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

Andrew Lyons tstexture at gmail.com
Thu Jul 14 11:04:32 EDT 2011


Yep,

To put it another way - with each cook of a POP network you sometimes
want to add new values to the values from the previous cook:

$VX + $ADDX
$VY + $ADDY
$VZ + $ADDZ

Otherwise you are replacing the values built up over all previous
cooks with new values.

Cheers


2011/7/14 Pablo Giménez <pablogipi at gmail.com>:
> 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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>> Sidefx-houdini-list at sidefx.com
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>>
>
>
>
> --
> Un saludo
> Best Regards
> Pablo Giménez
> _______________________________________________
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>



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Andrew D Lyons | Digital Artist | http://www.tstex.com
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