[Sidefx-houdini-list] Split POP confusion

Andy Nicholas andy at andynicholas.com
Wed Oct 22 18:31:43 EDT 2008


Ha! Awesome, thanks a lot Jim, that should solve it. I'll give it a go
when I get back to work tomorrow.

You know, I did find it hard to believe that Houdini couldn't handle this!
Even if it does seem to be exploiting a loophole rather than a feature by
design.

Thanks

Andy



> Ah yes.  You're both right, particles created from a Split POP don't
> return
> to the same stream.  However, Groups in POPs are global and this creates a
> loophole that you can exploit.  By adding the split particles to a base
> group you can trick POPs into being 'recursive'.
>
> Here is a thread on the SESI forums dealing with this.
>
> http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=6162
>
>
>
> On Wed, Oct 22, 2008 at 3:52 PM, Peter Robbinson
> <probbins at sympatico.ca>wrote:
>
>> Okay, I seem to be missing something then. It works for me.
>>
>> I generate particles from a grid, colour them, use a fan to blow some of
>> them; then split them.
>> The split particles are reacting to the fan, just as the original
>> particles are.
>> Provided I create a birth group name for the split particles, I can
>> split those with another split pop and those in turn will react to the
>> original fan.
>>
>> PeterR
>>
>> Andy Nicholas wrote:
>> > Thanks for the replys. Larry, I think you've hit the nail on the head.
>> It
>> > would seem that the way things are set up, a split node can never
>> split
>> > particles that it generated (since by definition they can never be fed
>> > into the Split's input connection).
>> >
>> > Wow, that totally sucks. It basically means that you can't do any sort
>> of
>> > recursive spawning of particles without putting down a separate Split
>> node
>> > and copying the tree for every level of recursion. Surely this should
>> be
>> > bread and butter for a decent particle system? I'm amazed that Houdini
>> > can't do it!
>> >
>> > As a workaround, I think the only way I can do this will be to do it
>> all
>> > in SOPs and use a SOP solver. Not ideal, but as far as I can see it
>> should
>> > work.
>> >
>> > Cheers
>> >
>> > A
>> >
>> >
>> >
>> >
>> >
>> >> On Wed, Oct 22, 2008 at 10:31 AM, Andy Nicholas
>> <andy at andynicholas.com>
>> >> wrote:
>> >>
>> >>> Thanks for the responses. You're right, if it was just a case of
>> getting
>> >>> it all to be affected by those nodes, I could probably rejig the
>> order
>> >>> and
>> >>> it'd work. One thing I neglected to mention though is that I need
>> the
>> >>> newly split particles to also be able to split themselves under the
>> >>> appropriate conditions.
>> >>>
>> >>> The only work around it would seem, is that I'd have to copy and
>> paste
>> >>> the
>> >>> whole POP network N times after each Split POP, where N is the
>> maximum
>> >>> number of generations of bubbles. Not exactly a great workflow :-)
>> >>>
>> >>> I just need the particles to be treated as normal particles, and not
>> as
>> >>> if
>> >>> they're totally separate, as they need to go back through the same
>> tree
>> >>> (i.e. with the split POP). The Collect POP doesn't seem to have any
>> >>> affect
>> >>> on any of this.
>> >>>
>> >>> So is there really no way I can just tell these new split particles
>> that
>> >>> they're exactly the same as the other particles? Do any of the
>> lineage
>> >>> type of attributes have any effect on this? How is Houdini keeping
>> track
>> >>> of which particles are which?
>> >>>
>> >> Place the gravity & collision nodes after the collect pop.
>> >>
>> >> source ----> split
>> >>     |               |
>> >>     |               |
>> >> collect <-------+
>> >>     |
>> >> gravity
>> >>     |
>> >> collision
>> >>
>> >> (hope this formatting works)
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>> >>
>> >>
>> >
>> >
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>> >
>>
>> --
>> "gravity is not a force, it is a boundary layer"
>> "everything is coincident"
>> "Love: the state of suspended anticipation"
>> "To get any appreciable distance from the Earth in
>> a sensible amount of time, you must lie."
>> "Easy, is not how you make a living."
>>
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