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

Ben Schrijvers Ben.Schrijvers at framestore-cfc.com
Wed Aug 23 13:04:20 EDT 2006

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 
Hopefully (as I didn't try this) you can release the particles by 
playing with $STUCK in a State POP.


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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