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

Larry Giunta larry at gcreativestudios.com
Fri Mar 25 13:55:44 EDT 2016


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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