Clip maps/ trees/ lightwave

[refract]

Ok,. doing trees. Lots of them. Alpha maps kill rendertime in Vray.. (and I've been through the cgtalk thread of trees and grass)
so I've heard of clip maps from Lightwave, years ago,.. also and how it subdivides geo at rendertime and clips off the geo from the alpha at
rendertime...... which brings me to this Vray example.

http://www.spot3d.com/vray/help/150S...splacement.htm

It appears that is what it is, but its not working like Lightwaves clipmaps or I'm not doing it right.

I have a scene at work with geo trees that are instances and they render fine, but someone set up some alpha trees in the background
and Vray just hangs on a few buckets forever on those trees.

So my question is,. ... does Vray have "clip maps"?.. like in Lightwave and/or is there a way I can approach it in Maya?
Or is my only option setting "Max transparency levels" to 2 or 3?

thx

john

[aweidenhammer]

In my experience in doing a lot of trees, we tried to model the basic shape of the leaf. We didn't rely on alpha clipping as that was slower. We actually had multiple resolutions of the leaf that we could switch to depending on distance. far away, they were just single polys. Mid they would be a rough approx of shape, and closeup we would have a reasonably detailed leaf. Nothing crazy. That's also the general idea of how we do it where I work now as well.

As for a clipping trick, if there is a way to accel it in vray, I'd like to know. I'm not aware of it.

Andrew

[Zach Gray]

Nothing scientific, but I read somewhere that turning filtering off for your alpha texture gives you a decent speed boost.

Edit: found it..

http://www.pixelab.be/blog/2008/03/1...n-vray-part-1/

[refract]

Yeah we ended up just modeling the leaves. I took a quick look at the iCube trees and those don't use alpha maps either,.. hence them rendering out huge instanced forests of proxy's.

[Metzger]

Yeah, I went down the transparency map road once and never again! It's better to model everything and just proxy. You also get perfect depth passes from this as well.

The more you treat V-Ray physically, the better off you will be.

[mr furious]

same conclusion here... card leafs with transparencies = pain. Go geo all the way, but faster and then you can even put some shape in your leaves and get better looking light modeling.