paste this:

  if (frame == 50) posStorePP = worldPosition;
  if (frame == 450) position = posStorePP;


Thanks Azrail,

Ill try this first thing in the morning. Just after I posted I realized that I should have worked with.worldPosition.And then interestingly enough I came across.worldParticlePositionreading tonight, will do some research on it. What I basically need to achieve is a bunch of bacteria like organisms thats going to be projected on the Barberton rock in a museum. The bacteria needs to wiggle and move around over the rock and every now and then it needs to attract to a goal to briefly form a fossil like structure <like those fossilized worms and bugs you get>
Everything works fine except after I form the fossil like structure I can not get my particles to integrate back into the picture to wiggle around over the screen again to get ready to form the next fossil.



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