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

Jerry jerry at topix.com
Wed Aug 23 12:56:15 EDT 2006

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.


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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