[Sidefx-houdini-list] Pop : Limit the number of particles

Timothy Stam timothystam at hotmail.com
Sun Mar 20 16:22:13 EDT 2016


You're most welcome, glad I could help!

> Date: Sun, 20 Mar 2016 20:37:29 +0100
> From: facialdeluxe at gmail.com
> To: sidefx-houdini-list at sidefx.com
> Subject: Re: [Sidefx-houdini-list] Pop : Limit the number of particles
> 
> Timothy it is working great !
> The npoints just has to reference a Sop node after the Popnet.
> If I reference the popnet itself it doesn't work.
>  if (npoints("/obj/geo1/popnet/") >= 167, 0, 1)
> If I reference a Point Sop (point1) which comes after the Popnet it works !
>  if (npoints("/obj/geo1/point1/") >= 167, 0, 1)
> And I can compare 2 different sop nodes !
>  if (npoints("/obj/geo1/point1/") >= npoints("/obj/geo1/sphere1/"), 0, 1)
> 
> Exactly what I was looking for ! Thank you Thimothy !
> 
> On Sun, Mar 20, 2016 at 5:45 PM, Timothy Stam <timothystam at hotmail.com>
> wrote:
> 
> > Hi Olivier,
> > You can use the following expression in the Impulse Activation parameter
> > on the popsource node:
> > if (npoints("/obj/grid/dopnet1/") >= 500, 0, 1)
> > so, if the number of points in dopnet1 exceeds 500, parameter value is 0,
> > else it is 1.
> > You have to reference a SOP node - I think - because in DOPs we use
> > particles, not points, where npoints() looks for points.When referencing
> > any of the DOP nodes it won't work for me.
> > This way it stops birthing as soon as I hit 500 particles.
> > I hope this is what you were looking for.
> > Cheers,
> > Timothy Stam
> >
> > > From: larry at gcreativestudios.com
> > > Date: Sat, 19 Mar 2016 11:05:59 -0400
> > > To: sidefx-houdini-list at sidefx.com
> > > Subject: Re: [Sidefx-houdini-list] Pop : Limit the number of particles
> > >
> > > Olivier,
> > >
> > > It would be great if you can follow up on this if you do find a suitable
> > solution.
> > >
> > > I was just trying to tackle this a few months ago for a potential
> > project.
> > > I never quite got it working exactly as I needed …. but the project
> > never happened either.
> > > So I just moved on.
> > >
> > > But it’s something I’ve had on the list to revisit because it has come
> > up a few times now.
> > >
> > > Good luck!
> > >
> > > Larry
> > >
> > >
> > >
> > >
> > >
> > > > On Mar 18, 2016, at 5:53 PM, Olivier Jeannel <facialdeluxe at gmail.com>
> > wrote:
> > > >
> > > > Hey Michael, thank you !
> > > > I'll try your solution on monday (weird this is a Detail, I would have
> > say
> > > > "Point" in the first thought)
> > > > I was thinking maybe also trying to work with particle states, but I'm
> > not
> > > > sure this (ice) feature exists in Houdini.
> > > >
> > > > On Fri, Mar 18, 2016 at 10:40 PM, Michael Dunkley <mdunkley at gmail.com>
> > > > wrote:
> > > >
> > > >> Hey Olivier, the pop source node automatically attaches a detail
> > > >> attribute, called "nextid", to pop geometry that describes which
> > > >> particle id is next in line to be used.  It's technically possible to
> > > >> reference this through expressions in your activation parameters.  So,
> > > >> impulse activation could be (for instance):
> > > >>
> > > >> detail("$DOPNET:popobject1/Geometry","nextid",0)<100
> > > >>
> > > >> Note that you may have to change "popobject1" depending on what your
> > > >> particle object is called.  popobject1 is the default name from the
> > > >> shelf operations.
