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Displacement is a technique intended to add detail to the simulation during the rendering. The idea of the Phoenix 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 texture maps.
You can use the Phoenix FD Simulator's Mesh Preview option to check how the attached displacement map is affecting the surface when surface when Render Mode is set to Mesh, Ocean Mesh or Cap Mesh.
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The Type parameter is ignored when Mode is set to Mesh, Ocean Mesh or Cap Mesh. In these modes Phoenix automatically recognizes whether the texture map is monochrome or colored and used 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. |
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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 Phoenix FD Ocean Texture but can be used with any other vector displacement texture.
- If Mode is set to Mesh, Ocean 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 0.0-based vector texture map (with negative and positive values). A very similar method to Vector, but does not produce grainy structures for fire and smoke. It requires Can be combined with the Phoenix Grid Texture, with its Channel set to Velocity, to produce render-time gridless advection. For more information, see the Advection Displacement example below.
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