[Sidefx-houdini-list] POP particles rotation situation here...

Pablo Giménez pablogipi at gmail.com
Thu Jul 14 05:22:22 EDT 2011


Well in big and small productions is handle in the same way: smart
expressions :)
AS far as I remember, I dont have houdini in front of me at the moment, what
I do to accumulate a values is always use the local variable and then add my
stuff, this will carry on the values for the next operators.
Rotation POP and Torque POP are complitelly different things. All operators
that modifies forces just pick up the current accel values and add it's own
force, this is the reason because you can mix them in the same network.
Different thing is for operators that directly sets an attribute. Like
velocity or rotation. It doesnt matter if you use expressions or a VOP POP
you have to carry on the previous values.
If you want to do this for the rotation angle in a rotation POP you have to
do something like: $ROTA + [myStuff]. And it should be able to concatenate
several rotation POP.
Same for other values.
For instance if you want to animate this rotation angle you can do it in two
ways:
$FF % 360
$ROTA + 5
Both eorks but the first just override the currentvalu with something that
is getting bigger in a sequence [0-359], the second add to the current value
5 degrees. For me the second option is much better.
Well this what I remember now on top of my head, hope this helps.

2011/7/14 Javier Meroño <javiermerono at hotmail.com>

>
> Here´s an interesting one I just bumped into.
>
>
>
> I want to add several (different) rotations to my POP particles. I
> noticed you can´t chain several Rotation POPs: it only applies the last
> one. My best guess being the reason for this is the Rotation POP assigns
>  the actual rotations to the particles, just like the velocity assigns
> velocity as opposed to being a force that adds to it.
>
>
>
> Hence, I go for the Torque POP, which indeed does work and allows several
> of them to be concatenated as they are forces.
>
> BUT, obviously I want to limit the Torque to one or two frames.
> Otherwise it adds up every frame and I get too much angular velocity.
> The problem being my particles are "activated" by putting them inside a
> group which is preserved.
>
> I solved the situation by adding another non-preserved group that activated
> the torque force.
>
>
>
> Is this how you usually deal with several rotations?
>
>
>
> Also, I would like the angular velocity to to get increasingly higher as
>  the particle moves more, so I add an angular velocity node and use
> something along the lines of
>
>
>
> $WA*(0.3*vlength(vector3($VX,$VY,$VZ)))
>
>
>
> which more or less works, with the exception of one or two particles that
> would require some "individual" love.
>
>
>
> All of this seems a tad messy and unelegant to me. How do you usually
> deal with this....do you go the VOP POP route? Just trying to understand
>  how it is usually done in big productions....
>
>
>
> regards,
>
>
>
> Javier Meroño
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>



-- 
Un saludo
Best Regards
Pablo Giménez



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