[Sidefx-houdini-list] Particle Flow

Ben Schrijvers Ben.Schrijvers at framestore-cfc.com
Fri Mar 31 09:33:26 EST 2006

Basicly what you need to do to enable mixing your curve control with 
forces is modifying the acceleration rather than velocity.
Most of the other POP's work on acceleration as well and velocity is 
something to be very carefull with.
But you can't just use the attributeTransfer POP as this will overwrite 
the existing acceleration.
Also the acceleration that you need to apply is the difference between 
the curve velocity and the velocity of the particle.
So transfer the velocity to a custom attribute, subtract the particles 
velocity from it and add it to the existing acceleration.
You could do that with an expression in an acceleration POP.

The radius control is a bit tricky as the "blend width" parameter from 
the attrTransf SOP is missing on the POP version?
You could transfer the position of the curve to the particles, calculate 
the length between them and create your own weigth.. which you multiply 
with that own acceleration.

Personally I would build my own pop with VOP's. You can use the curve as 
a pointcloud and get attributes from it in that way.
Also you can control the radius in every way you want.. if you can 
translate that what you want into a bunch of VOP's.

Also take a look at the attractor POP. Put the curve through a point SOP 
and set the Dir F. in the forces tap.
This won't make the particles go along the curve though.. as you need to 
do the velocity difference as discibed above.


Jaideep Khadilkar wrote:
> Hi Everybody........
>   I had this question on the forum once, as, how to do, particle flow on  a curve, in Houdini, like Maya. I got one response, where we can modify  particle velocity, depending on the nearest tangent of the curve. It is  working fine. 
>   But the problem with this method is, that we can not modify the flow  using forces ( Fan, Gravity, Noise etc), after using velocity POP.  Also, in Maya, we can have Radius control for particles following the  curve, where we can determine, how packed, or seperate the particles  are, when they r following the curve. Can we design such thing in  Houdini?
>   Do u have any examples?
>   Plz. Help Me. Thanking in advance.
>   --------iamjaideep80
>   Jaideep Khadikar
>   TD, Sciclone Motion Graphics
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