Purpose

Field Lines samples a velocity field into short line segments. Each segment points along the local vector; its length and color can show speed. Use it to inspect Force Field or a solver’s published velocity without changing the simulation.

Use

Place Field Lines in the Geometry view, under Solvers. On Resources, add a velocity Connection and choose a published velocity resource. Force Field and Gas / Smoke publish one; FLIP Liquid needs Publish Grid Fields enabled first.

Start with Density at 12 on each axis, Length at 0.05 and Reference Speed at 2. Turn Normalize Length on if fast vectors obscure neighboring samples. Use the line output in a downstream POP workflow that preserves its topology.

Inputs and outputs

The velocity input reads the producer’s vector grid and world bounds. P carries the segment endpoints and Cd carries their colors. Each sample contributes two points forming one independent line segment.

An unconnected or unavailable field cannot supply vectors. Check the Connections row Status if nothing appears.

Controls

• Density sets the number of samples on each axis, independently of the producer’s grid resolution. The default 12 by 12 by 12 produces 1728 segments.
• With Normalize Length off, Length multiplies the field vector. With it on, nonzero vectors use a fixed length in world units.
• Reference Speed is the speed that reaches Fast Colour. Slower samples blend from Slow Colour; higher speeds stay at Fast Colour.
• Minimum Speed collapses segments below the threshold to zero length. It does not reduce the allocated sample count.

Notes

These are instantaneous vector samples, not particle trails or integrated streamlines. Sampling uses the nearest grid cell, so the view preserves cell-to-cell changes.

Density is capped at 64 per axis. Raising all three axes multiplies the sample count. Field Lines has no simulation state or rebuild step.

Ports

Inputs

• velocity velocity field

Outputs

• P lines
• Cd lines

Parameters

Field Lines

Density (Densityx) Int op('field_lines').par.Densityx

Default:

12

Range:

1 to 64

Density Y (Densityy) Int op('field_lines').par.Densityy

Default:

12

Range:

1 to 64

Density Z (Densityz) Int op('field_lines').par.Densityz

Default:

12

Range:

1 to 64

Length (Length) Float op('field_lines').par.Length

World units per unit of field value, or the fixed arrow length when Normalize is on.

Default:

0.05

Range:

0 to 2

Normalize Length (Normalize) Toggle op('field_lines').par.Normalize

Default:

Off

Options:

Off, On

Reference Speed (Referencespeed) Float op('field_lines').par.Referencespeed

Speed that reaches the fast colour.

Default:

2

Range:

0.01 to 20

Minimum Speed (Minimumspeed) Float op('field_lines').par.Minimumspeed

Default:

0

Range:

0 to 1

Slow Colour (Slowcolorr) Float op('field_lines').par.Slowcolorr

Default:

0.1

Range:

0 to 1

Slow Colour G (Slowcolorg) Float op('field_lines').par.Slowcolorg

Default:

0.25

Range:

0 to 1

Slow Colour B (Slowcolorb) Float op('field_lines').par.Slowcolorb

Default:

0.6

Range:

0 to 1

Fast Colour (Fastcolorr) Float op('field_lines').par.Fastcolorr

Default:

1

Range:

0 to 1

Fast Colour G (Fastcolorg) Float op('field_lines').par.Fastcolorg

Default:

0.85

Range:

0 to 1

Fast Colour B (Fastcolorb) Float op('field_lines').par.Fastcolorb

Default:

0.2

Range:

0 to 1