> > > >> I suspect this is not a hundred percent solution, as that number would
> > > >> only be updated between cooks.  If you're emitting very slowly, then
> > > >> probably everything would be fine.  But if you're emitting 10000
> > > >> particles on frame one, it would birth all 10000 particles, then stop
> > > >> on the next frame (or substep) as "nextid" would then be 10001.  Might
> > > >> work well for efficiency's sake in concert with Steven's delete
> > > >> solution, so that you'd be both stopping emission and running cleanup.
> > > >>
> > > >> mike
> > > >>
> > > >> On Fri, Mar 18, 2016 at 5:10 PM, steven ong <steve_nong at pointy.tv>
> > wrote:
> > > >>> Hi Olivier,
> > > >>>
> > > >>> The POP Kill is deleting the particles.
> > > >>>
> > > >>> If you're trying to emit particles one after another, you have to
> > either
> > > >>> delete the points one by one in SOPs and set Emission Type to All
> > Points.
> > > >>>
> > > >>> However, in the old POPnet, you can put down a grid as a source and
> > in
> > > >> the
> > > >>> Source POP with Emission Type as "Points(ordered)", set Constant
> > > >> Emission to
> > > >>> $FPS so now you'll get a particle per frame in the sequence of the
> > point
> > > >>> number order of the grid.
> > > >>>
> > > >>> This functionality is missing from the new Source POP in DOPs. :(
> > > >>>
> > > >>> Cheers!
> > > >>> steven
> > > >>>
> > > >>>
> > > >>>
> > > >>>
> > > >>> On 03/18/2016 13:55, Olivier Jeannel wrote:
> > > >>>>
> > > >>>> Thank you François,
> > > >>>>
> > > >>>> But then, in Pop, how do you do you have the particles to move one
> > after
> > > >>>> the other and not all at once ?
> > > >>>> Thank you Steven,
> > > >>>> It works very well ! But should I consider that it delete
> > particles, or
> > > >> is
> > > >>>> the emission simply stopped ?
> > > >>>>
> > > >>>> Thank's for your help :)
> > > >>>>
> > > >>>> On Fri, Mar 18, 2016 at 9:47 PM, steven ong <steve_nong at pointy.tv>
> > > >> wrote:
> > > >>>>
> > > >>>>> Hi Olivier,
> > > >>>>>
> > > >>>>> You can do this very easily with the old POPnet as there is a "Max
> > # of
> > > >>>>> Particles" parameters. If you don't need the new POPnet
> > functionality,
> > > >>>>> you
> > > >>>>> can consider use the old version.
> > > >>>>>
> > > >>>>> Else, in a Pop Kill, you can use the following expression under the
> > > >> Rule
> > > >>>>> tab:
> > > >>>>>
> > > >>>>> if(@id>999)
> > > >>>>>    dead=1;
> > > >>>>>
> > > >>>>> That should limit the number of particles to 1000. Hope this helps.
> > > >>>>>
> > > >>>>> Cheers!
> > > >>>>> steven
> > > >>>>>
> > > >>>>>
> > > >>>>>
> > > >>>>> On 03/18/2016 13:39, Olivier Jeannel wrote:
> > > >>>>>
> > > >>>>>> Hi there,
> > > >>>>>> A very simple noob question :
> > > >>>>>> In  a Popnet, using a PopSource node, I'm using Impulse
> > Activation and
> > > >>>>>> Impulse Count.
> > > >>>>>> I would like the emission to stop when a certain ptnum is reached.
> > > >>>>>> I tried in Impulse Activation the following expression :
> > > >>>>>> if (@id >100, 0, 1)
> > > >>>>>> But no luck.
> > > >>>>>> I'm sure I've seen it somewhere inside one of the 300 tutorials
> > I've
> > > >>>>>> watched but I'm too dumb to find it :/
> > > >>>>>>
> > > >>>>>> Can someone give me the correct expression ?
> > > >>>>>>
> > > >>>>>> Thank you :)
> > > >>>>>> _______________________________________________
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