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Hair and Hair Collieder

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Tony Barone
Hair and Hair Collieder
on Jan 10, 2012 at 5:51:19 pm

I've been trying to figure out how to get the Hair Collider Tag to work.

My 3D scene is for a still rendering, not an animation. Its simply 2 gardening tools sitting on the ground with Hair creating grass along the terrain. I applied the Hair Collider to the gardening tools, but its not affecting the hair at all.


Thanks.



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 10, 2012 at 7:25:09 pm

You have to run the animation forward in order for the dynamics to take effect, even if you're only rendering a single frame. Once you do that you can, if you like, freeze the hair with the Simulation>Hair Edit>Set as Dynamics command.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 10, 2012 at 10:41:29 pm

Thanks again for your help Adam, but I'm still not able to get the thing to work.

I've attached my file, can you let me know what I'm doing wrong here?

Note: I've set the hairs pretty low just for testing purposes to get it to update faster.

3524_hairtest.zip



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Brian Jones
Re: Hair and Hair Collieder
on Jan 11, 2012 at 5:22:51 am

you'll have better success if you turn off the colliders then let the grass fall through the floor then reverse the gravity and then let the grass rise up to deflect off the colliders (turned back on).
Still that's not going to be real successful since there is too much space between the points of the landscape and since the hairs average themselves between the guides if you have a guide to the left of the shovel and the next is to the right all the hairs in-between will go right through the shovel. So if you make the landscape mesh denser then redo the hair on the new object and do the fall/rise thing it would be a start.
A couple other things (other than playing with the collision settings) you can do is make the dynamics affect the hairs and not just the guides (slower but more accurate) and since you will still likely get some hair penetration, you can also use Proximal in the Length channel of the hair (set to the tools) to make the hair right under the tools shorter.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 11, 2012 at 2:55:59 pm

Thats obviously all I want, to make the grass beneath the tools shorter, or "pushed down" by the tools.

I tried the proximal in the length, but that make the grass disappear entirely for some reason, I put the tools into the "objects" portion of the proximal settings.



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 11, 2012 at 4:10:43 pm

A more direct approach would be to animate the tools actually moving down the ground. Do it slowly to lessen the chance of penetration.

I agree with Brian that you're going to have penetration issues with so few guides, but instead of using hair-level dynamics you can also increase the guide count. Worth a shot, anyway.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 11, 2012 at 4:50:17 pm

I think part of my question is being missing, or I am not asking correctly...

I am having trouble with the collision settings. Whatever I seem to set them at, they don't make a difference with the hairs.

I have the hairs set to a low number just for testing purposes as higher settings slow things down tremendously.

Can someone please explain how my collider settings should be to effect the hair? This is my first time ever using the hair features.

Thanks.



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 11, 2012 at 5:29:33 pm

I don't think the collider settings are going to make much difference. You probably need to adjust the dynamics settings in the hair object. Presently you're using very stiff settings. The "ridgid" checkbox makes a very big difference in terms of stiffness. With that checked you might need to lower the actual stiffness parameter to 10% or lower.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 11, 2012 at 6:12:35 pm

ah... I'm starting to see. Didn't realize I had rigid checked, thanks for pointing that out. Guess in my trying to figure this thing out, I figured they should be rigid.

Things are starting to get to where I want them.. I think.

I setup a short animation of the tools slowly falling onto the ground, as you suggesting and that seems to be doing the trick. Still, some hairs are poking through the shovel for some reason. Any idea how I can prevent that?

Also, when its where I want it to be. Is there a way to "freeze" the grass into the position its in and save it that way, so in the future I wouldn't have to re-run the animation to get it there?



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 11, 2012 at 6:56:39 pm

The grass poking through could be a result of too few guides, if you're applying dynamics to the guids rather than the hairs. Or it might be the result of settings in the hair material which aren't calculated when dynamics are applied to the guides.

You can use Hair edit>Set as Dynamics to freeze the hair position. If you do that you'll then want to turn off dynamics to prevent further motion (and to speed up the display).

Rather than go round and round adjusting parameters, I would just get the hair close and then use the brush and other tools to push penetrating hairs back under the tools.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 11, 2012 at 7:55:12 pm

Where is "Hair edit>Set as Dynamics" ?

I've looked just about everywhere I can think of. I'm using C4D R13.



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 11, 2012 at 8:31:49 pm

It's under the simulation menu.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 11, 2012 at 8:46:20 pm

Thanks! Obviously the one place I didn't look!

I really appreciate all your help on this thread... been learning a lot about this part of C4D thats remained a mystery for so long!

Can you tell me what the best way is to "fill in" a grass area?

I've tried several settings and some, such as increasing the guides count and hairs count seem to make the most difference. Increasing just the guides seems to slow things down a lot more than increasing hairs.

The "Fill Hairs" settings don't seem to make a noticeable difference.

And the "Cloning" setting within the Hairs setting also doesn't do what I would expect.

You seem to know quite a bit about this portion of C4D, would really appreciate you shedding some more light on this, or pointing me in a direction where I could learn more elsewhere.

Thanks again!



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 11, 2012 at 11:02:49 pm

Increasting the number guides has no effect on the number of hairs. It's mostly useful for styling and to increase the accuracy of simulation.

Fill hairs, OTOH, should increase density and would be the method I'd recommend for grass.

From the help docs:

"Simply said, fill hair is additional hair that is interpolated between existing hair when the scene is rendered. This lets you render objects with a lot of hair, even millions (e.g. fur), while keeping render times down and saving on memory. When applying fill hair, make sure you use relatively little real hair since the interpolation between very much real hair can take a very long time. Fill hair will also be created if you assign a Hair material directly to an object to which hair is not assigned."

Cloning allows you to use custom object in place of hairs, so not applicable here.


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Tony Barone
Re: Hair and Hair Collieder
on Jan 12, 2012 at 2:55:59 pm

Adam, thanks again for all your help. I took some time to go through the manual and learned quite a bit from there as well. I hadn't realized how much Maxon had improved the help system since the last time I took a look at it!



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Adam Trachtenberg
Re: Hair and Hair Collieder
on Jan 12, 2012 at 7:19:19 pm

Yeah, the help system really is great. You can r-click on the name of any parameter and get a link that will take you directly to the relevant spot in the help docs. As many years as I've been using Cinema, I still use it all the time.


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