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Rendering hair


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I thought this may be the place for it.

I have a nurbs curve copied to a model head. After this i have a vex shader attached. I then merge the model with the copied geometry and have the render flag on the mergeSOP. The model has its own shader.

My problem is the hair wont render! - only the head does. When i simply try a vew render, mantra will die on me when it gets to the hair!?

Any suggestions??


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Did you set the 'width' attribute for the curves? Also, you might want to use a Shader SOP to assign shaders separately to the head & the curves.

Over at the VEX section, there's a thread for hair. In the thread, Marc mentioned a 'magic width' Vex SOP by Peter Bowmar. You might want to check it out.

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Hey Steven

Yep, i had a seperate shader for the copied curve and the head. I also did add an attribcreateSOP to vary the width for the curve.

I'll hunt down Peter's "magic width" vexSOP and see if this makes a difference.


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have you tried rendering just the hair, and did that work?...

if it did, check to see if the width attrib is still there after the merge...

- Good luck...

(PS: it usually works....wait and see...you'll like it when it does...)

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I looked at your hip file & found out what went wrong. You used mantra3 instead of mantra, that's why View:Mantra worked while rendering with mantra1 didn't.

I got puzzled as well why the hair doesn't show up so thought something might be wrong in the ROP, settings wise. Then I noticed mantra3 in the command parameter.

There ya go! :)

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Ohhh yes, absolutely!

No wonder mantra is frustrating you. mantra3 is old and as of 5.5, hidden from view! :)

use a mantra5 rop and everything will be good - of course you'll have to swap to using shops instead of materials, but it's so worth it..

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ha, i knew it would be something dead simple.......it always is!!

thanks Steven!!

I am not at my machine now, ( software problems - will not see houdini for another three days!...), but i thought mantra is for SHOPS and omantra is for materials. i had used SHOPS and simply thought mantra was the SHOP renderer...? bit confused but when i have it in front of me i'm sure it will be self-explanatory.

by the way what is the difference with mantra3 and mantra5? ( maybe i should take this elsewhere? )

and yes it is v5.0.96 that i am using..

thanks again


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You're always welcome. :)

For the difference between mantra3 & mantra, there's already a thread here.

You can use mantra for everything, SHOPs & MOPs. The conversion is transparent to the user so no worries there.

The only problem is you can't assign MOPs using the Material SOP as mantra can't convert MOPs from the SOP level.

You can however work around it using the following method:

a. Create a Generic Surface SHOP

b. In the mantra parameter, type the following:

`execute("matvex -c material-name; matvexparm material-name")`

matvex is to convert MOPs to .vex & matvexparm is used to extract all the parameters from MOPs to be assigned to the shader. You can type 'help matvex' & 'help matvexparm' in the textport for more information.

Example, using the workaround:

Create a MOP, phong1. Now, to convert it, create a Generic Surface SHOP & type the following in the mantra parameter:

`execute("matvex -c phong1; matvexparm phong1")`

Please include the backticks ( ` ) when typing. It's the key above the Tab Key.

Now, the user can use a Shader SOP to assign it at the SOP level.

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That's a great explanation Steven, cheers to you.. but don't bother getting your head in a twist (sop) about it. Rather be patient and wait the couple of weeks for 5.5 and everything will be a little easier/clearer/faster/better/prettier. :)


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I agree with you Jason though there's still a learning curve for newbies. IMHO, I feel MOPs is a necessity & I still use them in 5.5.

VOPs absolutely rocks! :D :D :D No arguments about it but needs a bit of use to be familiar with it.

Then again, I don't have the Apprentice CD to see the new videos etc. :(

Maybe my concerned are unfounded.

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