BiarcFit — Gumroad Product Listing

Product Name

BiarcFit — G¹-Continuous Curve Fitting for Blender (Free)

Price

$0+ (Name Your Price / Free)

Thumbnail

Use nostromo-deep/curves/biarc.svg on #070809. "BIARCFIT" in cold gray #6B7B8B.

Short Description (Gumroad summary field, 160 chars)

Fit a G¹-continuous biarc to any curve. Replaces noisy NURBS or polyline input with provably tangent-continuous arc pairs. Foundation for InsertPrim and HolyGrail's seam handling.

Full Description

What it does

You have a curve — a hand-drawn stroke, a NURBS export, a polyline trace. You need it as a clean two-arc approximation with tangent continuity at the join. Biarc is the classical math for this.

BiarcFit:

1. Takes any input curve
2. Computes the optimal biarc fit (two circular arcs sharing a common tangent at their meeting point)
3. Outputs a clean G¹ curve, ready for sweep / extrude / seam operations

Why G¹ matters

Most curve-fitting tools give you G⁰ (positional) continuity — the curve hits the right points. G¹ adds tangent continuity — the curve doesn't kink at the join. For mesh operations (sweep, extrude, lathe), G¹ is the minimum quality bar; G⁰ produces visible creases on the swept surface.

Biarc is the simplest math that guarantees G¹. Two circular arcs meeting tangent-to-tangent. Provable. Cheap to compute. Always works.

What's under the hood

• The same biarc solver that powers InsertPrim ($19) — the difference is InsertPrim wraps it in a full seam-resolution workflow; BiarcFit is just the curve fitter
• Pure NumPy
• O(N) per fit; sub-millisecond for curves up to 1000 points

The workflow

1. Select a curve object (any type — NURBS, polyline, Grease Pencil stroke)
2. Open N-Panel → ZForge → BiarcFit
3. Click "Fit Biarc"
4. Result: a clean biarc replaces the input

Why free

BiarcFit is the foundation tool. InsertPrim, HolyGrail, and QuadDoctor all consume biarc fits internally. Making it free establishes the math substrate publicly and drives premium adoption.

Requirements

• Blender 4.0+
• Python 3.10+ (ships with Blender)
• NumPy (ships with Blender)

Changelog

v0.2.0 — 2026-05-24 (staged)

• Initial public release
• Sub-millisecond fit on typical curves
• Works on NURBS / polyline / Grease Pencil input

Tags

blender, addon, curves, biarc, G1, tangent-continuity, free, NURBS, sweep

File

biarcfit-v0.2.0.zip

Suggested cross-sell

• InsertPrim ($19) — biarc seams in a full insert-primitive workflow
• HolyGrail Auto-Retopo ($79 / $149) — uses biarc for seam handling
• ZForge Suite ($99)

Provenance

• Source: zforge_core/topology/ (biarc solver)
• InsertPrim integration: zforge_blender_addon/ operators
• Hub: Zforge/product_hub/PRODUCT_HUB.md §4 Tier 2