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

Larry Giunta larry at gcreativestudios.com
Sat Mar 19 11:05:59 EDT 2016


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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