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

Timothy Stam timothystam at hotmail.com
Mon Apr 4 10:23:38 EDT 2016


Have you tried just bringing in one point without using a delete SOP or anything like that?
I imagine you can use a point wrangle node and use VEX to do an addpoint(), then vary the location of that point based on a variable like @Frame?That way it will always be the same point, only the location of it in space changes. That way you would have one point and one stream.
I'd test it out before suggesting but don't have time now so I'm just throwing it out there.
-Timothy

> From: larry at gcreativestudios.com
> Date: Fri, 25 Mar 2016 13:55:44 -0400
> To: sidefx-houdini-list at sidefx.com
> Subject: Re: [Sidefx-houdini-list] Pop : Limit the number of particles
> 
> ahhh … nice thought Olivier.
> Much appreciated.
> 
> ok, I’ll give it a go.
> 
> 
> 
> > On Mar 25, 2016, at 1:42 PM, Olivier Jeannel <facialdeluxe at gmail.com> wrote:
> > 
> > Maybe I'm wrong, but for the falling leaves I'd have them all already birth
> > at once and later give them some "falling" velocity selected by ptnum or
> > with an attribute transfer.
> > Le 25 mars 2016 17:25, "Larry Giunta" <larry at gcreativestudios.com> a écrit :
> > 
> >> This is really great Timothy,
> >> 
> >> Although I’m still trying to wrap my head around recreating some of the
> >> functionality from old pops.
> >> 
> >> If I try this method to birth just 10 particles it works great.
> >> However, if I have 10 points scattered on a tube, I tend to get 2
> >> particles birthing from one point … and then none from others.
> >> 
> >> If I jump down to Steve’s suggestion I can set up a delete SOP so I can
> >> feed one point at a time into the simulation.
> >> Set emission type to “all points” and it does birth from each points in
> >> order. Half the battle.
> >> 
> >> However, since that only leaves “Impulse Activation” available I have not
> >> been able to have it birth just one particle per point.
> >> It still wants to birth a stream at each point.
> >> 
> >> I’m need to explore Mike’s detail method further. The answer may lie there.
> >> 
> >> In my case I was trying to simulate a specific number of leaves falling
> >> off a branch.
> >> Slowly, one at a time. So it’s essential to birth only one particle per
> >> point as they are introduced into the simulation.
> >> 
> >> Thanks,
> >> Larry
> >> 
> >> 
> >>> On Mar 20, 2016, at 4:22 PM, Timothy Stam <timothystam at hotmail.com>
> >> wrote:
> >>> 
> >>> 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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