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 This page provides general information about the Displacement sub-section of the Rendering roll-out of the V-Ray Volumetric Grid.


Displacement is a technique intended to add detail to the simulation during the rendering. The idea of the Volume Grid displacement is similar to the usual geometry displacement: a texture is sampled, and the corresponding point of the fluid volume or surface is shifted in a direction at a distance determined by the texture. You can plug any V-Ray, Maya or Phoenix FD texture maps.
You can use the Mesh Preview option to check how the attached displacement map is affecting the surface when Render Mode is set to MeshOcean Mesh or Cap Mesh.




Displacement Amount | rendDisplrendDisplEnbl – Specifies a displacement strength multiplier.

Texture | rendDisplFine – Specifies the displacement map. Depending on the Type option selected, a monochrome map or a color map could be required. If a colored map is specified when a monochrome map is needed, the strength of the displacement is determined by the total intensity of the color. If a monochrome map is specified when a vector map is needed, the entire displacement points in a single direction. See the Advection Displacement with a Monochrome Map example below.

Type | rendDispltSurf – Specifies the displacement technique.

Gradient driven – Requires a monochrome texture map. The displacement amount is the texture's brightness at each point. Each point of the fluid is shifted along the gradient of the Surface channel. This means that each point in space could have a different displacement direction. This method is suitable for smoke and fire.
Surface driven – Requires a monochrome texture map. The displacement amount is the texture's brightness at each point. Each point of the fluid is shifted along the normal of the point's projection on the isosurface of the fluid's Surface channel. The texture is also sampled at the projection point.  Unlike the Gradient driven displacement, this ensures that all points above of below the fluid surface will be displaced in the same direction, and so displacing fire/smoke simulations produces better results that are more similar to displaced solid geometry surfaces. However, the Surface driven method is slower than Gradient driven.
Vector – Requires a colored vector texture map (with negative and positive values). The point is shifted by the texture color interpreted as a 3D vector. This displacement mode is intended to be used with the Ocean Texture | PhoenixFDOceanTexture texture but can be used with any other vector displacement texture.

    • If Mode is set to MeshOcean Mesh or Cap Mesh, then it requires a texture in the format used for V-Ray Tangent Vector displacement, where X and Y of the texture are 0.5-based, and the Z direction is 0.0-based. This means that if you use a texture where the Red and Blue colors are gray and the Green color is black, it will produce no displacement; brighter color than these will move the fluid points along the positive axes, and darker and negative colors will displace the fluid point along the negative axes. A texture in such a format is the Phoenix Ocean Texture in Vector Mode.
    • If Mode is other than the mesh modes, Vector displacement requires a texture which is 0.0-based, so black color means no displacement, brighter colors shift the fluid points towards the positive axes and negative colors - along the negative axes. Such a texture is the Phoenix Grid Texture with its Channel set to Velocity.

Advection – Requires a colored vector texture map (with negative and positive values). A very similar method to Vector, but does not produce grainy structures for fire and smoke. Can be combined with the Grid Texture | PhoenixFDTexture, with the Grid Texture's Channel set to Velocity, to produce render-time advection. For more information, see the Advection Displacement example below.

The Type parameter is ignored when Mode is set to MeshOcean Mesh or Cap Mesh. In these modes V-Ray automatically recognizes whether the texture map is monochrome or colored and uses respectively Surface-driven or Vector displacement.

The difference between Surface driven and Vector displacement is that vector displacement can produce more complicated surfaces. For example, a wave texture in Vector mode produces waves that have a convex back side and a concave front side, in contrast with the symmetrical forms produced by Surface driven displacement.



Example: Advection Displacement


Regular smoke and fire, 5M cells


Advection displacement with the simulation's own velocity,
using a PhoenixFDTexture and multiplied by a noise map.





Example: Advection Displacement with a Monochrome Map

This example illustrates how displacement is affected when a monochrome map is passed when a vector map is needed.



Advection Displacement with a vector map between -1 and 1


Advection Displacement with a monochrome map between 0 and 1
Note that the displacement effect points in a single direction.