[Sidefx-houdini-list] accumulating particles

caleb at howlor.com caleb at howlor.com
Tue Feb 19 12:26:26 EST 2008

In the absence of a Feedback SOp, I sometimes write particles out to a
file, and then read them back on the next frame by means of a VEx POp, or
another type of custom operator.  The only real awkwardness of this method
is that it necessitates executing one's playback from an output node - to
get the sequence to write.

By reading in the previous frame's particles, and using point cloud
functions to suss the previous state, and modify the behaviour of the
particles on the current frame according to what came before, I've been
able to affect some pretty interesting behaviour.  Stacking snow by this
sort of mechanism should be pretty easy.

Of course, I started doing this right after the Feedback SOp was taken out
of PRISMS - in protest.  There is doubtless a more current method to affect
a similar effect.

This is how I did the perception systems for the flying snakes in
"Elektra", crowds in "The Sum of all Fears", and 16,000 mice in "Cats and

Point clouds make it *fast* to handle huge numbers of particles, and allow
for more stable, and abrupt interaction than the falloff model employed by
the interact POp.

I love me some particles!


Original Message:
From: Jed Schwartz jed at jedschwartz.com
Date: Tue, 19 Feb 2008 10:03:29 -0500
To: sidefx-houdini-list at sidefx.com
Subject: [Sidefx-houdini-list] accumulating particles

I'm suffering from a Particle brain freeze-- I need to accumulate  
particles on top of particles- (like accumulating snow) Stick on  
contact puts particles in place on the ground plane-- how do I get  
the following particles to stick to the existing "stuck" particles-?



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