This page provides general information about the Displacement sub-section of the Rendering rollout of Phoenix FD.
Overview
Displacement is a technique intended to add detail to the simulation during the rendering. The idea of the displacement is similar to the usual geometry displacement: a texture is sampled, and the corresponding point on the mesh is shifted in a direction at a distance determined by the texture. You can plug both V-Ray and regular Maya texture maps, as well as the PhoenixFD Ocean Texture.
You can use the Phoenix FD Simulator's Mesh Preview option to check how the attached displacement map is affecting the surface when rendering a Liquid simulation.
UI Path: ||Select PhoenixFDSim|| > Attribute Editor > Rendering rollout > Displacement rollout
Parameters
Displacement Amount | rendDispl, rendDisplEnbl – 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 will point in a single direction. See the Advection Displacement with a Monochrome Map example below.
The Type parameter is ignored when the Render Mode is set to Mesh, Ocean Mesh or Cap Mesh. Either Surface-driven or Vector displacement is applied depending on whether the texture map is monochrome or colored.
The difference between Surface driven and Vector displacement is that vector displacement can produce more complicated surfaces, such as overhangs. 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.
Type | rendDispltSurf – Specifies the displacement technique.
Gradient driven – Requires a monochrome (black and white) texture map. The point is shifted toward the field's gradient by the texture brightness. This method is suitable for smoke and fire. The Gradient of a channel is the direction in which the value increases. In the case of a plume of smoke, the center is the densest area, and a Gradient-driven Noise displacement map will appear as bumps all over the smoke surface.
Surface driven – Requires a monochrome (black and white) texture map. The point is shifted by the texture brightness toward the normal of the point's projection on the isosurface. The texture is also sampled at the projection point. The Surface driven method is slower than Gradient driven but produces better results that are more similar to displaced geometry.
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.
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.
Vertical Fade Level | rendDisplFade, rendDisplVertFade – Specifies a vertical zone above the Ocean Level, where the displacement will be strongest. Above this zone there will be no displacement at all, and inside this zone the displacement will gradually be reduced moving up from the ocean surface. This is needed so that the ocean displacement would be applied only near the ocean surface and not to any simulated fluid splashing high above the ocean surface. This parameter is a percentage of the grid height, just as the Ocean Level option.
Fade Above Velocity | rendDisplVelFade, rendDisplVelFadeEnbl – If the fluid velocity (in voxels/sec) in a voxel is higher than this value, there will be no displacement at all. When the velocity is lower than this value, the higher the velocity, the weaker the displacement will be. This allows you to suppress displacement for the fast moving parts of the fluid where the displacement would visibly disturb the motion in an unnatural manner, and thus you can have only the still ocean surface displaced with waves. This option requires the Grid Velocity channel to be exported to the simulation cache files from the Output rollout.
The Fade Volume feature can be used when the liquid is in contact with a geometry surface such as a shore or a ship and the displacement breaks the contact by moving the liquid mesh away from, or into the geometry.
Use Fade Volume | usefadeobj – When enabled, allows you to specify a geometry object as a fade volume. There will be no displacement inside this object and outside it the displacement will be gradually reduced at a distance specified by the Volume Fadeout Distance parameter.
Set Selected Object as Fade Volume - When a polygon mesh and a PhoenixFDSimulator are selected, the selected object will be used as the displacement Fade Volume of the simulator.
Fade Volume | usefadeobj, fadeobj – Specifies a geometry that is going to be used to zero out the displacement inside its volume. There will be no displacement inside this object and outside it the displacement will be gradually reduced at a distance specified by the Volume Fadeout Distance parameter.
Volume Fadeout Distance | displgeomfade – Specifies the distance in world units around the object where the displacement will fade out.
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.