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

Michael Dunkley mdunkley at gmail.com
Fri Mar 18 17:40:02 EDT 2016


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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