Add Fill Point

Introduction

M-Star CFD uses a 3D flood fill algorithm to generate region tags over the lattice at runtime. Each fill point defines the origin of a volumetric expansion that marks all reachable voxels until blocked by static geometry or the simulation bounding box. The resulting tagged regions are central to several workflows, including defining the active region stored in memory, initializing disconnected regions with different fluids, scoping global variable reductions, and defining particle or scalar injection locations.

Fill Point Tutorial Video

After defining the static bodies (whether single part or multiple components), fill points are placed to seed the flood fills. At time zero, the solver expands from each fill point until reaching static boundaries or the bounding box, tagging connected regions and distinguishing them from disconnected ones. This approach automatically decomposes the system geometry into distinct regions, without manual preprocessing. Conceptually, the 3D flood fill behaves like an expanding balloon: it grows outward from the fill point, conforming to the geometry and stopping at boundaries. Because this decomposition happens algorithmically at runtime, there is no need to import separate geometries, construct region masks, or duplicate models.

Fill Points on the Main Lattice

The Fill Point on the main lattice is required for every simulation. When a fill point is added under the Main Lattice, the resulting tagged region defines the active portion of the domain — the set of lattice voxels that are allocated in memory and included in physics calculations. The 3D flood fill is performed once at time zero. Voxels inside the tagged region are active; voxels outside are excluded entirely and have no impact on the simulation. This distinction between active and inactive zones is fundamental for both solver performance and physical correctness. Because the flood fill point under the Main Lattice determines what is stored and solved, it is critical to verify that the tagged region correctly represents the intended interior volumes of the system.

Access

When you select Add Fill Point on the applicable context-specific toolbar, a new fill point is formed and the property grid below will launch.

Property Grid

General

Point

m | This is where the location for the fill point is indicated. The location can be moved or modified by adjusting the coordinates. The point can also be moved or rotated by using Move and Recenter on the Fill Point Toolbar.

Location

The Add Fill Point form is found on the following context-specific toolbars:

Main Lattice

Fill Point Output Data

Fill points do not introduce any new files or output streams. They are used internally to generate region tags across the lattice.

Fill Point Toolbar

Context-Specific Toolbar Options	Description
Move	The Move form enables three-dimensional rigid body transform of object through free drag or point-to-point snapping.
Recenter	The Recenter command snaps a plane to the center of the bounding box.
Help	The Help command launches the M-Star reference documentation in your web browser.

See also Child Geometry Context Specific Toolbar.

For a full description of each selection on the Context-Specific Toolbar, see Toolbar Selections.