Canīt get any force working in a PfLow with fumeFX follow

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  04 April 2013
Canīt get any force working in a PFlow with fumeFX follow

Im trying to make a splash and Iīve simmed a smoke pass with FumeFX that has the right motion which Iīm using to birth and fumeFX follow(so long its working fine). Ontop of that I wanted to add some extra gravity and turbelence in Pflow but it doesnīt seem to affect the particles at all..

What would be the right workflow to add extra motion ontop of the fumeFX follow particles (I need to add some more gravity at some point to mimic water splashes.. the motion looks to much as smoke otherwise...)

Cheers and thanks in advance

Last edited by nidas : 04 April 2013 at 06:48 PM.
  04 April 2013
If the Force operator is evaluated before the FumeFX Follow and the latter has an Influence of 100%, the Force's influence will be lost - the Speed channel will be overwritten with the Fume's Velocity.

If you add a Force operator AFTER a FumeFX Follow, it will affect the particles, but as a Velocity and not as Acceleration.

Normally in PFlow, each particle has a Speed channel. When a Force acts on the particle, the Acceleration value of the force is applied to the particle to change its Speed. Over time, a Force will accelerate the particle gradually like in real world, unless another force acts against that (e.g. a Drag Force).

But with a FumeFX Follow set to 100% Influence, that accumulation won't happen. The Force will be applied on the current integration step, and then the resulting Speed channel will be completely wiped by the FumeFX Velocity. So if you are applying a Gravity, your particles won't be getting faster moving down, they will be moving down at a constant rate - the Gravity Force turns into a Velocity source instead of an Acceleration source.

If you would set the FumeFX Follow Influence to less than 100%, the Fume Velocity will be blended partially with the existing Speed from the previous frame. But since both the Fume and your other Force will be recorded there, your FumeFX will be blending the current Speed with a fraction of the previous step's speed, and a fraction of the other Force's influence. You have to play with the values to see if you can get a better result that way. You can also scale the Velocity by factors greater than 1.0 to get more of the FumeFX influence, but remember that this way a particle might move faster than the fluid that is driving it, and thus produce unexpected (although sometimes fascinating) results.

Hope this helps.
  04 April 2013
Thanks alot for your informative answer (as always!).
I think Iīll have to play with it alot more to see if I can get the particles to behave as I need ém to.

So Iīm not doing it wrong to just have a FumeBirth - FumeFX Follow - force - ...
And just try to adjust the percentage in fumeFX follow and the force multiplier...

  04 April 2013
Seems like something you would want to use an Ember Field for, no?
poof ~>Vimeo<~
  04 April 2013
Yea Ember would be awesome for this I guess... I havenīt played with it yet but I hope to catch up with the beta soon...
  04 April 2013
You might be thinking of Stoke MX which should be released tomorrow
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