Spline Mask — Edit/Track/Flow-Path

Most mask nodes in ComfyUI are one-trick ponies: draw a shape, get a mask. SplineMaskMEC is the pack's unified spline node, and it packs three different jobs behind a single mode dropdown - a canvas-based spline editor, a video tracker, and a procedural "flow path" pattern generator. The pitch from the author is that one control-point canvas drives all three, so the JSON you draw in edit mode is the same shape of data the tracker and the flow generator consume.

It's a replacement too. The pack's __init__.py is explicit: SplineMaskMEC replaces three legacy nodes (SplineMaskEditorMEC, SplineMaskTrackerMEC, SplinePathFlowMaskMEC), which are gone from the registry. If you see old workflows referencing those, this is their home now.

How it works - the three modes

• edit - rasterize a single closed or open spline to a mask. The spline_type dropdown is where the flavor lives: catmull_rom (passes through points), bezier (tangent handles), polyline (straight), plus b_spline / nurbs / natural_cubic / cardinal for smooth approximating curves. Control resolution with samples_per_segment.
• track - Lucas-Kanade optical-flow tracking across a video. You pin keyframes (a list of {frame, points} in spline_data) and the node tracks the spline's control points through the footage, blending with simple lerp according to tracking_weight (1 = pure LK, 0 = pure lerp). klt_window sizes the LK window; stroke_width handles open splines.
• flow_path - forget masking; this generates an animated procedural pattern along the spline path - ribbon, wave, dust, river, smoke, sawtooth, fbm, curl noise, lightning, and more (13 patterns). frames controls the animation length, amplitude/frequency/turbulence shape the modulation, flow_direction (forward/reverse/bidirectional/oscillate) sets how it moves, and seed makes it reproducible.

There are a lot of knobs, but the tooltips tell you which mode each applies to ([edit], [track], [flow_path], [all]), and irrelevant ones are ignored - the author is careful about that.

The inputs and outputs that matter

For a first workflow you'll touch maybe five:

• mode - edit / track / flow_path.
• spline_data (STRING) - the payload from the JS canvas; keyframe list in track mode.
• spline_type, closed, samples_per_segment - curve shape and resolution.
• feather_radius - edge softness in edit/track.
• In track mode: tracking_weight and klt_window. In flow_path mode: pattern, frames, seed.

The outputs are the interesting part, because this node feeds the rest of the graph, not just a preview:

• mask (MASK) - the rasterized result.
• coords_json (STRING) - SAM-compatible point coordinates from edit mode, so your drawn spline can seed a SAM prompt instead of only a mask.
• spline_data_out (SPLINE_DATA) - structured spline data, for feeding trackers.
• info_json (STRING) - mode diagnostics.
• bbox (BBOX) - the axis-aligned bounding box of your control points, which feeds the pack's bbox pipeline.

That coords_json output is worth highlighting: draw a rough spline, then hand the points to SAM for a clean mask. Model-free authoring, model-assisted finishing.

Installing it

Standard pack install:

cd ComfyUI/custom_nodes
git clone https://github.com/Code2Collapse/ComfyUI-CustomNodePacks.git

restart ComfyUI or use Manager → "CustomNodePacks", confirm [MEC] Loading MaskEditControl node pack … in the console. CPU + small VRAM, no models required - this node is pure geometry and OpenCV, so no downloads.

Where people get burned

Expect to set tracking_weight deliberately. Pure LK (1.0) can wander on texture-less plates; pure lerp (0.0) ignores the footage entirely; the sweet spot is usually 0.6–0.8. And remember flow_path isn't a mask of your spline - it's an animation along it, so don't wire it where you wanted a plain filled region. Read which mode a knob belongs to before turning it; there are a lot of knobs, but each one is scoped.