2024
 
1.0

OpenVDB Particle system Improvement

WIP
Last modified: 10 March 2025

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This page is a part of continuing efforts to make the LightWave documentation complete. If a link takes you back to the main page, it leads to a page that hasn't yet been created. Let us know if you find one!

The ability to emit particles from the vertices of polygons converted to VDB objects was added in 2019.1. These particles can either be static or move with the addition of a Solver node. Also, a Collision Velocity setting has been added to particles to simulate real-world situations better. The Solver node now has settings divided over three tabs, and new elements are detailed below:

Simulation

Solver_Sim.png

  • CFL Factor - The Courant–Friedrichs–Lewy condition is necessary for convergence when solving OpenVDB calculations. In short, it determines how far your particles can move in a single step. At its default of 100 %, movement will tend to be more sluggish than a simulation with a CFL Factor of 10 %.

Surface

Solver_Surf.png

There are four fields here, only one of which is available while the Blobby toggle is checked.

  • Blobby - Check to treat the particles as spheres

  • Halfwidth - This is the field that is available whether or not Blobby is checked. The name is a contraction of " Half Bandwidth," and the value uses the symmetricality of the VDB inner band of particles to reduce calculation time. The default value of 3 should be good for most purposes, but you may want to raise the value if you intend to pad active areas for scattering. Lowering the value will speed things up, but you risk errors and holes in the data

  • Close - Dilate the grid to close holes then erode closing openings

  • Dilate - Dilate the grid along its normals making it bigger

  • Gaussian - Gaussian smoothing

Visualize

Solver_Vis.png

Aids for visualization of a VDB object. There are five categories

  • Show Particles - Shows the particles making up the VDB

  • Show Grid Velocity - Lines showing movement, strength, and direction. RGB colors map to XYZ directions

    • Show Staggered - Staggered shows the native side-centered velocity components. Otherwise, the velocity components will be collapsed into a cell-centered display

  • Show Collider Grid - Shows the collision voxels

  • Show Grid Voxels - A visual display of the voxel cubes that make up the grid

  • Show Pressure - Pressure levels produced by the Solver simulation are shown in color with this option checked. Red for low-pressure areas moving to white the higher the pressure

    • Gradient - Shows the gradient of the pressure using a vector field indication

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Add a Saver node to save off a cache of vdb files and use an OpenVDB Info node to play back the cache without calculation.

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Contributed by Richard Feeney