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Old 11-20-2012, 07:25 AM   #1
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David Johnson
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nCloth strength to zero

This is something that has been bugging me for a while now. Often, when I'm using nCloth inputMeshAttract or a dynamic constraint, I want to animate the attraction or strength starting from some value to zero (or vice versa) in a gradual way. The problem I seem to encounter is that there is a noticeable difference between 0.001 (or any non zero value) and zero. It means I can always see the point of change between zero and non-zero, unless I'm careful to choose a moment where something else is masking it.

Am I approaching this the wrong way maybe? Any suggestions?

thanks
David
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Old 11-20-2012, 08:10 AM   #2
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Been there before.
I first started to notice when using ramps to drive attributes. I would always have to type in really really small values and make sure the transition where very gradual. Other than taking note of attributes that have the most nonlinear properties. There is much i can think of to help.
Internally nCloth tries to protect users from complex attributes. So that the values you generally use will feel "nice". Like if i set input attract to 1 it sort of feels like it does something i would want. This works for the most part. However it starts to fall apart when you really want to fine tune things.

I've asked for the nonlinear offsets to be exposed so you can manipulate them. But i haven't had much luck get them to fix the lift space scale bug. Because it would affect backwards compatibility. So i don't see that happening. Duncan

I can only subject that you keep going smaller. Maya can handle much greater precision than the UI likes to show. Just type 0.0005 in the attribute and watch it snap to 0.001. But if you look in the channel box you will still see 0.0005. So just keep going smaller.
 
Old 11-20-2012, 12:28 PM   #3
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Thanks Scott I'll give it a try.

+1 for the lift thing. Working with characters that change speed all the time makes it difficult to control that one, and often I end up with a mess of keyed values that are hard to keep track of through revisions to the main animation. Lately I've been using the SOuP plugin to drive some of these attrs using the per-point velocity of the input mesh (or sometimes the cloth - but thats a bit tricky). It works ok except for the extra compute overhead.

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Old 11-21-2012, 01:10 AM   #4
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Have you tried using textures (ramp, noise) in dynamic properties map tab? I have been getting a good result with it. with the input mesh attract set to 0.1 or 0.5 and the ramp color range between 0 to 1 I can get mostly whatever I need.
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Old 11-21-2012, 11:50 AM   #5
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No. I've only ever used per-vertex weights, painted in artisan, or sometimes imported from a file. I'll try some textures and see if it works better. Thanks for the suggestion.

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Old 11-26-2012, 05:39 PM   #6
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this is just a guess as I'm on holiday, so dont have maya handy to test...

but are you guys keying off the damp also?
I would assume this is calculated, or not, depending on if the strength it relates to is !=0

I know the damp on the inputMeshAttract used to by calculated incorrectly and push the cloth ahead of the inMesh in certain situations.. I believe this was fixed in 2012 though... just a thought

what exactly are you referring to with the "lift space scale bug"?

.j
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Old 11-26-2012, 09:04 PM   #7
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Thanks for the suggestion John. I will check out the damp idea. You're suggesting I lower it at the same time as I lower the strength, right?

I've seen the inputAttract problem, pretty much as you describe it, in 2013. I dont remember noticing it in 2012, so maybe it was fixed but got broken again, or maybe I'm seeing something different. Either way I had to abandon inputAttract and use matching mesh constraints for my current project which involves characters stopping and starting their motion quite suddenly. With inputAttract the cloth always seemed to lag on the first frame of motion, then overtake it and it is very hard to bring back under control. MatchingMesh constraints seem so much easier to tame in this regard.

Regarding lift... actually I'm not exactly sure what Castius was referring to, and I probably wouldn't call it a bug, but I assumed he meant the relationship that the lift value seems to have with velocity. That is, when velocity of the cloth increases the effect of lift increases dramatically. I read something Duncan wrote about the way the calculation is taking some short cuts, but I cant remember the details.

David
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Old 11-26-2012, 10:33 PM   #8
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http://forums.cgsociety.org/showpos...786&postcount=6

I just ran my test scene and it's even worse in 2013.
 
Old 11-26-2012, 10:47 PM   #9
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Thanks for the info Castius. I had to read that about 5 times before it made sense, but I think I get it now.

David
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Old 11-27-2012, 05:28 PM   #10
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Quote:
Originally Posted by djx
Thanks for the suggestion John. I will check out the damp idea. You're suggesting I lower it at the same time as I lower the strength, right?

yep

Quote:
Originally Posted by djx
I've seen the inputAttract problem...
Either way I had to abandon inputAttract and use matching mesh constraints...

yeah, constraint will always give you more control. not sure if matching mesh uses pontToPoint or pointToSurface though.. if it uses pointToPoint, I would sugest making a pointToSurface constraint instead so you have control over the tangent strength also, so it can move off the driving surface if needed for collisions etc...

Quote:
Originally Posted by djx
Regarding lift...

I read the other link, hadn't really noticed it as we always work at the same scale.. although recently did some enormous bird feathers and noticed some odd lift behavior, so this might be related. I couldn't change the solver scale though.. so making 10 foot feathers is probably always an issue

thanks for the info guys

.j
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Old 11-27-2012, 05:28 PM   #11
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