[Sidefx-houdini-list] accumulating particles

Jerry Corda-Stanley jerry at intelligentcreatures.com
Mon Feb 25 11:07:44 EST 2008


you could try this as a hack.
create a particle system and have the particles split on collision.
The split particles have a semi transparent sprite attached to them.

taking a top down view of your scene you can do a GL render of the ground
plane and turn off GL viewport redraw. You'll have to expose that from the
interface parameters as it's hidden now. This will stop redraws for every
frame and graphically accumulate as the sprites build, their alphas gradually
layering up and they'll become more opaque. This can be rendered out, and the
resulting maps opacity used to define a height map for the built up surface.



----- "Jeff Wagner" <jeff at sidefx.com> wrote:
> There is doubtless a more current method to affect
> a similar effect.
> 
> Yep. H9(.1) has a few ways to do feedback. Building your POPs inside a
> 
> DOP sim then using a SOP solver to read the particle cache and do your
> 
> work there should offer you the missing functionality. You could 
> generate your point cloud in the SOP solver per iteration...
> 
> There is also the "time*" SOPs (time blend, time shift, time warp)
> along 
> with the foreach SOP to do time based shifting and feedback.
> 
> 
> -jeff
> 
> caleb at howlor.com wrote:
> > 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
> > Dogs".
> >
> > 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!
> >
> >
> > -caleb
> >
> > 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-?
> >
> > Thanks!
> >
> > Jed-
> >
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