[Sidefx-houdini-list] POP's: best way to threshold particle emission based on an point attribute

Louis Dunlevy louisdunlevy at gmail.com
Mon Nov 15 19:41:40 EST 2010


On 11/16/10 11:14, Rangi Sutton wrote:
> On 16 November 2010 09:41, Miles Green<Miles.Green at al.com.au>  wrote:
>
>    
>> Hi,
>>   does anyone have any recommendation's for the best/fastest/most
>> efficient way to birth particles from polygons based on a custom point
>> attribute?
>>
>> the two methods I currently have are;
>>
>> 1)  inherit the custom attribute into pops via the source node, then
>> follow it with a  kill Node that checks if the custom attribute is under
>> a certain threshold
>>   - NOTE: this seems wasteful to me as the particles are created and
>> then killed
>>
>> 2) use a scatter  in sops before the popnetwork to create birth points
>> on the poly, and then use a delete Node to delete those points where the
>> custom attribute is under a certain threshold
>>   - NOTE: this seems slower than solution (1)  above
>>
>> I ideally would like to use the custom attribute directly in the popnets
>> source node to specify that particles never get created if the custom
>> attribute is below a certain value
>>
>>
>>      
> Personally, I like making the points in SOPs before birthing in POPs.. it
> allows you to see the source points while scrubbing in the time line,
> without having to sim. Usually I'd add the source velocities here as well,
> letting me see those as vectors in the viewport.
>
> Scatter allows you to scatter based on an attribute, which might do you.
> However the scatter heaps and cull them back approach is good too.. maybe
> you could find a speed up by grouping them in vops then deleting the group?
>
> btw.. use an expression like this for your const birth rate:
>
> npoints(opinputpath("..",0))
>    
$NPT also works!
> To link the number of points being fed in to the number being birthed.
>
> Ah.. I see Peter's suggestion works for you ;)
>
> The custom attribute as a variable probably doesn't work because the varmap
> isn't passed through from SOPs to POPs, where as Cd is a standard var.
>
> Beers,
> r.
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