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Control Hair Length with Falloff or Mograph?

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Jared Flynn
Control Hair Length with Falloff or Mograph?
on Jan 7, 2013 at 7:57:05 pm

Hey everyone!

I am about to start work on a project that will have me growing some tree roots. I plan to grow the main roots using splines and Sweep NURBS to maintain control over the shape & look, but I'd like to grow the smaller branching roots using Hair.

The problem I'm running into is getting the hair to grow gradually, from the head of the main root to the tail. Ideally I would like to do this using some kind of falloff, say a Plain Effector, but I can't seem to figure out how to link the Thickness map of the Hair material to something that can talk to Mograph effectors.

I feel like this is probably a fairly common technique but maybe I'm just not coming up with the right search terms to suss out the issue on my own. Thanks so much in advance for any guidance!

All the best & happy 2013,

Jared Flynn
Motion Graphics Designer
http://be.net/jkinetic


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Adam Trachtenberg
Re: Control Hair Length with Falloff or Mograph?
on Jan 7, 2013 at 9:06:45 pm

I suppose it's possible to use mograph, but here's how I would do it:

1. duplicate your sweep nurbs objects and convert them to geometry;

2. grow the hair on the duplicates and then hide the duplicates (not the hair);

3. In the duplicate hair material, enable length tab;

4. place a gradient shader in the hair length texture slot;

5. animate the gradient to match the animation of the sweep nurbs growth of your root objects;

6. copy the gradient shader and paste it into your hair material's thickness texture slot.

Will take some trial and error but works quite well because the sweepnurbs generates a very good UV map.


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Adam Trachtenberg
Re: Control Hair Length with Falloff or Mograph?
on Jan 7, 2013 at 9:10:31 pm

Here's a sample scene, FYI: 5175_rootwithgrowingrootlets.c4d.zip

This method also has the advantage of keeping the hairs stable. If you try to grow them on an animated sweepnurbs you'll have problems with the guides jumping around, because the generated geometry is changing from frame to frame.


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Jared Flynn
Re: Control Hair Length with Falloff or Mograph?
on Jan 7, 2013 at 10:48:03 pm

Thanks a ton Adam! I'd poked around with the idea of using an animated gradient in the Hair Length but I'd done a shoddy job managing the animation of the black & white gradient knots-- my results were jumpy and awful. This is definitely much closer to what I'm after!

Good tip re: growing the hair on the un-animated Sweep too; I think this will do the trick nicely.

Thanks again!

Jared Flynn
Motion Graphics Designer
http://be.net/jkinetic


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