Point Trail

Records the position history of each point over time and outputs trailing paths — with built-in fading, smoothing, and a points output for dotted trails.

Category: Shapes Menu path: Shapes > Point Trail

Ports

Port	Type	Direction	Description
points_in	points	input	Points to track (typically from PointAdvect or TrackPoints)
out	shape	output	One open path per tracked point. Per-vertex curveu attribute (0 = tail, 1 = head); per-vertex colors when fade > 0; per-path index + inherited color
points	points	output	Every trail sample as a point — feed DrawPoints for dotted trails. Carries curveu, opacity (the fade ramp), sourceIndex, and color (when inheriting)

Parameters

Param	Type	Default	Description
trailLength	scalar	30	Maximum number of samples kept per point
everyNth (UI: "Frame Interval")	scalar	1	Sample every N frames. Higher values cover a longer time window with fewer vertices
outputMode	enum	Polyline	Polyline = straight segments. Smooth = Catmull-Rom beziers through the samples — silky curves, especially with Frame Interval > 1
fade	scalar	0	0 = solid trail; 1 = tail fades to fully transparent. Writes per-vertex colors, so DrawShape renders a smooth gradient along each trail (note: this overrides DrawShape's stroke color — the trail tint comes from the source point color or white)
fadePower	scalar	1	Shapes the fade ramp: 1 = linear, >1 = holds opacity near the head then drops, <1 = fades immediately
inheritColor	boolean	false	Copy each source point's color attribute onto its trail (per-path color; also tints the fade gradient)

Expose Channels

When enabled (E button on node header), adds input ports that override params via edge connections:

Port	Type	Overrides
trailLength_in	scalar	trailLength

How It Works

The trail at any frame is a deterministic function of the timeline: the upstream points sampled at the current frame and the trailLength sample frames behind it. When you scrub, export, or jump anywhere, the engine re-evaluates the upstream point chain at those history frames and rebuilds the exact trail — no warm-up, no stale state, no dependence on what was played before. A snapshot cache keeps sequential playback incremental (one upstream sample per frame), so the rebuild cost only appears on cold jumps.

Practical consequences:

• Scrubbing to any frame shows the correct full trail immediately.
• Exports match the preview exactly, regardless of the export's start frame.
• The old "Building trails" pre-roll pass is gone — it's no longer needed.

Points keep their trails as long as their stable IDs persist; a point that disappears upstream takes its trail with it, and a reborn ID starts fresh.

Frame Interval × Trail Length controls the time window: (trailLength=30, frameInterval=1) covers 30 frames of motion at full density; (30, 3) covers 90 frames at ⅓ density.

Usage Examples

Basic: Particle trails

Grid → PointAdvect (Noise vectorField) → PointTrail (trailLength: 60, fade: 1) → DrawShape (strokeWidth: 1, fillEnabled: false) → Output. Each particle leaves a 2-second trail that melts away at the tail.

Comet trails from tracked footage

TrackPoints (Features) → PointTrail (Smooth, fade 1, fadePower 2) → DrawShape. Tracked features sprout smooth comet tails that follow the footage.

Dotted trails

PointTrail's points output → DrawPoints. The opacity attribute already carries the fade ramp, so dots dissolve along the tail; map curveu through AttributeToField to drive per-dot scale too.

Colored trails

PointAttributes (target: Color, ColorField from Gradient) → PointTrail (inheritColor: on) → DrawShape. Each trail takes its particle's color.

Tips

• Smooth mode pairs well with Frame Interval 2–4: fewer samples, rounder curves, longer time window.
• A cold scrub re-evaluates the upstream point chain up to trailLength times for that one frame. Pure CPU chains (Grid/PointAdvect/fields) are effectively free; if the chain samples video via ImageSample, prefer moderate trailLength values.
• fade uses per-vertex colors, which take priority over DrawShape's stroke color — turn on inheritColor (or color the points upstream) to control the tint.
• For per-vertex effects beyond fading, the curveu attribute (0 at the tail, 1 at the head) is always written — drive opacity/strokeWidth via ShapeAttributes + AttributeToField.

Related Nodes

• PointAdvect — the usual upstream: particles flowing through a field
• TrackPoints — tracked footage features as trail sources
• DrawShape — renders the trail paths
• DrawPoints — renders the points output as dots
• ShapeAttributes — custom per-vertex styling on trails