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Slow motion hair?

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Daniel Connell
Slow motion hair?
on Jun 27, 2005 at 5:46:50 am

I understand there's some way to interpolate a hair cache, but is there an easy way to slow the hair down as it's processing?

A true slow motion effect would be better, rather than just tweaking the damping etc, but if someone has some good settings for that.



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Chad Briggs
Re: Slow motion hair and Slow Motion in general
on Jun 27, 2005 at 2:21:23 pm

I'm not sure how the new hair system works, haven't used that much, but if you can bake the animation of the hair, you can map this animation to another time node, and animate that to get slow motion hair.

heres an example of getting slowmo with a simple scene.

make a nurbs sphere
set your timeline from 0 to 60
animate the nurbs sphere moving on the x axis from frame 1 to 30 far enough to make it somewhat zippy in speed.
now you should see the ball move when you scrub the timeline
go to the text selection box at the top of the maya interface and type in " time* " (without quotes)
this will select the built in time node
open the hypergraph and show input/output connections, you will see the time node
duplicate this node with default dupe settings
rename the new time node warpTime
select the warpTime node and the nurbsSphere object and show input and output connections in the hypergraph
you will see the warpTime node and the nodes for the nurbs sphere animation curves (something like nurbsSphere1_translateX) Middle mouse button the warp time node on top of the translateX nurbs sphere node, and choose other when it asks you to make a connection.
when the connection editor pops up, select the outTime field on the warpTime node side, and the input field on the translateX node side.
now if you scrub, you'll see that the ball has stopped moving.
select the warpTime node and go to the attribute editor
you'll see the Out Time vaule is at 0. On the default time node maya creates (the one you duplicated from) this vaule is typically designed to increment by one frame, giving you normal time. The new time node will not have that expression, so you can keyframe this field manually. The warp time node now acts as a "time control" for the existing keyframes on the nurbsSphere. Start keyframing the warpTime at various points on the timeline and watch what happens to the ball. For example keyframe the OutTime at 0 on frame 0. Go to frame 60 and keyframe the OutTime to 30. Now if you scrub, the ball moves twice as slow as it previously did, because it's taking 60 frames to get to frame 30 on the ball animation curve as opposed to 30 like it would in normal time.
So what does this have to do with the hair simulation? Well, if you back the hair sim, you should get animation curves like you did on the ball when you keyed it. This should allow you to follow the steps above with the baked animation curves and use the new time node as a way to achieve slow mo. The hair system may act as a particle cache type deal, in that case you'd plug it into the actual hair node/particle node via Time or currentTime instead of a animation curve.
hope that helps

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Steve Sayer
Re: Slow motion hair and Slow Motion in general
on Jun 27, 2005 at 4:50:22 pm

Depending on the requirements of the shot, there's also 'poor man's slomo,' which just involves putting a fractional value into the 'By Frame' attribute in Render Globals. Rendering by 0.5 frames instead of by 1 frame will also result in half-speed motion. 0.1 frames results in one-tenth-speed motion, and so on.

Of course this affects the entire shot, not just specific objects--and I'm not sure if it will work properly with hair specifically.

Might be worth a try, though.


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Glenn Moore
Re: Slow motion hair and Slow Motion in general
on Jun 30, 2005 at 12:23:00 am

You beat me to it Steve. I've tried that and it worked ok. I'm a poor man so it's ok. I'll have to try that other method. I assume it's a better way.

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Duncan Brinsmead
Re: Slow motion hair?
on Jun 27, 2005 at 9:12:36 pm

To slow down the hair you basically need to reduce all the forces acting on it. Lower the stiffness, the gravity, the intensity of any external forces, turbulence, drag and damp.


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Daniel Connell
Re: Slow motion hair?
on Jun 30, 2005 at 12:38:24 am

Thanks all for the feedback.

I ended up going with just tweaking the settings, the other approaches would've worked, but weren't ideal for the scene I'm working on.

If anyone's interested, these are the settings that gave a (not perfect but close enough) 4x slow effect:

stiffness 0.016
damp 0.05
drag 0.019
gravity 0.085


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