Offset Line Shapely

Functionality

Offset line using shapely library (GEOS-based). Unlike the native Offset Line 2D Lite node, this node performs a “true” offset with self-intersection removal via buffer, producing clean results on complex topology: collapsing appendices, splitting into components, holes, self-intersecting input.

Requires shapely installed in Blender’s Python:

Use developer mode of sverchok and in properties install shapely in bottom

If shapely is not installed, the node is not active

Inputs

This node has the following inputs:

• Verts - Vertices of objects. Expects an ordered vertices list. Only X and Y are used; Z is ignored (2D offset). Accepts a list of contours (one path per element).

• Offset - Offset distance. For Polygon end type: positive grows the area, negative shrinks it. For ClosedLine and Open* types the sign flips the side of the “capsule”.

• Miter_limit - Ratio miter_length / |offset|. Used only when Join Type = Miter. If the real miter spike is longer than miter_limit * |offset|, the corner is clipped (effectively to a bevel). Default 2.0 (same as Clipper). Clamped to 1.0 minimum.

• Quad_segs - Segments per quarter circle (90°), controls arc smoothness. If > 0 — used directly, Arc_tol is ignored. If <= 0 — computed from Arc_tol. Default 8 (shapely default, coarse); 16–32 gives smooth arcs; > 64 is visually indistinguishable from a perfect arc.

• Arc_tol - Absolute arc tolerance (in scene units). Used only when Quad_segs <= 0. Converted to quad_segs via the sagitta formula: theta = 2 * acos(1 - arc_tol / |offset|), quad_segs = ceil(pi / theta), clamped to [1, 512].

All parameters except Verts are optional: if a socket is not connected, the value comes from the node’s property. If connected, a list is supported (one value per contour; if shorter, [0] is reused).

Options

Join Type - controls how corners between segments are handled:

• Miter - Sharp corners; the miter spike is limited by Miter_limit. Shapely join_style = 2 (mitre).

• Round - Rounded corners; arcs are tessellated with Quad_segs segments per quadrant. Shapely join_style = 1 (round).

• Bevel - Flat cut of the corner. Shapely join_style = 3 (bevel).

  Note

  Bevel is not an equivalent of Clipper’s JT_SQUARE. Clipper’s JT_SQUARE produces a 45° cut (“square” corner); Shapely’s bevel produces a flat cut. There is no direct analogue of JT_SQUARE in Shapely — Bevel is the closest visually.

End Type - controls the topology of the offset result:

• Polygon - Offset of an area. Polygon.buffer(d): d > 0 grows outward, d < 0 shrinks inward. Output: all rings (exterior + holes), each closed.

• ClosedLine - “Capsule” around a closed line: LineString(ring).buffer(d, cap_style=round). Output: all rings of the capsule polygon, closed.

• OpenButt - “Thick” line with flat caps: LineString(pts).buffer(d, cap_style=flat). Output: a closed capsule (exterior ring + possible holes).

• OpenSquare - Same, square caps (protruding by d): cap_style=square.

• OpenRound - Same, round caps: cap_style=round.

  Warning

  Open* types produce a closed capsule, not a single one-sided offset line. LineString.buffer returns a polygon (“thick” line); its boundary is two offset lines (left and right of the original) plus caps. This is not the same as Clipper’s ET_OPENBUTT, which returns one line (offset in one direction). Use Offset Line 2D Lite for a one-sided offset, or add a half-edge filter (heuristic by normal, not always reliable).

Outputs

This node has the following outputs:

• Vers - Result vertices. Each vertex is [x, y, 0.0] (Z is always 0). The output is a list of lists: multiple rings/contours may be returned if shapely produced a multipolygon, a polygon with holes, or several components.

• Edgs - Result edges. For closed outputs — a cycle [i, (i+1) % n]; for open outputs — a chain [i, i+1]. Also a list of lists, matching the structure of Vers.

Behaviour Notes

• Polygon with negative offset may produce a MultiPolygon if the shape splits into parts. The node handles all polygons: every ring (exterior + holes) of every polygon becomes a separate contour in the output. This is correct for a “clean” offset.

• Polygon with negative offset may produce a polygon with holes if an inner “island” does not collapse. The hole is emitted as a separate closed ring (its winding may be opposite — take this into account in downstream processing).

• Invalid input polygon: if Polygon(ring) is not valid (self-intersecting, degenerate), the node calls buffer(0) to repair it before applying the offset.

• quad_segs takes priority over arc_tol. To control smoothness only via arc_tol, set Quad_segs = 0.

• The node does not crash when shapely is missing: it draws an ERROR indicator and returns empty outputs.

Examples of usage