Hi, I am really scratching my head on this.

I am trying to build a simple grass asset, using houdini fur tools.
I used a furSop to build some curves, and a couple of cvex shaders for the skin attributes and guides attributes.
I can see the effect of the cvex code on the curves in the viewport, and in mantra.
The strands are shaded, I took care of the orient attributes by randomizing it.
Everything works correctly.
I then decide to use a fur procedural, to be able to up the number of grass blades to a bigger without making my pc burn.

I feed the necessary information to the fur procedural node.
It works fine to, I struggled a little with the orient attributes, which I set in sops ( I had to migrate it to cvex guide shader for mantra to pick it)

All is nice, but the bad part is coming …
As soon as I open the type property window to promote some parameters. The fur procedural “stopped working” ( I saw it in the progressive render view, which was active at the time )


I retried the exact same set up from scratch, saw it work again, and then stopped working …
And now I can never get it to work again.
I really don't get it.

Does someone have a clue ?
Ps: I join the asset containing the set up I am talking about
Sorry for the long explaination

I finally made it work.
I'm still not sure about what I was doing wrong. I tried to work around the problem I had before, so I don't know which one of the changes did the trick. But I suspect it was the guide geometry that was (one of) the problem(s). By that I mean I didn't specify any reference for any guide geometry on the mantra fur_procedural shader
I also suspect that it needs to have absolute paths to nodes: I used “opfullpath” expression everywhere I had a relative reference to a node in the asset.( it seems obvious now, but weirdly , there was no message to warn me about absolute references in the asset, as I have usually)

I attached an image of the current result so far.
I was a little surprised to see that this image took the same amount of RAM ( around 15 giga) , using Sop fur procedural and using Mantra fur procedural.
Besides the fact that Houdini doesn't have to generate fur curves when exporting to mantra ( if I understand it well ), is there some other advantage ? memory wise ?

Hey gui2one,

great result!

I've honestly never found any memory difference in using the mantra fur procedural… And having the curves created in SOPs allows you to do so much more with them after the fact…
for example, creating shadow volumes for fur or even what we did with our own grass system which was to procedurally polywire curves that are super close to camera in order to create detailed “close-up” grass and a scattered falloff to much lighter grass in one easy system…

So basically yeah, I've found more uses for the fur SOP than the mantra procedural… but maybe that's just me?? :-D

thanks for the feedback ^^

I think nice to have the option not to export a ton of geometry at render time ( if you have millions of grass blades ) when it can be generated directly by mantra. The main advantage is there I guess.

Actually, now I use both in my setup, because of course I wanted my grass to be dynamic. Simulating hundreds of thousands of grass blades was not an options. So I simulate only some guides (Sop version ) . and the mantra interpolates a ton of new blades in between them.

It works pretty fine, but I must say, I though it would be a lot easier to set up.
I learned a lot though