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Curves and NURBS

The Designer has two kinds of curve placement: Bezier curves (the day-to-day choice) and NURBS curves (when you need analytic precision for lofts and rails). This section covers authoring both, with a follow-on page on lofting a curve into a mesh.

Bezier curves

The most common curve type. Anchors with optional tangent handles.

Tools:

  • Pen (P): drag-record a freehand curve. Smoothed in real time using the smoothing parameter in the Tool Properties dock.
  • Bezier (Shift+P): click-to-add anchors with drag handles. Same as the Illustrator pen tool.

Editing:

  • Click an anchor with the Select tool to expose its tangent handles.
  • Alt-drag a handle to break tangent continuity (make a corner).
  • Right-click an anchor for: Convert to Corner / Smooth, Delete, Add Handle, Reset Handles.

Anchors store position + tangent handles + an optional pressure sample (carried through when the curve was authored with a pen).

NURBS curves

Open Surfaces > NURBS > Create NURBS Curve (Modeling menu set). The Designer drops a basic NURBS curve placement; the NURBS page covers parameters in depth.

NURBS are the right choice when:

  • You want continuous-curvature interpolation (no segments).
  • You will loft the curve to a mesh and need predictable cross- sections.
  • You are matching a curve from a CAD program (most CAD packages export NURBS).

Closed paths

Both Bezier and NURBS curves can be open (a brushstroke) or closed (a shape). Toggle in the Properties pane: closed = true.

A closed curve renders with the placement's fill + stroke; an open curve renders the stroke only. To convert an open path's boundary into a closed region, run Path > Combine > Union on itself.

Stroke parameters

Property Effect
stroke Color (CSS hex or theme token)
stroke_width Width in pixels
stroke_cap butt / round / square
stroke_join miter / round / bevel
stroke_dash List of [on, off] pixel pairs for dashed
width_modulation pressure / none / curve sample

Width modulation by pressure produces calligraphic strokes from pen-authored curves.

Curve to mesh

Once a curve is authored, two paths produce a mesh:

  • Stroke as outline mesh: Path > Convert > Stroke to Mesh produces a flat extruded ribbon following the curve.
  • Loft: select two or more curves; Surfaces > Loft to Mesh builds a surface between them. See Loft to Mesh.

When to skip curves

For straight rectangles, rounded rectangles, ellipses, circles, and regular polygons, use the matching toolbox primitive (M / F / Shift+M). Those primitives carry the shape's parameters (rectangle: width / height / radius) instead of a vertex list, so they re-author cleanly.

See also