Displacement won't work on some Vray meshes

[loofer]

I have a strange problem. I have models of trees that I've converted into Vray meshes but when i put a bark material on the trunk with some displacement it does nothing.

At first I thought it was a vrmesh limitation but if I make a flat plane and convert it to a vray mesh then put th material on it there is clear displacement.

Then I assumed it was a mapping issue with the tree model so I applied the material to the original and again there is clear displacement. I've also applied the material to cubes, cylinders etc and it works on them all, just not on this vray mesh. I thought it might be a corrupt mesh so I re-made it from sctratch but again, no luck.

Heres a few images.




the effect is subtle but you can see the displacement on the edges.




I have 2 questions really.

1) Why won't the displacement work on the vrmesh tree when it works on a vrmesh plane

2) Why, when the effect is so subtle on the planes (1m x 1m) is it so damned big on the trees which are full size and have been xform re-set?

[vlado]

1) Why won't the displacement work on the vrmesh tree when it works on a vrmesh plane

V-Ray proxies are in a ready-to-render format; that means that they can't modified once they are exported (this is part of the reason for their efficiency). For this reason, they can't be displaced either. However, you can apply the displacement before exporting the proxy (f.e. through the 3ds Max Displace modifier).

2) Why, when the effect is so subtle on the planes (1m x 1m) is it so damned big on the trees which are full size and have been xform re-set?

When you apply displacement through a material, the actual displacement amount is determined by the size of the object (this is how 3ds Max normally works). If you want to disable this, turn off the "Relative to bbox" option in the global V-Ray displacement settings.

Best regards,
Vlado

[loofer]

Thanks for the reply Vlado, the bbox info is useful info.

Unfortunately I should have specified I wasn't using the vray displacement modifier, I was using the displace setting in the vray material slot. I've played around a bit more with this so let me explain where I am at the minute.

If I make a vray mesh and put a map in the displace slot within the material, it does nothing.

If I apply a UVW map modifier to the vray mesh then the displace value takes effect but, as you say, the UVW map modifier 'breaks' the vray mesh.

I tried putting a Vray Displacement modifier on the original object before making the vray mesh but the displacement didn't carry accross.

I just can't find any way to transfer a displacement map to a vray mesh.

I only really need the displacement for trees that are close to the camera, so if it comes to it I can just put one normal tree in there and use proxies with bump maps for the rest. I was just curious if it was a solveable problem.

[super gnu]

you can subdivide the mesh of the tree (before converting to proxy) very finely, then use a max "displace" modifier to do your displacement, but to get fine detail youl need a tree model with 10's of millions of polygons.

the reason you are having trouble is displacement is typically a rendertime effect. you cant see it in the viewport as it subdivides the mesh into squillions of polygons when rendering. this cannot be done to proxies as they are "frozen"

the only method to "bake" displacement into an object of any type in max is to use the "displace" modifier. but as i said, you need an extremely fine mesh to get good results.

to be honest youd probably be better, like you said, to have proxies with bump maps for the majority of the scene, then a non-proxy mesh tree with vray displacement in the foreground. (putting a map in the material displacement slot gives the same result
(at default settings - see "default displacement" in the vray settings) as the vray displacement modifier on 3d displacement mode.

[loofer]

Thanks gnu, the more I play with this the more I was beginning to suspect that may be the case.