[Sidefx-houdini-list] particle birth - deforming source

Larry Giunta larry at gcreativestudios.com
Wed Aug 23 14:03:40 EDT 2006

Thanks Ben,

Yeah, all is great until the release.
Can't seem to figure out how to get
them unstuck once they are stuck.

I really can't have them release all
at once. They need to float off individually,
like at .7 of  $LIFE  for each particle.

Still trying.

Larry Giunta
Creative Director
G Creative Studios
larry at gcreativestudios.com

On Aug 23, 2006, at 1:04 PM, Ben Schrijvers wrote:

> Hi Larry,
> Just make another grid below the deforming one to birth particles  
> that shoot upward.
> Then a Collision POP to catch them with the deforming grid.
> Set it's behaviour to "stuck at collision" and switch on some  
> attributes in the attribute tab.
> After the sim (in sops) you can use these attributes to make the  
> particles (dis)appear.
> Then create a group on whatever condition to select the ones you  
> want to release.
> Hopefully (as I didn't try this) you can release the particles by  
> playing with $STUCK in a State POP.
> cheers,
> benS
> Larry Giunta wrote:
>> Kind of an interesting problem.
>> We're working on a close up, side shot
>> of the surface of bubbling soda.
>> We're trying to control one particle
>> system so the bubbles birth,
>> hangout/float on the surface ( which is an
>> animated deforming/rippling grid) then rise
>> up and out of frame.
>> We can get all the timing of events
>> correct by grouping particles based
>> on $LIFE, etc. before forces are applied.
>> The tough part is having the particles float
>> on the surface after they are born.
>> When they birth from the animating surface,
>> they stay where they are born ( don't
>> float on the surface).
>> A promising fix for this was to birth
>> particles from a flat grid then creep
>> the whole system on the deforming
>> surface back in SOPs. However, once
>> the particles rise up off the surface they appear to be flipping
>> all over the place because they are still essentially
>> being crept on the rippling surface.
>> This was a nice, fast solution but may
>> need to be abandoned because we
>> can't seem to control the erratic motion
>> when they rise above the surface.
>> Is there a way to birth particles from a rippling/deforming
>> surface but have the particles stay stuck to that
>> surface until a certain point in life ( when forces can
>> make it float off).
>> Been playing with the collision POP, but the interaction
>> is slow and not so predictable. Wondering if there
>> is an easier way. Will continue to search but thought
>> it might be worth posting this one.
>> Larry
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