Function buildLathe

Surface-of-revolution geometry: revolve a 2D profile around the Y axis to produce columns, balusters, vases, dome roofs, light fixtures, doughnut shapes.

The profile lies in the (r, y) half-plane — r is radial distance from the Y axis, y is height. Each profile point sweeps a ring of segments vertices around the axis. Smooth normals follow the profile's local outward perpendicular.

Conventions

• profile is a flat array [r0, y0, r1, y1, ...]. List points in order of increasing arc length along the profile. Outward surface normals assume the profile traces CCW in (r, y) space — for the typical "outer skin from bottom to top" path that means r >= 0 and y increasing.
• Profile vertices on the axis (r = 0) are allowed and produce a cone tip; the ring at that vertex collapses to a single point but each duplicated vertex still carries the smooth-shaded normal so triangles around the tip render correctly.
• segments (default 32) is the radial subdivision count around the Y axis.
• closedProfile (default false) closes the profile loop so the ring at the last vertex connects back to the ring at the first, producing torus-shape geometry from a closed 2D profile (e.g. a circle offset from the axis).

Usage

// Wine-bottle silhouette revolved around Y.
const result = buildLathe({
  profile: [
    0.00, 0.0,    // base centre (on axis)
    0.30, 0.0,    // base rim
    0.30, 0.5,    // body bottom
    0.32, 1.5,    // shoulder
    0.10, 2.0,    // neck
    0.12, 2.4     // top rim
  ],
  segments: 48
});

if (result.ok) {
  const geometry = result.value;
  // Pass to sceneModel.createGeometry(...)
} else {
  console.error("Error creating lathe geometry:", result.error);
}
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