[Sidefx-houdini-list] wires dynamic problem

Louis Dunlevy louisdunlevy at gmail.com
Sat Jan 17 04:30:16 EST 2009


Another thing to bear in mind is the Sop Solver if it helps to set some
of those wire object point attributes dynamically. Every wire object
parameter can be a varying point attribute instead as Mark points out.

An old hack is to use the primitive sop in the Sop Solver to do a final
correction on the wire length, just store the original length of the
wire before the sim and scale it appropriately per step in the Sop
Solver. With the primitive sop $PT is the first point in every prim so
getting the origin for each wire is easy.

If you're adding deformations on top of your sim though you may have to
adjust your velocities accordingly in the sop solver too. Use the change
in position caused by the sop solver, divide it by the sim timestep and
add it on top of the original velocity.. or something of that nature!
There might be new options for that on the sop solver now though..

Louis

guillaume at alamaison.fr wrote:
> Yes, I just found the solution :).
>
> Only the first point of my wire was animated by hand in SOP. I added this
> animation to all the points instead
> of just the first one and now it works perfectly !
>
> I found the problem because I didn't understand why the wire dynamics
> worked well on previous work with some fur animations. 
> I realized that each fur guides sent to the DOP was moving from root to tip
> points (as animation came from the copy sop
> template input). 
>
> In my current work, I was copying the animation of a character hand on the
> first point of a curve/wire, thinking that all the
> other points will be animated by the wire solver. Good to know (for me at
> least :) ) !
>
>
> Cheers
>
> Guillaume
>
>
> On Thu, 15 Jan 2009 11:09:32 -0800, Mark Story <mstory at xion.org> wrote:
>   
>> Hmmm ... that's odd.  I don't know if it would be a reasonable work 
>> around, but you can assign those attributes as a point attr and dial in 
>> the exact mount of stretching/bending you need along the length of the
>> wire.
>>
>> The particular behavior you describe I've never encountered before, 
>> (I've done a lot of work with Wire DOPs) but am interested in what might 
>> be happening ... if you can't solve the problem, please post a hip file 
>> on one of the forums so we can take a look.
>>
>> Good luck!
>>
>>
>> Mark
>>
>>
>>
>>
>>     
>>> I'm working on a simple DOP wire simulation. The setup is just one curve
>>>       
>
>   
>>> (rather long).
>>> At SOP level, the root of the curve is constrained on a keyframe
>>> animation.
>>> In my DOP network, I'm using "Use Deforming Geometry" in the Wire
>>>       
> Object.
>   
>>> I use a SBD Pin Constraint on the root points ( 0-3 ) and then check 
>>> "Constrain To Animation" to keep
>>> the SOP animation on the 0-3 points.
>>>
>>> My problem is that I can't find a way to avoid some stretching between 
>>> the pin points and the first point moved by the wire solver.
>>> To limit the stretching, I set a high value on the Linear Spring 
>>> Constant. It works fine for all the points, except
>>> between the "pin points" and the "solved points".
>>>
>>> Any tips to stop this stretching is welcome.
>>>
>>> Cheers
>>>
>>>       
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