Negative Displacement

[jreynolds]

How does VRay handle negative values in floating point displacement maps?

They are clipping the render time geo with my current setup which is to use the displacement channel of a VRayMtl and let the render setting override Max's defaults with a few simple adjustments. I am using an EXR with actual negative values, not offset in Max.

Is there an ideal way to take advantage of negative displacement? We usually export this type of map directly from Mudbox but for this project I'm offsetting it in Fusion so that it is centered around zero. I've found in other projects that this really helps in understanding the proxy model as the medium depth for animators as well as giving a more accurate representation of what is intended and not creating a bloated look.

Best regards,
--Jon

[Morbid Angel]

Im not sure I quite understand, but I would recomend to take the positive map and just click invert in 3ds max texture map options.

[vlado]

In 3ds Max, V-Ray will clip any displacement map between black and white, so you need to modify its Output settings to bring it into this range. Then you can use the Shift parameter in VRayDisplacementMod to bring it back down.

So if your displacement map is between -1 and 1, you'd set the output RGB level to 0.5 and the RGB offset to 0.5 for the map. This will bring it into the black/white range. Then in VRayDisplacementMod, if the Amount is X units, set the shift value to -X/2.

All this is necessary because V-Ray must have some idea about the displacement bounds. We can do this automatically in e.g. Maya, because all textures are V-Ray texures, but there is no way to do this automatically in 3ds Max.

Best regards,
Vlado

[jreynolds]

Cool thanks for the great explanation Vlado

Ever since you created the "Override Max's" I've found that it's quite quick to work with for most situations. Is there any chance you might add a bit more control similar to what we can access with the modifier?

--Jon

[vlado]

The problem with that is that the global options are... global They will apply the settngs to everything in the scene. The modifier is local only for the objects it is applied on.

I guess it would be more appropriate to have a material or texture that allows the extra control.

Best regards,
Vlado

[jreynolds]

For some reason it seems to make sense that the RGB Offset of an output alone could be considered analogous to the shift of the VRayDisplacement Mod. So I'm thinking that I should be able to give a standard 0.0-1.0 map an offset of -0.5 to push it into negative displacement and center it around 0.0.

Changing the displacement multiplier from say 1 to 10 would push this type of map from -1, 1 to -10, 10

Best regards,
--Jon