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

Larry Giunta larry at gcreativestudios.com
Wed Aug 23 15:34:30 EDT 2006

Hey Jerry,

I'm not sure if this would achieve
what I was looking for, but wanted
to try it out since it sounds like an
interesting approach.

However, I wasn't exactly sure how
I would go about rendering out a
position map?

Is that something I can render with the
geometry ROP??

Thanks again all for your helpful replies.


On Aug 23, 2006, at 12:56 PM, Jerry wrote:

> Hey Larry.
> You could try rendering out a position map of the surface to birth  
> from and apply that to the particles.
> The particles would then wave about on the surface. I guess you  
> could use the $LIFE as a lookup to
> switch between their normal behaviour and the wavy behaviour.
> Jerry
> 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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