Preserve overall hair shape using maya Hair/nHair?

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  05 May 2013
Preserve overall hair shape using maya Hair/nHair?

Hi all,
is there any efficient way to preserve the look of hair during simulation using Maya hair or nHair?

something like the results of some shots in this cinematic :

(Katarina's hairs between 2:10 to 2:30)
  06 June 2013
The simplest is input attract, but it might not look natural. To get the bend preservation and hold the groom make sure the follicle start directions are set to "start curve base".(rest pose should also be "same as start", or "from curve" if you have rest curves. You need twist resistance in addition to bend resistance. Extra bend links is also very helpful.. particularly for hairs with a high segment count. However make sure the hairs have as few segments as possible. If using pfx output you can use the subsegments to smooth the result(uses a close fitting hermite interpolation). There is a problem with the twist resistance currently in nHair where it becomes degenerate for straight segments... thus the hair is free to twist about straight sections, so if you can avoid any totally straight sections near the base of the hair it will help.

Another technique is to create constraints... both between hairs (component to component... perhaps using max distance) and between the hairs and the head.
  06 June 2013
Thanks for the tips, Duncan!
I'd tried the component constraints before (by selecting output hair cvs), but it took very long time before the creation finished, and it appeared that everytime I pull back the animation time to start frame with output curves displayed on screen, it also took huge amount of time calculating something before being ready to move again. Hiding the curves or not displaying it (turning off curve view) eliminated this problem. Is it an inherent problem with current hair system or there is any setting I missed? Thanks again!
  06 June 2013
There were some problems with dirty propagation within the dependency graph that made hair with curve output particularly slow. As well the constraint creation script had a method of getting the hair indices from the selected vertices that was VERY slow for a large hair system. (among other problems it indirectly called listHistory per cv which ended up walking the entire set of follicles and curves for each cv) These performance issues have been fixed in Maya2014.

If you need to use an older version I don't know of any workarounds for the constraint creation slowness issue when using selected cvs. (it is hundreds of times faster in 2014) If it was a critical problem you could perhaps copy the file createNConstaint.mel from a 2014 build and put it in your local scripts area. I think it would still work in 2013... but it might need some minor modifications.

However the slowness with curves you can workaround somewhat by using pfx output for previewing and hiding the curves and follicles. (although 2014 will still be faster)
  06 June 2013
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