vray freezing at transforiming vertices...

[Krzysztof Cebula]

stumbled upon new bug today beta makes vray freeze at transforimng vertices.. will try to isolate the case later and upload scene

[iToo]

Ok, thanks. We have not detected problems with VRay here, so i will wait that you upload the scene.

[Krzysztof Cebula]

ok, take a look at that one.
appears that over certain density it just wont finish up generation, at least not in any reasonable amount of time
http://dl.dropbox.com/u/108014/transforing%20verts%20freeze.zip
(p.s. thanks for inverted falloff fix! )

[iToo]

Well, basically the distribution of grass on this scene is too huge to be handled by Forest. With the current parameters, i estimate it would generare more than 80 millions of proxies. The limit for Forest/VRay would be about 3 to 5 mill. of items.

I suggest you use clumps of grass instead individual blades, disable collision detection (it has a great performance hit), and when possible limit the grass to closeup views. For distant aereal views possibly would be better to use a plain texture map, perhaps combined with some low-density Forest objects to add variety.

[Krzysztof Cebula]

ok, thanks for the pointers ill do some more research then

[Krzysztof Cebula]

actually, just disabling collisions made the scene renderable again, thanks for mentioning that will avoid using that on super high number of instances ~50m instances without a problem now also ram usage seems to go waaay down without collisions turned on aswell.

[iToo]

That's great .  Really collisions have a great impact on performance because two issues:
 
1) Camera's clipping is much less efficient. Without collisions Forest can exclude large areas from scattering (at least, everything behind the camera), but using collisions the full area must be processed, excluding the items on a second phase.
 
2) Beyond certain value, although you increase the density of the Distribution map, the number of visible items doesn't change significantly (because most of them are removed because collisions). Instead, the scattering process time grows exponentially.
 
So, for dense distributions (as grass) i suggest to use a Full Distribution map, collisions disabled and Random Translation enabled (to avoid the grid look). Then, you can adjust the density to get the desired result. The grass tutorial includes a sample scene using these parameters.