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

Olivier Jeannel facialdeluxe at gmail.com
Sun Mar 20 15:37:29 EDT 2016


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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